31.12.18

Kysymyksiä ja vastauksia Värjärin tietopiiristä.

Kutoma- ja paperiteollisuus 11, 1914

(Jatk. n:o 9:een).

Kysymys.
Onko potaskakin, koska sitä käyttäen voidaan valmistaa saippuaa, live?
Vastaus.
Suoranainen live eli hydroksidi ei potaska ole, vaan kyllä lipeinen aine. Kokoumukseltaan on potaska suola. Se on hiilihapon ja kalilipeän yhdistys. Kemiallinen kaavansa on K2CO3. Se syntyy siten, että hiilihappo saa vaikuttaa kalilipeään. Näiden aineiden yhtyminen käy seuraavan kaavan mukaan:
KOH + H > CO3 = 2H2O + K2CO3 
KOH + H > 

Kysymys.
Onko edellä esitetty kaava yleistä laatua, koska sen esille toitte. Sehän näyttää varsin vaikealta?
Vastaus.
On. Upeiden ja happojen keskinäinen yhtyminen käy aina niin, että lipeän OH-ryhmä ja hapon vety yhtyvät vedeksi ja kunkin aineen jäännökset yhtyvät toisiinsa. Näin tapahtuu aina, kun live ja happo tulevat toistensa yhteyteen. Tulosta kutsutaan suolaksi.

Kysymys.
Mutta miten voi potaska olla lipeinen aine kuin se kerran on suola ja mikäli kokemuksesta tiedän, tekevät lipeät ja hapot toistensa ominaisuudet tehottomiksi.
Vastaus.
Kysymyksenne on aivan paikallaan. Ymmärrettävästi voidaan se selittää siten, että potaskassa on lipeinen osa voimakkaampi kuin happoosa ja siitä potaskan lipeinen vaikutus. Mutta suolamainen olomuotonsa tekee sen, että sitä voidaan käyttää esim. villan pesuun, johon kalilipeä ei sovellu.

Kysymys.
Miten tuhasta voitaisiin saada potaska talteen?
Vastaus.
Potaskan valmistus tuhasta tapahtuu hyvin yksinkertaisesti siten, että tuhkaa uutetaan veteen, uutos siivilöidään ja saatu vesiliuos haihdutetaan kuiviin. Puhdasta potaskaa ei se ole, sillä puutuhassa on muitakin suoloja kuin potaskaa, mutta suurin osa on sitä. Paraiden soveltuu tähän tarkoitukseen lehtipuiden tuhka.

Kysymys.
Olen kuullut mainittavan, että villassakin löytyy potaskaa?
Vastaus.
Tieto ei ole aivan oikea. Villassa ei ole potaskaa, mutta villahiessä löytyy kaliyhdistyksiä, jotka poltettaessa muuttuvat potaskaksi. Villan pesovesijätteistä valmistetaankin potaskaa suuret määrät. Samaan tarkoitukseen käytetään sokerijuurikasjätteitä, joista sokeri on oteltu pois. Suurin määrä potaskaa valmistetaan kuitenkin eräästä Saksassa löytyvästä kalisuolasta kemiallisin keinoin.

Kysymys.
Olen tehnyt havainnon, että potaska ja sooda ovat varsin läheisiä sukulaisaineita toisillleen, onko niin laita?
Vastaus.
Huomionne on varsin oikea. Aineita voi miltei kutsua sisaruksiksi. Sooda syntyy hiilihaposta ja natronlipeästä samalla tapaa kuin potaska hiilihaposta ja kalilipeästä. Sooda on myöskin lipeinen aine.

Kysymys.
Mistähän raaka-aineesta soodaa valmistetaan ?
Vastaus.
Soodaa tehdään ruokasuolasta, joka on natriumin ja klorin yhdistys eli Na Cl. Sopivin keinoin poistetaan klori ja sen sijalle pannaan CO3, joten soodan kaavaksi tulee Na2 CO3. Sooda on paljon halvempi aine kuin potaska ja yleisemmin sentähden käytännössä.

Kysymys.
Mitä sitten on ammoniakkisooda? Kysyn tällä nimellä käypää soodaa kerran soodaa ostaessani.
Vastaus.
Se on n. s. Solveyn menettelytavan mukaan valmistettua soodaa. Sitä kutsutaankin sentähden usein Solveyn soodaksi erotukseksi Leblancin soodasta. Jälkimäinen on vanhin soodan valmistustapa ja antaa soodaa, joka on epäpuhdasta. Solveyn sooda valmistetaanammoniakkisuolojen avulla ruokasuolasta ja sentähden sen nimeksi myöskin on tullut ammoniakkisooda. Se on puhtaampaa.

Kysymys.
Mitä sitten on kalsinoitu sooda?
Vastaus.
Vedetöntä soodaa, erotukseksi kidesoodasta, joissa voi olla vettä aina 63 % soodan painosta.

Kysymys.
Kalsinoitu on siis jauhoista ja kidesooda rakeista, mielestäni on jälkimäinen puhtaampaa?
Vastaus.
Aivan niin. Jauhoinen aine on aina väärennöksille alttiimpaa kuin kiteinen.

Kysymys.
Entäs kristallikarbonati. Eikö sekin ole soodaa?
Vastaus.
On. Se on kiteistä soodaa, jossa on vaan noin 18% vettä soodan painosta.

Kysymys.
Soodaa on näin ollen kaupallisena: jauheisena eli kalsinoituna ja kiteisenä, jossa on vettä 63% ja 18%, siis kolmessa eri muodossa. Oliko johtopäätökseni liian aikainen?
Vastaus.
Oli. Eräs soodan muoto on nimeltään hapansooda eli natriumibikarbonati. Huomatkaa tuo pieni lisäke bi sen nimessä. Muiden soodalajien niini on näet vaan natriumikarbonati. Hiilihapon suoloja kutsutaan yhteisellä nimellään, kuten ehkä muistatte karbonateiksi.

Kysymys.
Mistä eroaa tämä käytännössä muista soodalajeista ?
Vastaus.
Se luovuttaa hiilihappoa jos sen liuosta kuumentaa, siitä lähtee siis happoa, siitä sen nimi. Sen kemiallinen kaava on Na H CO2.

Kysymys.
Mikä olisi kaikkien näiden yhteinen tunnusmerkki ?
Vastaus.
Kaikille hiilihapon yhdistyksille on omituista se, että jos ne joutuvat tekemisiin happojen kanssa, niistä lähtee sähisten ja kuohuen hiilihappo pois. Tällä keinoin voi niistä helposti saada selvän.

Kysymys.
Löytyisikö muita lipeisiä aineita?
Vastaus.
Eräs tärkeä lipeinen aina on jäänyt mainitsematta. Se on kalkki. Sen tieteellinen nimi on kalsiumihydroksidi. Kaavansa on Ca < OH OH Siinä on siis kaksi hydroksidiryhmää. Käytännössä se käy nimellä sammutettu kalkki. Kysymys.
Voisiko sitäkin käyttää pesoon ?
Vastaus.
Voipi kyllä. Mutta saippuaa se ei siedä. Se saostaa saippuan tahraisena sakkana. Puuvillatehtaissa keitetään hyvin usein lankoja ja kankaita kalkkivedessä. Nahkuri käyttää sitä lipeisenä aineena irrottaessaan karvat vuotiasta.

Kysymys.
Kalkki poltetaan kalkkikivestä. Mitä yhteyttä on näillä aineilla toisiinsa?
Vastaus.
Sama kuin natronlipeällä on soodaan ja kalilipeällä potaskaan. Kalkkikivi on kalsiumikarbonatia eli kalkkilipeän ja hiilihapon yhdistys.

Kysymys.
Kalkkiahan käytetään rakennusteollisuudessa, mihin sen käyttö siellä perustuu?
Vastaus.
Muurilaasti, johon kalkkia paunaan kovettuu jälleen ilmasta ottamansa hiilihapon vaikutuksesta kalkkikiveksi.

Kysymys.
Laasti tiilikivien välissä ja rappauksessa ei siis enään sisällä kalkkia?
Vastaus.
Ei. Se muuttuu vähitellen kalkkikiveksi eli siksi aineeksi, josta kalkki valmistetaan.


(Jatk.)

30.12.18

Hiusten värjäyksestä.

Kähertäjä 10, 1923

Hiusten värjäys, sikäli kuin sitä parturiliikkeissä toimitetaan, lienee aina ollut ja tätä nykyäänkin on hyvin vähäistä. Siihen varmaankin vaikuttaa osaltaan sekin, että suomalaiset ylipäänsä eivät harrasta "kaunistelemista" hiustensa suhteen. Mutta syynsä on siinäkin, että kähertäjät eivät ole siihen paljoakaan huomiota kiinnittäneet. On kuitenkin täysi syy ottaa asia puheeksi, sillä tässä niinkuin kaikissa muissakin ammattitehtävissä on otettava huomioon siitä tuleva ansiomahdollisuus — joskin vähäinen sellainen. Meidän on tarkoin otettava huomioon kaikki mahdollisuudet ammatissamme, ja kun hiusten värjäyksellä on oma sijansa tehtävissämme, selostamme tässä värjäysmenetelmää.

Ensiksi hiukset pestään lämpösellä vedellä (champoneeraus). Jos hiukset ovat kovin rasvaiset, pitää rasva perusteellisesti pois pestä, kernaammin soodan eli saippuaspriin avulla, muussa tapauksessa jää väri seisahtumaan hiusten pintaan eikä imeydy hiusten sisään. Mutta suopa, sooda tai saippuasprii, sikäli jos niitä käytetään, pitää perusteellisesti huuhdella pesun jälkeen kylmällä vedellä, vastakkaisessa tapauksessa väri kehittyy liian aikaiseen eikä imeydy silloin hiuksiin vaan jää seisomaan pinnalle, jonka jälkeen se pian katoaa. Käsittely ei ole monimutkainen, vaan päinvastoin hyvin yksinkertainen. Kun siis hiukset on kuivattu (niiden ei tarvitse olla riihikuivat), alkaa varsinainen värjääminen, ja sitä varten löytyy monenlaisia värejä. Muutamissa lajeissa löytyy vaan yhtä liuosta, mutta sitä voi myöskin olla kahta, ensin käytetään n:o 1 ja kun se on kuivunut, sitten n:o 2. Useimmat hiusväriaineet värjäävät erinomaisesti, mutta vielä eivät ole kaikki aivan vaarattomia, vaikkakin tehokas tarkastus viime vuosina on parantanut asianlaitaa. Sentähden on tarkoin katsottava, että saa sellaista väriä, joka on ehdottomasti vaaratonta asiakkaalle. Jos ei tunneta värin voimakkuutta tai värivivahdusta, niin parasta on tehdä koevärjäys sen selville saamiseksi. Sen voi tehdä sellaisessa kohdassa, jossa hiukset ovat niin pitkät, että se kohta helposti voidaan peittää jälkeenpäin värjätyillä. On ylipäänsä hulluutta värjätä aivan lyhyitä hiuksia. Pehmeät hiukset ottavat helpommin väriä kuin karkeat ja tulevat niin ollen tummemmiksi samalla määrällä väriä kuin karkeat. Kun väri on kuivunut, huuhdellaan hiukset lämpöisellä vedellä ilman suopaa. Levottomaksi ei tarvitse tulla siitä, että lämmin vesi veisi värin mennessään, sillä värin pitää olla hiuksen sisässä eikä sen päällä. Se ei siis ole hiuksen pintaa, jota tehdään mustaksi tai ruskeaksi, vaikkakin moni niin luulee. Siis, kun hiukset voidaan ilman yllätystä huuhdella kaikesta väristä, jota löytyy hiusten ja ihon päällä, on värjäys sen jälkeen valmis. Seuraavana päivänä saadaan hiukset sekä pestä suopalla että kähertää, jolloin kuitenkin on käytettävä rasvaa, mutta luonnollista on, että käsittelyä ei tehdä liian kovakouraisesti.

