A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)For convenience in application dyes are grouped according to properties which are common to certain dyes causing them to be applied by similar methods. Thus the dyer finds it convenient to group dyes as acid, basic, mordant, direct cotton, vat or sulphide dyes without regard to the chromophore groups or the relations between colour and constitution.
The chief use of colouring matters is for the decoration of textile fabrics and the chief methods of application may be briefly stated in reference to the main uses.
Acid Dyes. This class is composed entirely of coaltar dyestufls, except for the natural dyestuff, cudbear and orchil. They are mostly sodium salts of coloured organic acids, e.g., sulphonic acids, carboxylic acids and nitrophenols. They are put on the market as powders containing sodium sulphate or chloride and often sodium carbonate. The system of diluting to type with these materials in order to maintain a standard article on the market easily lends itself to adulteration for the purpose of producing an apparently cheaper dye powder. The valuation of a dye sample may be accomplished by comparative experimental dyeing under conditions similar to those employed in practice. Where the constitution is known many dyes may be estimated by means of titanous chloride (Knecht). Spectroscopic analysis of dyes for purity, mixtures, etc. according to the method of Fprmanek is in restricted use owing to limited data and the expensive apparatus required. Different brands of the same dye are often obtained by grinding in a small amount of a shading-off colour to modify the shade for trade purposes as a distinct product. This may be extended to the production of mixtures of primary colours, etc. to give any desired shade. Many dyes for union materials are mixtures of this type, e.g., acid dyes dyeing well from neutral baths and direct cotton dyes. Such a mixture will dye a wool and cotton union in a single dyebath. The detection of such mechanical mixtures is done by blowing a puff of the dye powder on to a filter paper wetted with water, alcohol, etc. and examining the colour of the dissolving specks of powder. Or use is made of differences in diffusibility by dipping filter paper in a solution of the dye and examining different zones of colour formed above the surface by capillary attraction (Goppelsroeder).
More rarely acid dyes (so-called) are found containing metallic salts, as for instance those of chromium, copper, magnesium, zinc, etc., where these produce some desired modification in properties, as in the case of acidmordant dyes.
The application of acid dyes to animal fibres (wool, mohair, etc., silk and wild silks) is from hot acid baths. Example. Medium shades of colours are obtained on wool with 2 per cent, of its weight of dye, 2 per cent, of sulphuric acid and 10 per cent, sodium sulphate in a bath equal to thirty times the weight of wool. The acid aids dyeing and may be replaced by formic acid, acetic acid or ammonium acetate where there is a liability to dye unevenly or to change shade. The sodium sulphate assists, in the production of level shades and is increased where a tendency to unevenness is to be counteracted. About 5 per cent, dye is required to dye blacks. Certain acid dyes are applied according to special methods.
Acid dyes have no affinity for cotton but may be applied by padding and drying the dye on the fibre, giving shades fast only to light.
The fastness of acid dyes on wool varies, but on the whole is good to common agencies, e.g., light and washing, and these dyes are considerably used on dress materials, carpet yarn, and various unions containing wool, also on silk fabrics.
Basic Dyes. This class contains the brightest and strongest colouring matters. They are mostly hydrochlorides of coloured bases, e.g., Magenta, Methyl Violet, etc. The only well-known natural dye of the basic class is berberine (barberry), now hardly ever used. The purer types of certain basic dyes appear on the market as crystals, e.g., Diamond Magenta, Malachite Green crystals. Dextrin is sometimes present as an adulterant in powders. The basic dyes dye animal fibres direct from aqueous solution. Restraint on the dyeing is secured by a slight addition of acid. Example. A medium shade of most basic dyes is obtained on wool by applying 1 per cent, dye with ½ per cent, acetic acid from a bath 30 times the weight of the wool being dyed, with ½ hour's heating to 95°C. and ½-1 hour's heating at 95°C. A medium shade on cotton is obtained by first mordanting the cotton in a cooling bath of tannin (3 per cent.) followed by fixing the tannin with a cold bath of tartar emetic (1½ per cent.). Auramine is dyed not higher than 80°C. as it decomposes at temperatures near the boil. Acid mordants other than tannin may also be used, e.g., oil mordants. The fastness of basic dyes is inferior to that of acid dyes, and on that account their use is restricted mainly to the production of bright shades unobtainable with other classes of dyes, and to the "shading-off" or "topping" of shades dyed by other methods.
Direct Cotton Dyes, Substantive or Salt Dyes. These dyes are acid colours having a special affinity for cotton, except a small class of strongly basic dyes, e.g. the Janus dyes, which dye