29.12.18

White Hair and Black - "A Fact Worth Knowing."

The Scientific American 50, 31.8.1850

Uuder this head the True Union, publishes the following from "an authentic source."

"A distinguished General (Twiggs,) return. ed from the Mexican war covered with 'glory.' He had, however, two marks of hard service which laurels could not hide — as they did Caesar's baldness. One was a head as white as wool; and the other a cutaneous eruption on his forehead. For the latter he was advised to try a mixture of sulphur, and sugar of lead and rose water. In applying it, some of the mixture moistened his forehead, and after a while resumed its original color. He then applied the mixture to all his hair, and it all became, and is now, of its primitive and sandy hue. He communicated the fact to some of his friends in Washington — especially to some exmembers, who are widowers and seeking preferment — and it has been found efficacious in every instance. It does not dye the hair, but seems to operate upon the roots, and restore the original color.

"The recipe is as follows: - 1 drachm Lac Sulphur, ½ drachm Sugar of Lead: 4 ounces Rose Water; mix them: shake the phial on using the mixture, and bathe the hair twice a day for a week or longer if necessary."

[The theory of the above is neither new nor valuable: it is the sulphuret of lead applied to dye hair its own color. The nitrate of silver is much better, but those who consult their health and a steady brain, will refrain from both, and prefer the snowy locks of nature to the sable locks of art.

28.12.18

Mineral Paint Discovered in Massachusetts

The Scientific American 50, 31.8.1850

A quarry of mineral has been discovered near West Springfield, which consists of a reddish brown stone mixed with blue, which is ground, washed and dried, and then mixed with oil like lead, when it becomes an excellent fire and water-proof paint. It is considered to be a valuable discovery.

27.12.18

(Ilmoitus) Värjäys-kursseille...

Käsiteollisuus 10, 1913

Värjäys-kursseille, jotka tulevat järjestettäviksi Fredrika Wetterhoffin Työkoululla Hämeenlinnassa noin viikon aikana, alkaen tulevan tammikuun 8 p:nä etupäässä alizarin- ja indantren-väriaineitten (pellavaa ja puuvillaa varten) käytössä, kehoitetaan varsinkin semmoisia kotiteollisuuskoulujen opettajattaria, jotka ovat ennestään jonkun verran värjäystä harjoittaneet, ilmoittautumaan allekirjoittaneelle ensi marraskuun kuluessa, samalla mainiten, minkä summan matkakulut kunkin koululta Hämeenlinnaan ja takaisin tulevat tekemään. Kurssiin osanottajiksi hyväksytyille on apurahoina jaettavana yhteensä 800 markkaa 30—50 markan erinä, minkä ohella halvan asunnon ja ruu'an saannista tulee huolehdittavaksi. Helsingissä, kotiteollisuustarkastajan toimistossa 13 p. lokak. 1913.

- Lauri Mäkinen.

26.12.18

Viestejä y. m. pakinaa. Värjäyksessä...

Käsiteollisuus 10, 1913

Värjäyksessä emme suinkaan ole päässeet vielä vakiintuneelle kannalle tekstiilityönkään alalla. Vanhat kansanomaiset menettelyt ovat joko vahingossa tai epäkäytännöllisyytensä vuoksi unohdetut ja helppoudessa sekä nokkeluudessa kilvoitteleva anilinivärjäys on osoittautunut kestävyydessä varsin epävakavaksi. — Samalla kuin yhäkin koetamme kehittää vanhaa taattua kotivärjäystä, varsinkin omien kasvisaineitten käyttöä, on meidän etsittävä uudemmista värjäyskemian saavutuksista parasta, mitä kouluissamme ja kotioloissamme voimme huomioon ottaa.

Te jotka olitte tilaisuudessa tutustua viime talvena vähävenäläisiin kudoksiin Pietarin näyttelyssä, säilytätte kai mielessänne niitten kehutut värit. Vähä-Venäjällä käytetään osaksi kasvisvärjäystäkin, mutta vieläkin enemmän on joutunut siellä käytäntöön Badenista saatu alizarin- ja indantren-väriainesten käyttö. Edellistä väriainesta on meidänkin maassamme jo useita vuosia hyvällä menestyksellä käytetty, mutta indantren väri, joka on erikoisesti pellavan ja puuvillan värjäykseen sovellutettua, on meillä miltei aivan tuntematonta, eikä sitä kotiteollisuutemme hyväksi ole vielä lainkaan käytetty. Kun pellavan ja puuvillan värjäys on meillä aivan huonolla kannalla, ollaan tietenkin laajoissa piireissä halukkaat varsinkin tähän indantren-väriaineen käyttöön tutustumaan, vaikkakin se on jonkun verran monimutkaisempaa kuin se, mihin meillä viime aikoina on totuttu.

Kokeilun alkuun saamiseksi kysym. olevien alizarin- ja indantren-värien laajempaa käyttöä varten olen hankkinut tilaisuuden valtion varoilla ja Fredrika Wetterhoffin Työkoulun ja johtokunnan sekä johtajattaren suosiollisella myötävaikutuksella järjestääkseni värjäyskurssit noin 1 viikon ajaksi sanotulla koululla ensi tammikuun 8 p:stä alkaen. Kuten ilmoituksesta toisaalla lehdessämme näkyy on värjäystä ennen suorittaneilla opettajattarilla tilaisuus saada kauttani pienet apurahat sanotuille kursseille saapumista varten. Kursseille hyväksytyt saavat kutsun niin hyvissä ajoin joulukuun alussa, että voivat aikanaan määrätä kevättyökauden alkavaksi noin 16—19 p:nä tammikuuta, jolloin tämä tutustumiskurssi jo on saatu päättymään. Opetusta kursseilla tulee antamaan kysymyksessä olevan Badenin väritehtaan insinööri hra Haag Wetterhoffin työkoulun värjäyksen opettajan, värjäysteknikko Wünschen avustamana.

- Lauri Mäkinen.

25.12.18

To Remove Paint from Clothes.

The Scientific American 31, 19.4.1851

Many persons by misfortune get paint on their clothes, and from the want of proper knowledge to remove it, their clothes are spoiled for all decent purposes. This is a great loss especially when fine clothes are spotted or daubed with paint. Many fine and excellent coats have, to our knowledge, been laid aside for common purposes, because of a few spots of paint. Paint can be very easily removed from woolen clothes, although it may be quite hardened. The way to do this is to pour some alcohol on the cloth, saturating the paint, and after it has remained on it for about ten minutes, pour on a little more, and then rub the cloth with the paint spots between the fingers. This cracks up and breaks the paint from the surface, after which a piece of clean sponge dipped in the alcohol, should be rubbed on the cloth, with the grain. Paint can be taken out of silk in the same way, only it is best to steep the part of the silk with the paint on it, in a cup containing the alcohol; and it will not do to rub the silk between the fingers, for fear of breaking and creasing its surface. This is true, as it respects lute string or any hard surfaced silk, but figured soft silk, may be gently rubbed. The way to treat the painted silk, is this, after it has been steeped for about 15 minutes, then it should be spread out on a board, and rubbed along the grain with the selvage, by a sponge dipped in the alcohol. This seldom fails to remove all paint. Some use camphene for removing paint, but alcohol is more cleanly. Black paint on a white surface, or even on any delicately colored surface, always leaves a stain, although the paint, itself, strictly speaking, may be removed. It is much easier to clean a white surface, than one of a light color, like French grey, lilac, pink, &c. For cleaning light colored cloths from paint, use only a clean sponge, or if a sponge is not handy, use a piece of clean white flannel.

All the ethers are very effective, in removing paint, also grease spots, but fish oil always leaves a stain, and is exceedingly difficult to remove. There are some who use colored oils for the hair, these always make a bad stain, especially those of a red color. The reason of this is that madder is used to color them, and this is a very permanent dye drug. The best substance for removing paint, grease, &c., from all kinds of clothes, those of the darkest and lightest colors, is that beautiful ether discovered by Prof. Simpson, in Scotland, a few years ago, and by Mr. Guthrie, of America, a few years before, unknown to the Doctor, — we mean chloroform. It is employed in the same manner as the alcohol, only care must be taken to work it more rapidly, as it is more volatile, and care must also be exercised so as not to inhale it. No one should use it but careful persons of mature years it is of too high a price to be used in general, and young people, in no case, should be allowed to tamper with it.

After what has been said about the removal of paint and grease, no person need be much frightened at a paint stain on a fine cloth coat, but, at best, let us be candid and say, that upon silk it is not possible to remove the paint and leave the silk as it was before being injured. Prevention, in all cases, is better than cure, but misfortunes will take place and seldom come singly, therefore the above will be found useful and of great benefit to many.

24.12.18

Konttoritekniikan alalta. Musteen merkitys todistusvälineenä asiapapereiden väärentämisestä.

Liikeapulainen 3, 11.2.1921

Yksityinen oikeuselämämme, joka suureksi osaksi perustuu asiakirjojen käyttöön, on pakoitettu pitämään apuneuvoja, jotka jossakin määrin estävät väärennysten suorittamista. Keinot ovat kuitenkin enimmäkseen vain siinä, että väärennys voidaan todeta tapahtuneeksi ja siten moraalisesti estää uusien tapauksien lukua kasvamasta. Yleensäkin eivät mitkään asiapaperit ole ehdottomasti oikeita enää senjälkeen kun ihminen on oppinut allekirjoituksenkin väärentämään mitä loistavimmalla tavalla, joten, ja varsinkin kun mädännäisyyttä melkein joka päivä paljastuu eri aloilla, liikemiesten on täysi syy pitää silmänsä auki. —

Puhuttaessa vääristä asiakirjoista, on tehtävä ero "yleensä väärien" ja "väärennettyjen" asiapapereiden välillä. Edellinen laji esiintynee harvanlaisesti yksityisessä liike-elämässä ja tavataan se silloin useimmiten väärinä palvelustodistuksina, papinkirjoina y.m. henkilötodistuksina. Useimmat tapaukset muodostavat kuitenkin sellaiset väärennetyt asiakirjat kuin testamentit, sopimukset, velkakirjat j. n. e.

Vastauksen antaminen kysymykseen, miten itse väärentäminen suoritetaan, ei kuulu tähän ja olisikin se käytännöllisen rikosasiaintutkijan tehtävä; tärkeämpi on kysymys, miten voidaan todistaa väärennyksen tapahtuneen. Ammattimiehellä on tällä alalla käytettävänään koko joukko tärkeitä apukeinoja, kuten paperin rakenne ja laatu, vesimerkit, käsialan erikoisuudet j.n.e. sekä ne erilaiset todisteet, joita kirjoit tusmuste voi antaa.

Täten kiertyy väärennyksen selvillesaanti kysymyksen ympärille siitä, mitä mustetta esilläolevassa tapauksessa on käytetty. Todistus saadaan usein helposti käyttämällä joko kemiallista tai mikroskoopin tarjoamaa tutkimustapaa. Musteiden erilainen suhtautuminen happoihin ja lipeisiin antaa melkein pitkin matkaa erinomaisia tuloksia. Niinpä uudenaikainen rautaa sisältävä muste antaa lipeällä käsiteltynä vihreän ja sinipuumuste punaisen-punaviolettivärin sekä edellinen natriumlipeän kanssa, riippuen lisäväriaineista, joko punaisen tai ruskean ja jälkimäinen ensiksi ruskean ja kuivatettua punaisenpunaviolettivärin j.n.e. Toiselta puolen voidaan mikroskooppia käyttämällä saada näkyviin eri musteiden väliset erot.

Kuten edellä mainittiin, lisätään musteisiin erilaisia väriaineita, joiden tarkka tunteminen muodostaa väärennysten paljastukseen nähden perin tärkeän avun. Asian selventämiseksi muisteltakoon valokuvauslevyä, mikä on aivan toisin värintuntoinen kuin ihmissilmä. Jos valokuvataan tavailisella levyllä, esim. keltainen risti sinisellä pohjalla, näyttää valokuvajäljennös kuvan, jossa on sininen risti keltaisella pohjalla eli aivan päinvastoin kuin todellisuudessa. Tämä virheellisyys johtuu siitä, että levy siniseen nähden on liian herkkä, t. s. se reageeraa siniseen melkein samoin kuin valkoiseen ja esittää kummankin värin sentähden lähes samassa valoarvossa, samalla kun se keltaiseen, vihreään ja punaiseen nähden on melkein yhtä tunnoton kuin mustaan.

Tätä valokuvalaatan virhettä käytetään väärennyksiä paljastettaessa hyvin laajalti hyväksi. Esim. 100 markan velkakirja on väärennetty 1000 markaksi lisäämällä musteella yhden 0. Jos nyt 100 on kirjoitettu sinervällä musteella ja lisätty 0 punervalla, riittää valokuva todistamaan väärennyksen tapahtuneeksi: kopiossa on lisätty 0 vahva musta valkoisella pohjalla, jotavastoin 100 esiintyy vain hyvin heikkona. Silmästä näyttävät kumpikin muste aivan yhtäläisiltä.

Jotta kuitenkin samankin värin eri vivahdukset voitaisiin eroittaa, käytetään käytännössä hyväksi vielä toista valokuvalevyn ominaisuutta, esim. sitä, että se voidaan mielin määrin tehdä herkäksi eri väreille. Väärennyksiä tutkittaessa on usein musteen ikä otettava huomioon. Tämä tehtävä on mitä vaikein. Jos kuitenkin joku päivämäärä on kirjoitettu aniliinimusteella sellaiseen aikaan, jolloin sanottua mustetta ei vielä tunnettu, on väärennys sillä todistettu. Myöskin kahden eri kirjoituksen risteykset antavat tilaisuuden päättää, kumpi kirjoitus on vanhempi, sillä nuorempi muste valuu vanhemman jälkiin, mutta useimmissa muissa tapauksissa joutuu ammattimies, ellei muita johtokohtia ole olemassa, musteen kopioimiskyvyn y.m. seikkojen varaan, kuten esim. tarkkaamaan musteiden vaihteluja eri aikoina eri tiloissa j. n. e.

Uusinpana tuloksena tällä alalla on mainittava ultraviolettivärivalokuvaus, jolla, vaikkakin se vasta on alkuasteellaan, jo on saavutettu loistavia tuloksia. Hyvällä syyllä voidaan jo väittää, että luonnontieteet tarjoavat viranomaisille pätevän aseen taistelussa rikollisten väärennyksiä vastaan.

23.12.18

(1700) Dyeing Vegetable Ivory. (1707) Platina Varnish.

The Manufacturer and Builder 11, 1876

(1700) Dyeing Vegetable Ivory.
Yes; the dyes commonly used for wool will also dye real ivory. Vegetable ivory however does not take red colors quite as well as the animal article; however there is not much trouble about it. We do not know of any book specially written on dyeing ivory; but no doubt you may obtain a great deal of information from any good book on dyeing in general. We will add for your information that Black is obtained by steeping the articles in a weak solution of nitrate of silver, and then exposing it to the light; or by boiling the ivory first in a solution of logwood and then steeping it in a solution of sulphate of iron, thus making an ink. Red is obtained by an infusion of cochineal in liquid ammonia; the articles are first soaked in a water slightly acidulated with nitric or acetic acid. Blue is obtained by a solution of indigo in sulphuric acid which has been diluted and neutralized with chalk or potash. Green is obtained by a solution of verdigris in vinegar. Yellow by a bath of chromate of potash, and afterward in a boiling solution of acetate of lead. Purple by a neutral solution of chlorid of gold, and then exposure to the light.

(1707) Platina Varnish.
This varnish has been analyzed by Dr. Filsinger, of Dresden, who has published the results for the benefit of all interested. Various qualities are sold, distinguished by numbers, from No. 15 to No. 1, No. 0, and No. 00. No. 15 was found to consists of 35 per cent of linseed-oil vanish and 65 of yellow ocher; No. 11, of 37 of linseed-oil varnish and 78 of clayish iron ocher and pulverized zinc; No. 00, of 23 of linseed-oil varnish and 77 of clayish iron ocher and more pulverized size. Other ingredients besides these were not present in any of the varnishes. That a manufacturer should recommend oil paints which consist of nothing but ocher and varnish as something new very valuable, is neither original nor uncommon, but it can not be considered a very creditable act.

22.12.18

Suojelevan värin merkityksestä.

Luonnon ystävä 10, 1905

Hauskoja kokeita suojelevan värin merkityksestä on tehnyt italialainen professori di Cesnola eräillä heinäsirkkalajeilla. Hän kokeili kahdella lajilla, joista toinen on vihreä ja elelee luonnollisessa tilassa vihreillä kasveilla, toinen taas ruskea ja elää kuivilla. Joukon yksilöitä kumpaakin lajia kiinnitti hän noin 15 cm pitkillä silkkinauhoilla kasveihin, siten että sama määrä vihreitä heinäsirkkoja oli täten kytketty vihreisiin ja ruskeihin kasveihin ja samoin sama määrä ruskeita sirkkoja vihreisiin ja ruskeihin, ja että ympäristökin oli tuon kasvin mukainen. Täten kytkettyinä saivat heinäsirkat hyppiä yli kaksi viikkoa — ne nimittäin, joiden viholliset sen sallivat. Tämän ajan kuluttua olivat kaikki ne ruskeat heinäsirkat, jotka olivat eläneet ruskeassa, siis luonnollisessa ympäristössään, elossa ja samoin oli laita vihreässä ympäristössä olleiden vihreiden. Niiden ympäristön kaltainen väri oli siis tehokkaasti niitä suojellut. Sen sijaan olivat kaikki ruskeassa ympäristössä eläneet vihreät heinäsirkat hävinneet ll:n päivän kuluttua ja 45:stä ruskeasta, viheriäisessä ympäristössä eläneestä oli kokeiluajan loputtua vaan 10 elossa. Kun eläinten väri ei ollut ympäristön mukainen, olivat niiden luonnolliset viholliset, etenkin linnut, huomanneet ne ja syöneet ne suuhunsa.

— Revue scientifique.

21.12.18

Miscellaneous Summary. Best Time to Paint Houses.

The Scientific American 15, 9.4.1864

- Experiments have indicated that paint on surfaces exposed to the sun will be much more durable if applied in autumn or spring, that if put on during hot weather. In cold weather it dries slowly, forms a hard, glossy coat, tough like glass; while if applied in warm weather, the oil strikes into the wood, leaving the paint so dry that it is rapidly beaten off by rains.

20.12.18

Tulewatko miehet wärjättäwiksi?

Maakansa 184, 25.8.1922

Otsikossa ei ole mitään wikaa, waikka lukija nähtäwästikin epäilee, ettei otsikko ole niin kuin olla pitäisi. Ei ole kysymystä siitä, tulewatko miehet wärwättäwiksi, kuten lukija ehkä tahtoisi otsikon olewan, waan siitä, tulewatko miehet wärjättäwiksi.

Myöskään ei tällä kertaa ole kysymys miesten poliittisesta wäristä tai wärittömyydestä, sillä waalit omat olleet ja menneet, joten eri puolueiden agitsatsioonikansliat omwt toistaiseksi antaneet poliittisille wärjäreille kesälomaa, niin, että waalikansa saa nyt wapaasti kuljeskella minkä wärisenä tahansa. Waan on miesten wärjäyskysymys astunut päiwäjärjestykseen Parisin muotimaailman waatimuksesta.

Tosin ei Parisissakaan wielä wärjätä miehiä. Mutta se muoti saattaa tulla käytäntöön miten pian tahansa, sillä nyt jo wärjääwät parisilaiset naiset sylikoiransa leninkiensä wärisiksi.

On tunnettua, että muodin waatimuksia ei lujimmankaan miehen tahto woi seisoa wastaan. Muodit tulewat, nainen näkee, ja - mies on woitettu. Ja senpä wuoksi me juuri pelkäämmekin pahinta. Pelkäämme, etta naiswäen päähän pälkähtää jonain kauniina päiwänä ruweta wärjäämään meitä miehiä, etenkin niiden naisten, joilla ei ole sylikoiria. Eikä parempaa työtä kuin sylikoiriensa wärjääminen. Niinpä woi "Guldu" jonain aamuna esim. tuossa joulun alla wirkkaa kahwipöydässä:

"Kuules, "Pegu", sinä olet hieman liian mustawerinen, jotta woisin sinusta pitää. Sinun naamasi wäri ei sitä ka pukee sinua oikein hywin walkoisen leninkini kanssa. Olen siis aikonut walkaista sinut jouluksi, tuoppa sen wuoksi joulutarpeiden ohella kilo liitujauhoa. Tukkaasi ei kuitenkaan sowi wärjätä walkoiseksi, koska sinusta silloin tulisi harmaapää. Luulen, että punainen tukka pukee sinua oikein hywin walkoisen ihonwärin ohella. Silloin me woimme käydä myöskin wieraisilla sekä walkoisten että punaisten sukulaistemme luona, ilman, että kumpuisillakaan on syytä suuttua sinun wäriisi. Minä kyllä sitten pidän keskustelussa huolen, että niin punaiset kuin walkoisetkin tulewat tarpeen mukaan sekä kiitetyksi, että moitituksi".

Ja jos uusiin muoteihin hullaantunut "parempien piirien" nainen saa kerran päähänsä, että ukkorapukka on pantawa uuteen maaliin niin se tehdään myös, sillä muotinainen osaa taluttaa miestä mukanaan yhtä taitawasti kuin willakoiraansakin. Oikeastaan onkin miehellä ja willakoiralla "parempien naisten piirissä" wain se ero, että nainen istuttaa willakoiraa sylissään, mutta istuu itse miehen sylissä.

Mitä taas tulee nuoriin miehiin ja neitosiin, ennustamme, että jos miesten wärjääminen tulee muotiin, niin nuoret miehet eiwät jää edes odottamaan sitä, että tyttö ryhtyy heitä wärjäämään. He wärjääwät itse itsensä mielitiettynsä hameen wäreillä. Ja ne, joilla on monta mielitiettyä, maalaawat itsensä kirjawiksi kuin Zepra.

Toistaiseksi emme kuitenkaan pelkää maalaismiesten puolesta. Maalaisnaiset eiwät wielä pane niin paljon painoa wäreihin kuin wiiwoihin. Sitä paitsi eiwät talonpoikaisnaiset ole wielä oppineet edes omaa tukkaansa wärjäämään.

- Aatami.

17.12.18

Huonekalujen kultaus. (Osa 1)

Maalarilehti 2, 1927

Yleensä olemme siinä uskossa, että maalarin työvälineillä emme saa syntymään hienoa kiiltokultausta. Tämän kirjoituksen laatija, eräs saksalainen maalari, on asiasta toista mieltä, nim. että hyvinkin hienoja huonekalukultauksia voidaan maalarin keinoilla tehdä. Hänen selityksensä ja ohjeensa ovat siksi yksinkertaiset ja vakuuttavat, ettei kirjoituksen luettua voikaan jaada epäilevälle kannalle. Tässä kirjoituksessa esitämme kultauksen pohjustuksen ja seuraavassa numerossamme jatkona työn loppuosan.

Tapa kullata arvokkaammat huonekalut on hyvin vanha. Kiiltokultauksella kullattuja huonekaluja on tavattu jo egyptiläisistä kaivauksista. Kullattuja käyttöesineitä on niinikään jo vanhoina aikoina ollut kreikkalaisilla, roomalaisilla ja intialaisilla. Myöhemmillä ajoilla olivat kullatut huonekalut erittäin suosittuja 17—18 vuosisadoilla. Näiden aikojen huonekalutaide ylimalkaan oli hyvin korkealla kannalla. Niiden huonekalut ovat vielä nykyään hienompien huonekalujemme malleina. Mitä tulee huonekalujen kultaukseen, niineivät siihen sovikaan nykyaikaiset kuivaviivaiset tehdashuonekalut, vaan paremmin juuri barokin jarokokoon pehmeät ja sujuvat muodot; niissä kullan kaunis ja kimalteleva väri vasta pääsee vaikuttamaan.

Kultauksen tekotapa saattaa vaihdella, riippuen myöskin siitä, mitä kultauksesta tahdotaan maksaa. Halvin on tietysti yksinkertainen, tasainen kiilloton kultaus, öljyväripohjalle, kultaöljyllä, kultana käyttäen n. k. metallikultaa. Tämä tekotapa on kuitenkin siksi karkea, ettei se edes juuri sovi huonekaluihin, vaan käytetään sitäkauempana silmästä olevien koristeiden kultaamiseksi.

Toinen yksinkertainen, mutta hienompi kultaustapa on seuraava. Jos huonekalu on jokseenkin hyvä ja siloinen puusepän jäljeltä, tehdään tahdas kipsistä ja liimasta jolla mahdolliset lovet ja naarmut täytetään. Pinnat hiotaan sitten sileiksi. Sitten, jos puu on harvahuokoista, mahonkia tai saarnia, pinta sivellään liimavedellä tai muulla täyteaineella, esim. spriilakalla. Kuivuneena pinta hiotaan taastasaiseksi. Jokatapauksessa täytyy pinnan olla aivan sileän. Kun on siis saavuttu niin pitkälle, tehdään pohjustus. Joutuisimmin kehittyy työ jos tehdään heikon puoleinen seos shellakasta, liuottamalla sitä spriihin. Tähän pohjaan voitaisiin nyt ilman muuta sivellä "Mixtioni", kultausöljy. Mutta siten ei kultaukseen helposti tule kullan täyttä kiiltoa. Pohja on siihen liian heikko; halpaan työhön voitaisiin näinkin rajoittua.

Tukevaa ja täyteläistä kultausta varten sivellään shellakan päälle lakkaa, kerran tai kaksi, sitä ennen on shellakkapinta hiottava sileäksi hienolla hietapaperilla ja vielä kostutetulla nahkalla. Tämän jälkeen tehdään kellertävä lakkaväri, ohennettu tärpätillä, jolla pinta taas sivellään ylitse. Värin tulee kuivua puolihimmeäksi. Veistoksellisissa pinnoissa ja listoissa on huomattava, ettei väriä tule liian paksulta särmiin. Siten sivelty esine on vietävä huoneeseen jossa ei ole tomua ja jossa on n. 25 asteen lämpöinen, kuivumaan. Kuumempi lämpö saattaisi ravistuttaa esineen liimauksia ja taivuttaa sen ohuempia pintoja.

Tämä pohjaväri kuivaa n. 5—6 tunnissa. Kun se on valmis, hiotaan se taas sileäksi, hangataan kostealla nahkalla, jotta tomu siitä lähtisi tarkkaan pois. Myöskin huone, jossa esine tulee työn kuivumisaikana olemaan, on tarkkaan pyyhittävä tomusta. Nyt lakataan kullattavat paikat hyvin juoksevalla kiiltolakalla. Lakkauksen tulee tapahtua 18—20 asteen lämpimässä jotta se juoksisi parhaiten. Huomattavaa on, että hionnan tulee tapahtua enempi kylmässä ilmassa, ettei lakkapinnat hangatessa kuumenisi ja tahmistuisi. Lakkaus ei saa olla liian ohutta, mutta ei myöskään niin paksua, että se juoksisi. Huomattakoon tarkoin, että se pinta joka lakkaukselle tällöin tulee, antaa muotonsa kultaukselle; jos se siis on kylläisen ja ehyen kiiltävä, tulee kultauskin kiiltävä. Lakkaus saakoon kuivua n. 12 tuntia. Hyvä on jos voidaan odottaa enemmänkin, sillä mitä kovemmaksi pinta saa kuivua, sitä kiiltävämmäksi tulee kultaus. No niin, kun nyt niin pitkälle on tultu, sivellään lakkapintaan kultapohja, "mixtioni", lyhyellä siveltimellä, ohuesti ja hyvin tasaisesti. Mitä ohuempi on "mixtioni" sively, sitä kiiltävämmäksi tulee kultaus. Jos kullataan puhtaalla lehtikullalla, voidaan tehdä niinkin, että sivelty mixtioni pyyhki täännahkalla kevysti pois joten siitä pintaan jää vain ohutkosteus. Älköön sitä kokeiltako jos aiotaan kullata "metallikullalla ". Myöskin pantakoon metallikulta pintaan kyllin aikaiseen, ettei se ennätä kuivua niin paljoa, ettei kulta enään siihen tartu.

Jatko seuraa.

16.12.18

(2672) Lustrous Black on Wood-Work. (2674) Coloring Glass Toys.

The Manufacturer and Builder 8, 1880

(2672) Lustrous Black on Wood-Work.
- We know of nothing that will be expeditious enough to answer our correspondent's inquiry to put fine, black, lustrous finish on wood-work in the lathe; but can give him several recipes for putting on a black finish afterwards, namely: Put on two coats of black japan, the nvanirhs or polish; or use size and lampblack before laying on the japan. Or, wash the wood with a boiling decoction of logwood three or four times, allowing it to dry between each application; then wash with a solution of acetate of iron (made by dissolving iron filings in vinegar), and varnish or polish. Do not mix the logwood and iron before application. This stains so deep that ordinary scratching will not expose the original color of the wood.

(2674) Coloring Glass Toys.
- The mode of coloring these and similar toys, no doubt differs somewhat. One method, and we think the simplest, consists in preparing a solution of collodion - gun-gotton gelatinized in a mixture of alcohol and ether - adding to it an alcoholic solution of one of the aniline colors that gives the desired tint, filling the spheres with this colored solution and then emptying out the surplus. The portion remaining in the interior, by the evaporation of the solvent, speedily forms a tenacious coating of the desired color, having the high luster which is characteristic of these and similar toys. Our correspondent will find this to be a rapid and satisfactory method of accomplishing his object.

10.12.18

Photo-Trichromatic Printing. Part IV. Half-Tone and Photochromic Printing Inks.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
Although it is intended to deal principally with photochromic printing-inks, a few remarks on half-tone inks in general may be useful. Of late years so-called "art shades," i.e., reds, greens, blues, violets, and purples, subdued or saddened with a small percentage of black, have deservedly come into favour alike with the public and the printers, and particularly so since some of the illustrated papers issued supplements of reproductions of Royal Academy pictures, and other subjects, printed in these subdued colours. These art shades look very effective if used in the production of artistic commercial stationery, illustrated catalogues, menus, etc. The effect, if these broken colours are judiciously selected, is very pleasing, and many of them give half-tone printings the appearance of two shades, as if produced by two printings. Tints of various colours may with great effect be combined with these saddened hues, and I have endeavoured to give a few hints for such combinations in Part II., when speaking of the harmony and contrast of colours and the combination of triads.

For half-tone work only the very best inks should be used. The blocks on account of their flat surface take very little ink in comparison with woodcuts or type, and therefore unless the ink is made of strong pigments, or the finest carbon black, the prints will turn out flat and look washed out. Natural earth colours, such as umbers, siennas, ochres, terra-verte, etc., should be rigidly rejected, for no amount of grinding will alter their hard and gritty nature, or make them fit for the production of delicate half-tones. They also cause unnecessary wear to the fine grain of the blocks, and are only desirable for ordinary letterpress or litho-printing on account of their cheapness and the variety of browns they comprise. For halftone work all the hues of the earth colours may be produced from more suitable sources, and the printer who is desirous of turning out good work, should not mind paying a little more for better inks. Any shade of brown may be made of black and red (madder being the best on account of its great strength and permanency) with or without the addition of yellow or blue. In this way an excellent brown, imitating silver prints, may be mixed. Green-blacks, olivegreens, nut-browns, and other shades, may be produced from madder, Prussian blue, and black, without havmg recourse to earth colours, to which white should be added for diluted colours. The theory of pigmentary mixtures has been dealt with in Part II., and the chromatic clock-dial may be consulted with advantage. The mixture of such art shades should however only be undertaken by those who are well acquainted with the idiosyncrasies of the pigments they are using, otherwise they will only waste time and materials and temper. It will in all cases be found more satisfactory to entrust the printing ink maker with the matching of the pattern.

The proportion of black necessary for the production of subdued colours is very small on account of the fine division and consequent colouring power of the carbon. It will probably not exceed 5% to 10%, varying with the tintorial value of the other pigments. The latter being in great preponderance should be of the best possible quality. Good lakes, i.e., dyes precipitated on an earthy base, such as hydrate of alumina, are most suitable for the purpose. These distribute well, print even, and do not fill up the interstices between the dots forming the half-tones of the block. On account of their strength and bulky nature, such lakes will be found cheaper in the end in spite of their higher price than earth colours. They will save labour m doing away with frequent washing up, and they will not wear the blocks. Excellent lakes of all colours are now produced from aniline dyes, and may with advantage be used where permanency on exposure to light is no object. But if permanency be desired, alizarine lakes made of alizarine, which, like aniline, is a coal-tar product, should be employed. It is also found in nature, as the colouring principle of madder-root, which used to be extensively cultivated in the south of France. Our modern artificial madders are perfectly permanent even in tints, and can now be produced in all shades of red, from scarlet to purple, and in excellent imitations of carmine and cochineal crimson and scarlet lakes. They form a very desirable base for half-tone inks, and should be used by the conscientious printing ink maker for the red in photochromic three-colour printing. More about this later on. Ultramarine is a most undesirable pigment for half-tone inks, as it does not print flat, and it is particularly unsuitable for photochromic printing on account of its opacity.

With these few introductory remarks upon the quality of process printing-inks, I now come to deal with photochromic inks used for three-colour work. The success of photochromic work depends on the blocks, on the inks, on the prmter, and in a certain degree also on the paper. I am going to speak of the ink only, and therefore take it for granted that the blocks are produced by colour-filters constructed on scientific principle, i.e., with a thorough knowledge of spectroscopy and photography, and not chosen in an arbitrary way. I have dealt with this subject in the preceding parts of this book. Further, I must take it for granted that the printer does his part ot the work not in a purely mechanical style, but that he has at least some knowledge of the principles of three-colour printing, the lack of knowledge of which is at present a serious stumbling block in the way of the success of photochromic printing.

One of the crucial tests of good photochromic work is the production not only of a correct rendering of the colouring of the original, but the production of neutral blacks and greys wherever they occur in the original, be it a painting or still-life object. If the colour-filters are correct representatives of the primary colour-sensations of the spectrum, the three negatives or chromograms will be monochrome representatives of the excitations caused on the end organs of our eyes by each of the respective primary colour-sensations reflected from the object. It is necessary in order to obtain a correct rendering of the tintorial representation in print that the positives, i.e., the blocks, should be printed in inks which are complementary colours of the colour-filters used. It is obvious, therefore, that as the colours of the three selective screens, if scientifically constructed, are—if I may use the term—a fixture, so the three pigmentary colours used in printing are also a fixture, and cannot be arbitrarily selected. Here the carelessness, indifference, and ignorance of most printing ink makers has been and is still causing great mischief and bringing ridicule upon one of the most interesting achievements of modern science. I have from time to time examined samples of photochromic inks of various makers, and found they all differ more or less, not only in the shades, but in the strength of the pigments used in their manufacture. Some makers unscrupulously use fugitive aniline lakes for the red, which, after a few days' exposure to light will fade and render the colouring of the whole picture incorrect. The three pigments which alone produce a correct colouring of a picture produced by the photochromic process, are a pure red pigment, one that is neither a purple nor an orange, but is the primary red of the artist, i.e., the combination of fundamental red and blue-violet of the spectrum, as explained before. The yellow ink must be a pure yellow, not inclined either to orange or green, i.e., about the shade of sulphur, or what artists' colourmen call "lemon yellow." The third ink, the blue, must be cyan-blue, somewhat similar to a greenish cobalt blue. Neither the violet nor the green should, however, preponderate in this blue. If these three inks are correctly made, it will, by their mixture, be possible to produce every colour, including tints, saddened hues, and dense blacks.

The tintorial mixture in a photochromic print will be two-fold, optical and pigmentary. Those acquainted with half-tone work know that the shades, tones, and half-tones in a picture are produced by dots of various sizes, the smaller producing the lighter parts of the picture, and the larger the shades and outlines. Now in a photochromic picture, the various colours are produced by the superposition of yellow, blue, and red dots of various sizes. Wl]ere these dots cover each other they produce a pigmentary mixture, almost identically as if the pigments had been mixed by a palette knife previous to being printed. Where these dots lie next to each other they produce an optical mixture, that is, the eye will record two adjoining dots simultaneously, for instance, red and blue appear as violet; blue and yellow as green; red, yellow, and blue, i.e., the three colours combined, as black (or grey if the dots are small and allow the paper to reflect white light through between the interstices).

These remarks now lead us to the second essential quality of the photochromic inks, viz.—transparency. Unless the pigments used are transparent, the pigmentary mixture just alluded to cannot take place. Wherever, for instance, an opaque red dot should cover a yellow one, instead of producing an orange or scarlet it would only show the colour last printed, but if the red is transparent it will combine with the yellow to form orange. It is not very difficult to find a red that answers not only to the required shade but possesses transparency; we find it in madder lake, struck on a transparent base such as hydrate of alumina. This pigment possesses another valuable property, that of absolute permanency when exposed to 46 sunlight. The blue pigment is more difficult to produce. The best is a cyanide blue, which can be made of the requisite shade, and is transparent. It cannot be called absolutely permanent, but the fading when printed full strength is so slight that it need not be taken into consideration. Artists do not hesitate to use this blue in the most valuable pictures. Ultramarine, as I have stated before, must be rejected on account of its opacity, and aniline blues are much too fugitive. The most serious difficulty presents itself in the selection of the yellow and only very recently after a great many experiments I have found a transparent yellow lake which promises well for permanency. It is of the requisite shade and perfectly transparent. Up to now this non-success of producing a permanent transparent yellow necessitated the use of an opaque pigment and printing the yellow first. If that is done it does not matter if an opaque yellow pigment is used so long as it is permanent and of the requisite shade. It is also advisable to print the blue last on account of its possessing the smallest luminosity. But for these two reasons, it would not matter in what order the colours are printed. So it is necessary to print them in the order of yellow, red, and blue. I need hardly mention that it is also of great importance that the pigments should be well proportionate as regards their colouring power. If that is not so, it will be found that the strongest pigment causes the picture to be coloured with a preponderance of that particular colour, which is generally the red. Placed in Lovibond's tintometer it will be found that the yellow and blue pigments are of about equal strength (about seventeen units each), whilst the red pigment, if madder, will measure probably thirty-four units, or about double the strength. It is, therefore, necessary the printing ink maker should proportion the strength of the pigments if correct colouring of the picture is to be expected. This is a matter which I find is almost always ignored.

What I have said about photochromic printing inks will be sufficient to prove that great attention to details is required in the manufacture of these inks. The selection of pigments, suitable not only as to shade but also as far as their permanency, transparency, and tintorial strength is concerned, must be a matter of great care and experience. They require far more care in grinding than ordinary inks, as from this cause variations in shade would cause serious differences in the colouring of the prints.

Although not falling under the heading of "Photochromic Printing Inks," I feel bound to make a few observations about the paper. If you take a pigment — madder lake, for instance — and rub it up either in plain water or gum water, and paint it on a sheet of hard, well-sized, and glazed paper, you will get a bright red, owing to the smooth surface of the paper reflecting some white light with the pigment, making the latter appear bright. Now take a sheet of white blotting paper and paint it with the same colour, the result will be a kind of dirty maroon or claret colour. The blotting paper absorbs some of the light which the glazed paper reflects. The lesson is obvious—use good paper only, hard, well-sized, and glazed, and in printing use hard packing, eight or ten sheets of cream wove paper. It will then not be difficult to print from blocks of very fine grain, and the colours will appear much cleaner and brighter. No pains should be spared, either, in the making ready of the blocks.

Thus with blocks made from scientifically constructed colourfilters, inks of correct hue, good paper, a knowledge of the principles of photochromic printing, combined with a little enthusiasm, which this new scientific way of colour-printing well deserves, we may expect to obtain as good results as are possible at the present state of photo-trichromatic printing.






View of one of the grinding sheds at Caroline Part Works, Edinburgh.

8.12.18

Photo-Trichromatic Printing. Part III. Three-Colour Work. Historical Sketch. Explanation of the principle of the Process. Action of the selective Colour-Filters. Production of the Red, Yellow, and Blue Blocks.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
The old saying "there is nothing new under the sun" may be apphed to three-colour printing". Attempts to produce coloured prints by superposition of the three primary pigment colours were already made in the seventeenth century by German copperplate printers. This method was greatly improved in the eighteenth century by the addition of a black keyblock. It needed, however, the assistance of photography, combined with a better knowledge of chromatics and spectroscopy, such as the end of the nineteenth century brought about, to enable printers to reproduce objects not only in their natural colours but in perfect contour and perspective with only three printings.

J. Clerk-Maxwell first suggested the reproduction of natural colours by the superposition of the three primary colours of light, in a lecture delivered at the Royal Institution on May 17th, 1861.

In 1865 Baron Ransonnet, of Vienna, and at the same time Henry Collen, the Queen's drawing master, had the idea of printing coloured pictures in three colours, by taking photographs of the objects by red, blue, and yellow rays and making superposed coloured prints from the resulting negatives.

In 1868 two Frenchmen, Charles Cros and Ducos du Hauron published a similar idea of producing three-colour photographs. The first treated the matter theoretically, while the latter made practical experiments. They came nearer the true principle, but did not obtain satisfactory results. They proposed to print in red from a negative on which all the coloured rays except red had acted, in blue from another negative on which all the colours except the blue had acted, and in yellow from the third negative upon which all the coloured rays except yellow had acted.

Further efforts were made in 1870 by Professor Husnik, at Prague, and Joseph Albert at Munich, both of which had the assistance and advice of Dr. Vogel, of Berlin, and Dr. Eder, of Vienna. These attempts were more successful although the principle they worked upon was not scientifically correct.

Dr. H. W. Vogel, of Berlin, in 1873, discovered that photographic plates could be made sensitive to various colours. However, for various reasons the application of his discovery did not for some time give the expected results.

Mr. F. E. Ives, of Philadelphia, in 1881, was the first to produce from three letterpress blocks a photochromic picture, using single line screens similar to what are being used at the present time.

Later, Dr. Vogel's son, Dr. E. Vogel, in conjunction with a lithographer, Ullrich, of Berlin, produced photochromic pictures which were exhibited at the German Exhibition in London, in 1891. The system they worked on, however, necessitated the addition of a grey tint, which is not necessary if the process is carried out on strictly scientific principles.

During the last few years Messrs. Husnik & Hausler, of Prague, have produced some beautiful blocks for three-colour typographical work; and quite recently the Heliochrome Company, Limited, 122 Elgin Crescent, Notting Hill, London, have made some splendid blocks for three-colour work.

Before explaining the principles of photochromic three-colour work it should be mentioned that this process is adaptable not only to letterpress work by means of half-tone blocks, but also for collotype and lithography. Collotype gives the most delicate results, but at the same time is the most difficult to work. For commercial purposes the half-tone blocks reign supreme at present.

The principle of photochromic three-colour work is based upon the Young-Helmholtz theory of trichromatic vision. In Part I. it was explained that the colours of all objects can be reduced to three primary colour sensations (red, green, and violet), and with these we can form white light and all possible colours of nature, including tints and saddened colours (or aesthetic shades, as some people like to term them).

Three selective colour filters, interposed between the lens of the camera and the sensitive plates will produce three photographs which when viewed simultaneously through the pure colour filters will stimulate the end organs of our eyes in such a way as to reproduce a mental image of the natural colouring of the object.

On this principle is based Mr. F. E. Ives' marvellous invention, the Photochromoscope. This instrument will produce a mental image of objects in their natural colours and perspective by viewing the three monochrome photographs simultaneously through pure colour filters, red, green, and violet.

To quote Mr. Ives' own words (Journal of Society of Arts, May 27th, 1892): — "By photometric measurement of the density curve of a spectrum negative, the relative amount of action by different spectrum rays may be found. It is therefore only necessary, in order to secure action by different rays in any definite proportion, to use such a combination of sensitive plates and colour screen as will yield a spectrum negative having a density curve corresponding to the graphic curve representing such proportionate action."

The proportionate action of different spectrum rays in the respective negatives would be as indicated in the curves in Koenig's diagram if the green of the spectrum was not itself a compound sensation colour. But for this reason it is necessary for this purpose to regard the purest spectrum green as a primary colour, and make the measurement for density curves accordingly. That is what Maxwell did, and Maxwell's curves, although not the true sensation curves, represent the correct proportionate action for the different rays in the photographic process.



If the sensitive plate was acted upon like the eye, the photographic screens should transmit the various rays in the proportions shown by the form of the respective curves in Maxwell's diagram; but allowance has to be made for the different relative colour sensitiveness of the photographic plates, and for that reason a set of screens that is right for one kind of plate will be all wrong for another. For instance, a yellow screen will give nearly all the action in the spectrum green on an Edwards' Isochromatic plate, and nearly all in the orange-red and yellow on a Lumiere series B plate. It is evident that if one were right, the other must be all wrong. It is obvious that the production of perfect colour filters requires the employment of a photo-spectrograph by an expert. But a close approximation to the best results can be got by using an aurantia screen with a Lumiere series B plate for the negative of the red sensation (printing colour for block, cyan blue), a lighter screen of the same material with a Lumiere series A plate for the green sensation negative (printing colour for block, crimson), and a screen of pale chromium green glass with an ordinary plate for the negative of the blue-violet sensation negative (printing colour for block, yellow).

For the purpose of reproduction by colour printing, positives are made from the negatives which record the three-colour sensations, and from these positives, if we use the typographical method of printing, half-tone blocks are made. Each block is then printed in the transparent pigment colour which represents the combination of the two colour sensations stopped out by the colour filter which was interposed when taking the negative.

As stated in Part II., all colours can be matched by mixtures of the three primary pigment colours, including greys and black. The three primary pigment colours in which the three colour blocks just mentioned should be printed are therefore perfectly sufficient to reproduce the natural colours of any object as far as this is possible by means of the pigments which modern chemistry has placed at our command.

We cannot here enter into the details of making half-tone blocks, neither can directions be given how to make colour filters. Suffice it to say, that some colour filters are made of coloured glass, others consist of glass troughs constructed of two parallel sheets of glass, sealed all round and holding in the intermediate space a coloured liquid. This liquid generally is a solution of an aniline dye of the requisite shade.

Amongst the filters now on sale none are correct as far as I know. Experiments are being made at present to produce sets of colour filters of coloured gelatine and also of glass plates covered with collodion films dyed with aniline dyes. So far, however, none of these are on the market.

The success of photochromic printing in three colours depends of course in a very great measure on the inks, which like the colour filters permit of no arbitrary selection or groping in the dark. Their colours, as no doubt it will have been inferred from what has been explained, are determined by fixed scientific rules. For that reason I thought it fit to devote a separate chapter to the description of the properties of the inks.

Photo-Trichromatic Printing. Part II. Triads.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
The combination of three colours to give an effect which shall be pleasing to the eye is more difficult to manage. Rood recommends at a distance of 120°, or about 20 minutes on our chromatic clockdial, between the three colours. This distance need not be strictly maintained, as will be seen from the following combinations given by Rood:
— Spectral red, yellow, blue.
Purple red, yellow, cyan-blue.
Orange, green, violet.
Orange, green, purple-violet.
Carmine, yellow, green.
Orange-yellow, violet, bluish green.
Scarlet, green, violet-blue. And others.

The combination of triads will always look better if two of the three colours are warm ones and the third cold. One of the warm colours may be a broken one. A warm, pure colour combined with a warm and a cold tint will form a good combination, or two tints with either a pure hue or a saddened colour.

Compared with continental cities, very poor taste is displayed in the colour combinations of the decorations used on festive occasions in this country. Hardly anything but the crude red, yellow, and blue is to be seen. The same may be said of theatrical and other posters displayed more liberally every day on the hoardings. I have seen some posters, printed in America, which showed excellent taste in their combinations of tints and broken colours of various gradations. I trust the few hints given here, which only touch upon the fringe of the subject of colour combinations, may be of assistance to British artists. Letterpress printers seem of late years to display more taste than formerly in their colour combinations in conjunction with some exquisite designs in type and ornamentation. There is, however, plenty more room for improvement in the display of artistic taste, and the scientific theory of colour combinations is well worth a serious study.

7.12.18

Photo-Trichromatic Printing. Part II. Harmony and Contrast.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
Harmony of colour may briefly be stated to exist between two colours which lie very closely together within a few degrees of the chromatic circle, or between two colours of the same hue but of different luminosity, the same hue either diluted with white or broken with grey. A glance at our chromatic dial will make the matter clearer.

To give a few examples: — brown and orange will harmonise, so will pink and maroon, azure and navy blue, azure and pure blue, cream and amber, etc. Neutral grey will harmonise with any colour, although various effects are not equally pleasing. Hard and fast scientific rules cannot be laid down on this subject, which is more a matter of opmion and artistic taste. It may be remarked, however, that neighbouring colours of small interval, and of the same luminosity, should be separated by a neutral grey or black, or one of them should be of a different luminosity from the other.

Contrast colours are hues which are far apart in the chromatic circle, i.e., more than 90° or ¼ hour of our chromatic clock-dial. Rood, also Church, state that colours less than 80° or 90° apart suffer from harmful contrast. Contrast colours more than 90° apart, help each other, and appear more luminous to the eye, although some combinations are not very pleasing but sometimes rather harsh. Scientific rules cannot be laid down for such combination, but only hints may be given. The further apart the two colours are, and the nearer the distance approaches 180°, or ½ hour on the clock, the stronger will be the contrast. When the distance reaches 180° they will be complementary colours. Black and white also form a contrast. Likewise white with broken colours, though these combinations are not always pleasing to the eye. Black will always heighten the apparent luminosity of any colour which is surrounded by it; likewise, in a lesser degree, will grey, whilst white will lessen the apparent luminosity.

6.12.18

Photo-Trichromatic Printing. Part II. Chromatic Clock Dial.





Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896

It will be useful to artists, colour printers, decorators, and, in fact, to all who work with colours, to remember which are contrast or complementary colours, as the case may be, and how to produce certain saddened colours or tints which may be required. As everybody is almost sure to have a watch or clock near at hand, it occurred to me that the clock face might be turned into a useful chromatic circle, and if once the position of the pure and broken colours be committed to memory, which should not be a very difficult feat, they may easily be called to mind in their proper position relative to the figures on the clock. I have taken Rood's excellent contrast diagram for a guide, but found it necessary to slightly modify the position of the colours so as to make them correspond more readily with the figures on the clock-dial, and to be remembered more easily. My chromatic clock-dial is intended more for practical every-day use than for scientific purposes.

I placed yellow, being the most luminous colour of the spectrum, at the top at XII. of the clock, and as we proceed downwards to the right, the colours lessen in luminosity till we reach VI. (ultramarine blue), thence as we proceed upwards to the left through violet, purple, etc., the luminosity again increases till we reach yellow, our starting point.

Outside the pure hues I have placed the saddened colours, which may be produced by decreasing the luminosity of the pure colours, i.e., by the admixture of neutral grey pigments, whilst inside I have placed the names of the tints which may be produced by adding white to the pure hues.

5.12.18

Photo-Trichromatic Printing. Part II, Pigment Mixtures: Primary Pigment Colours. Secondary Colours. Black and Grey. Tertiary Colours. Saddened Colours. Tints.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
Many of the readers of this booklet, who have followed the brief outline of the principles of chromatics and particularly the explanation of the Young-Helmholtz theory of colour vision, will probably ask themselves if the scientists who call
RED, GREEN AND VIOLET
primary colours, have wiped out of existence the notion of the three primary colours of the artists
RED, YELLOW AND BLUE.

This, however, on closer examination we shall find is not the case. Let us first remember that the scientist deals with coloured light, and in making mixtures adds one light to another, whilst the artist, by the superposition of pigment colours (if transparent), takes away more and more of the light reflected from the white surface on which he works.

The scientist defines as primary colours those which cannot be produced by the mixture of any two colours of light, and which on the other hand cannot be further disintegrated. We must also recollect that if the three primary colours—red, green and violet—be combined in suitable proportions, they produce white light.

It will be remembered that any colour sensation other than the primaries may be produced by mixture of two of the primary colour sensations in suitable proportions, with or without the addition of a certain proportion of white.

The artist calls primary colours those which cannot be produced by superposition of any two transparent pigment colours. If the three primary pigment colours, red, yellow, and blue, be mixed in suitable proportions, they will produce grey to black, according to their density. Any colour may be matched by mixtures of two or three of the primary pigment colours, or by mixing two primary colours with a proportion of grey (i.e., diluted black) or white.

The artist calls secondary colours mixtures of two primary pigment colours. These secondary colours are supposed to be complementary colours of that primary colour which has not entered into the combination that makes up the respective secondary colour. This statement is, however, not strictly correct, as can be proved by experiment. The secondary colours of the artist ought rather to be called contrast colours of their primaries. For an explanation of the term complementary colours, refer to the first part of this book. The secondary colours of the artist are the primary colours of the scientist, red being obtained by superposing the transparent pigment yellow upon the transparent pigment red (a bright crimson), green by superposing the transparent pigment blue (cyan blue) upon the yellow, and blue-violet by superposing the bright crimson upon cyan-blue.

It is, therefore, evident that although red seems to be common to both scientists and artists as a primary colour, the primary red of the scientists, i.e., the fundamental red of the spectrum, is quite different from the primary red of the artist. The fundamental red of the spectrum is similar in hue to vermilion, or, perhaps, a bright scarlet lake as made up by some artists' colourmen. This red produces good orange when mixed with yellow, but mixed with blue it produces only a dirty looking violet. It will also be impossible to produce a crimson by mixing small proportions of blue with vermilion, but scarlet can successfully be mixed from yellow and crimson lake (if the latter is not too purple). Let us take crimson lake in place of vermilion for the purpose of mixing violet, and we shall see that it produces a satisfactory violet, with cyan blue. We see now that crimson makes with yellow equally good orange as it produces good violets when mixed with blue, and that we cannot produce crimson by any mixture of two pigment colours. We, therefore, are justified in terming crimson a primary pigment colour. The correct shade of this crimson will scientifically be determined by a mixture of the red and blue-violet rays of spectrum, i.e., all the spectrum colours minus the green sensation. The crimson lake of some of the leading artist's colourmen is a very fair representation of this primary red of the artists.

Using familiar terms, we may call the primary red of the scientist, "scarlet," and the primary red of the artist, "crimson."



The primary yellow of the artist may be defined as a combination of the fundamental red and the fundamental green of the spectrum, i.e., all the spectrum rays minus the blue-violet. The representative amongst pigments is what artists usually term "lemon yellow," a mixtureof chromate of zinc and chromate of barium, and which printers usually call "primrose yellow." Pale cadmium yellow also is of the same hue. This colour will produce good orange in combination with crimson, i.e., the primary red of the artist, and good greens with- cyan-blue (not violet-blue, such as ultramarine).

The primary blue of the artist may be described as the combination of the fundamental green and the fundamental violet sensation of the spectrum {i.e., all the spectrum rays minus those of the red sensation). This is represented by some kinds of Prussian blue (ferric ferro-cyanide of potassium). Captain Abney, to dispel this confusion of primary colours of light and primary transparent pigment colours, has proposed that they shall be indicated by plus and minus terms. Thus, spectrum red is + R, spectrum green is + G, and spectrum violet is + V; whilst the primary pigment red (crimson) is — G, the primary pigment yellow (primrose) is — V, and the primary pigment blue (cyan-blue) is — R.





We have seen in the first part of this booklet that blue and yellow light produce white light, whilst the artist when mixing blue and yellow pigments produces green. How can this difference be explained? The fact is that the yellow pigment transmits both green and red, whilst the cyan-blue pigment transmits both violet and green. The green is, therefore, the only colour which both pigments transmit, and is the residual colour when they are superposed.

The colours nearest the caloric end of the spectrum, the red and orange, will give us a sense of warmth, as will, likewise, their pigmentary representatives. Yellow, which forms the most luminous part of the spectrum, gives us a sense of light. A slight wash of gamboge over some parts of a water-colour landscape will produce a sunlight effect.

The colours nearest the "actinic" part of the spectrum, the green blue, and violet, produce a sense of cold.

Hence, when we hear artists speak of warm and cold lights and shades, warm and cold greys, we may infer that in the warm lights, shades, and greys, the red or orange preponderates, whilst in cold lights, shades, and greys, the green, blue, or violet preponderates.

It has before been stated that crimson, yellow, and cyan-blue transparent pigments, mixed in suitable proportions, produce black, or if diluted with white a grey will result. Grey may also be defined as white deprived of part of its luminosity. All the constituents of white light are partly and equally absorbed by the body we term grey. A black pigment diluted with white will give a similar effect.

If we mix crimson, yellow, and cyan-blue to produce black, it will be found almost impossible to mix the pigments so that a perfect dead black should result, that is, a black that will absorb all the white light (except, perhaps, the slight percentage which all blacks reflect). It will be found that our mixture, and also most of the carbon blacks, reflect a little orange or yellow besides this small percentage of white, and this orange or yellow will appear brown to the eye. The artists' colourmen and the printing ink makers are well aware of this fact, and try to counteract it by mixing a small proportion of blue with the black.

Instead of diluting his black with white to make a grey, the watercolour artist utilises the transparency of his pigments, which allow the paper to reflect white light throught the paint.

There are colours which are widely spread in nature, and are well represented by pigments, which are not seen in the spectrum but can only be imitated by partly abstracting luminosity. These colours are maroon, russet (terra-cotta), brown, citrin, olive, sage, myrtle, navy-blue, slate, and plum colour. These are broken hues and many people like to call them "art shades." They may be obtained by mixing pure colours with varying proportions of neutral grey. They are often called "tertiary" colours from the erroneous notion that prevails amongst artists that they can only be made up by mixing two of the "secondary" colours. A little reflection and experimenting will show that by mixing two "secondary" colours we really bring together the three primary (pigment) colours in more or less equal proportions, making up a black or grey which saddens the mixture of the two remainmg predominating colours. Thus we have accomplished, by a roundabout way, what can be done more directly by mixing grey with pure primary or secondary colours as the case may be. Another way of stating the matter is that saddened colours are hues deprived of their luminosity.

Saddened red is called maroon.
" red-orange " brown.
" orange-yellow " russet or terra-cotta.
" yellow " citrin.
" yellow-green " olive.
" green " sage.
" blue-green " myrtle.
" blue " navy blue.
" violet " slate.
" purple " plum.

If we dilute pure hues with white we get tints which are also called by familiar names as follows: —
Diluted red is called pink.
" orange-red " salmon.
" orange " buff.
" orange-yellow " cream.
" yellow " straw.
" green " pea green.
" blue-green " sea green.
" blue " azure.
" violet " lavender.
" purple " heliotrope.
" purple-red " magenta.

We may also mention two more familiar colours: —Drab, which is a grey in which orange slightly predominates, and French grey, in which blue slightly predominates.

4.12.18

Photo-Trichromatic Printing. Part I. Complementary colours.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
Complementary spectrum colours are any two colours which, when combined, will produce white light. This can be brought about by suitable means, such as, for instance. Clerk-Maxwell's colourbox or Captain Abney's colour patch apparatus. Such pairs of complementary colours are purple and green, red and bluish-green, orange and blue, yellow and violet, etc. Such pairs, if combined, produce white light, and are therefore called complementary colours.

It may here be stated that the primary colours and their secondaries of the artist's pigment-colours are not really complementary, but "contrast colours." These will be fully dealt with later on.

On these demonstrable facts the Young-Helmholtz theory of colour vision is based. This famous theory, which is now usually accepted as the best working hypothesis, briefly declares: —
* Dr. D. Fraser Harris on Ives' photochromoscope, in a paper read before the Philosophical Society of Glasgow, Nov. 6th, 1895.
  1. *That there are three primary spectrum colours, red, green, and violet, which cannot be produced by any mixture of any other colours.
  2. That there are three sets of "end-organs" in the retina of our eyes, one set being powerfully stimulated by red and orange rays, less so by green, and least of all by blue-violet; the second set being especially excited by green light, and less so by the spectral rays on either side of it, i.e., red and violet. The third set are most susceptible to violet light, less so to green, and least of all to red.
  3. That by stimulation of all three sets of "end-organs" (rods and cones) in nearly equal intensities we perceive white.

The relative power of different spectrum rays to excite the respective fundamental colour sensations is shown by the curves in Koenig's diagram (modified and corrected by Captain Abney), which may be taken as the most correct.



The fundamental green sensation cannot be perceived by the normal eye, but only by red or violet colour-blind people, for the reason that the red and violet sensations overlap in the green of the spectrum, as will be seen in the diagram of Koenig's curves. The colour-tone of the fundamental green sensation as purely as a normal eye can see it, is located between the Fraunhofer lines E and b, and may be taken as the primary green for purposes of colour mixture.

The best representation of the fundamental red sensation lies between the lines C and D, nearer the former by two-thirds of the distance, and may approximately be represented by vermilion with a slight tinge of carmine.

The best representation of the fundamental violet sensation lies between the G and H lines of the spectrum, and may be represented by deep ultramarine, which has been tinged with methyl violet dye.

There are rays beyond the red and beyond the violet end of the visible spectrum. Those beyond the red end, the infra-red rays are caloric or heat rays, given out by heated bodies before they show incandescence, and these can be measured by an instrument called a thermopile. The rays beyond the violet end of the visible spectrum are called the ultra-violet or "actinic" rays.

The complete spectrum consists of the invisible infra-red (heat) rays, the visible rays, and the invisible ultra-violet rays. These three parts are of about equal length. To the artist and colour printer however, only the middle, being the visible part, is of value.

For the exact definition of a colour, three qualities have to be determined. The qualities are called colour constants, and are the following: — Hue, luminosity and purity. Hue is often called "tone."

Hue is what in every day language is called the colour, for instance, scarlet, crimson, violet, etc. For scientific purposes the hue is referred to its proper location in the spectrum.

Luminosity means the brightness with which a colour appears to the eye compared with a white surface, which is illuminated simultaneously by the same white light.

Purity means the freedom of a colour from admixture with white light. Tints reflect a great proportion of white light, and are diluted or impure colours. Pink is an impure crimson red, lavender is an impure violet.

3.12.18

Photo-Trichromatic Printing. Part I. The three fundamendal colour sensations.


Photo-Trichromatic Printing
C. G. Zander
Published by Raithby, Lawrence & Co., Ld., Leicester
1896
The theory of the three fundamental colour sensations originated with Dr. Thomas Young in 1802, but was discredited and forgotten until 1853, when Prof. Helmholtz again brought it forward, and by his experiments added greatly to its probabilities. Soon after, J. Clerk-Maxwell first demonstrated pretty conclusively, by means of an ingenious contrivance of his own, called Maxwell's colour box, that there are really only three fundamental or primary colour sensations namely, red, green and violet.

If colours representing these three fundamental sensations are combined in proper proportions they form white light. Red and green combined form yellow. Green and violet combined make blue. Violet and red make purple, a colour not present in the spectrum.

Yellow (the combination of red and green) and blue (the combination of the violet and green) combined in proper proportions will also produce white light.

To call red, green and violet "primary" colours may seem strange to those who are used to the primary colours of the artists, namely, red, yellow and blue, and knowing what effects their various combinations will produce. However, what I have just stated about coloured light (for we are not now dealing with pigment-colours) can be proved, though perhaps not in the most strictly scientific way, by having three coloured circular glass slides to match, as nearly as possible, the red, green and violet of the spectrum. White light is projected throug-h these slides on to a screen by means of a lantern, and the coloured light discs moved until they partly overlap, as shown on the frontispiece. This experiment was shown upon the screen by Mr. F. E. Ives in his paper on the photochromoscope, read before the Royal Society of Edinburgh on January 17th, 1896. The outer parts of the circles will show the fundamental red, violet and blue, the centre where all three overlap will be white or probably slightly grey owing to the impure colouring of the glasses. Where the red and green overlap yellow will be shown, where green and violet overlap cyan-blue, and where violet and red overlap a kind of pale crimson or magenta.

2.12.18

Photo-Trichromatic Printing. Part I. Chromatics.

Colour has no material existence; it is a sensation caused by the excitation of the nerves of the retina of the eyes.

According to the Undulatory Theory of hght, the molecules of luminous bodies are supposed to be in a state of exceedingly rapid vibration and to communicate these vibrations to the ether, that highly rarefied substance, which is said not only to pervade all space, but also to surround the molecules of all matter. These vibrations or waves of the ether are exceedingly rapid and minute, the wave-length varying with different coloured lights. The length of the rays which excite the sensation of red, is about 1/39000 of inch, whilst the length of the rays which excite the sensation of violet is about 1/59500 inch. Orange, yellow, green and blue are of intermediate lengths between the two. The velocity of light is 186,772 miles per second.

To obtain an idea of the principle of the wave motion of light in the shape of a homely illustration, take a rope, perhaps ten feet long or longer, tie a number of knots in it and fasten one end to the knob of a door. Hold the other end in your hand and give it a rapid up and down motion. A wave-like motion will run from your hand along the rope to the door knob and the knots will move transversely to the direction of the vibration, but will practically maintain constant distances relative to one another, or to any fixed points such as your hand or the door knob.

Another way of illustrating the wave-like motion of light is to fill a basin with water and strew it with a little sawdust. When the water and sawdust are perfectly still, drop a pebble or some other heavy body into the water. You will notice that concentric rings or waves spread or run from the place where you dropped the body in. This wave-like up and down motion of the water will be communicated to the floating particles of sawdust, which here serve to mark the positions of the particles of water. These particles, when the agitation has passed, will have come to rest in precisely the same places where they were before. They will neither travel nearer the edge of the water nor nearer the place where the pebble was dropped in.

The rapidly vibrating molecules of an incandescent body set up corresponding vibrations of the ether, and these wave-like movements spread in all directions, or as scientists call it, in concentric spheres. The particles of the ether move transversely to the path of the light as we have seen in the movements of the knots in the rope or the floating sawdust agitated by the water.

If a ray of sunlight be permitted to pass through a small hole (or better, a narrow slit) in the shutter of a darkened room, and to pass through a prism—a triangular piece of glass—held in the beam, the ray of light will be spread out or dispersed, and on the opposite wall of the room a band of colours, as in the rainbow, will appear. These colours in their order are red, orange, yellow, green, blue, and violet, and they are called the colours of the spectrum. Sir Isaac Newton named the dark portion of the blue, where it merges into violet, "indigo," thus counting seven colours—the reason why we often hear or speak of "the seven colours of the rainbow." This experiment teaches us that white light is made up of many coloured rays, into which it can be disintegrated. Colour, therefore, may be taken to be a part of disintegrated white light. We shall see further on that coloured rays may be united again to form white light.




A darkened room and a slit in its shutter is a very cumbersome arrangement, and useless for the exact scientific analysis of light. For this purpose an optical instrument, called a spectroscope, has been devised.



A large laboratory spectroscope usually consists of three movable tubes, arranged at angular distances of about 120° (or the third of a circle) from one another: in the centre of the circle is placed the prism. The collimating tube allows light to enter through a narrow adjustable slit and pass through a lens called the collimator, which causes the rays of light to fall parallel upon one or more prisms. These prisms bend or refract the light and break it up into its component parts or colours, which can be viewed through another tube, which is really nothing but a modified telescope. The best spectroscopes have yet a third tube, containing an engraved or a photographic scale, which can be seen through the observing telescope, simultaneously with the spectrum — a contrivance most helpful in spectrum analysis. Spectroscopes vary in their arrangements, but the principle upon which they are constructed is the same. A smaller and more convenient form of spectroscope is called a direct vision or pocket spectroscope, and contains slit, collimating lens, prisms and telescope all in one tube, which can be drawn out for focussing purposes.



If we view the spectrum of sunlight or the "solar spectrum," as it is called, we see a number of gaps or dark lines across the band of colours. These lines will always be found in the same position relative to the colours and alwa3's at the same relative distance from each other, and are, therefore, used as convenient landmarks. They were first described by the famous physicist, Dr. Wollaston, in t8o2. Fraunhofer minutely investigated and mapped them out in 1814, and they have ever since been called after him, Fraunhofer's lines. The principal lines are denoted by ten letters:—A, a, B, C, D, E, b, F, G, H. A and a are in the dark red end of the spectrum, B and C in the red, D in the orange-red, E and b close together in the green, F in the blue, G in the blue violet, and H at the violet end of the spectrum. Only the solar spectrum shows these Fraunhofer lines, which are due to the absorption of some wave lengths of light by gases in the sun's envelope.

Electric, lime and gas-light, and all luminous solid and liquid bodies, give continuous bands of colours or spectra. Glowing vapours and gases do not show continuous spectra, but only bright lines on a dark background. These lines are different and characteristic for different substances, bemg always exactly the same for each chemical element. They have been carefully observed and mapped out, and form the basis of what is called " spectrum analysis."

If light emitted by an incandescent body passes through a gas, a negative spectrum will result. The spectrum will then show dark lines in precisely the same places where the bright lines would appear on a dark ground, if that particular gas were itself in a state of incandescence.

"The spectrum method of analysis is distinguished from ordinary chemical methods by its extreme delicacy. The three-millionth part of a milligramme of a salt of sodium, an imperceptible particle of dust to the naked eye, is yet capable of colouring the flame yellow and of giving the yellow line of sodium in the spectroscope. More than two-thirds of the surface of the earth are covered by sea, which contains sodium chloride or common salt. When waves are raised by the storm and their foaming summits are carried away, fine particles of salt are mingled with the air and carried far over the land; common salt is consequently distributed through the whole atmosphere in the form of a fine dust. On account of this almost constant presence of sodium chloride, it is scarcely possible to obtain a flame which does not exhibit the yellow line of sodium. It is only necessary to strike a handkerchief upon the table, or to close a book sharply, to make the dust which escapes, colour the adjoining Bunsen's flame yellow, and to make the sodium line appear m the spectroscope." (Lommel, "Optics and Light," page 152.)

If a piece of ruby glass is held in front of the slit of the spectroscope, all the colours of the spectrum disappear, except the red and orange. This effect shows that the ruby glass stops or absorbs the violet, blue and green rays of white light, and transmits only part of the yellow or orange and the red rays. If a green glass be taken instead of the ruby one, it will be found that the red and orange on one side and the blue and violet on the other side of the spectrum are blotted out or absorbed. The remaining part, which is green in this case, is called an absorption spectrum.

When a ray of light strikes a solid body, it is supposed to penetrate through a minute distance, and to leave again at an angle similar to that described by a billiard ball striking the cushion and rebounding. This angle is called the reflecting angle, and is subject to fixed laws, the laws of reflection, which, however, cannot be defined here. It may, however, be briefly stated that a polished surface, such as a plane mirror, reflects the light regularly, keeping the rays closely together or parallel, whilst rough surfaces, such as snow or white paper, scatter the light in all directions.

If white light illumines a body and all of it is again reflected, the body will appear white. If all the light is absorbed, the body will appear black. Snow reflects all the white light and therefore appears white; black velvet absorbs all and appears a perfect black. A sea fog, which diffuses all .the white light, will probably form the purest white in nature.

If part of the coloured rays constituting white hght are absorbed and part are reflected, the body will appear coloured. The colour of the body is determined by those constituents of the white light, which being reflected, enter our eyes and excite certain changes in the "end-organs" of the retina. The remaining constituents of white light are retained or extinguished by the body.

A red poppy will retain some constituents of white light, namely, violet, green and yellow, while it will reflect orange and red, which two reflected colours will give the poppy its characteristic scarlet appearance. A bunch of violets will absorb all the rays of white light except blue and violet.

The colour of a body will be modified by the kind of light to which it is exposed. Let a poppy be exposed to light passing through a green glass, and it will appear black. This is caused by the red and yellow rays, which the poppy reflects under ordinary circumstances, being stopped by the green glass, whilst the poppy does not possess the property of reflecting the green which the glass transmits. No light at all will, therefore, be reflected from the poppy, nor excite our optic nerves under these peculiar circumstances, and the result is blackness. A printer viewing a pale yellow print through a blue glass will, from the same cause, see the yellow print as if it were printed in black. Gas-light, which is deficient in violet rays, will modify most colours, particularly violet.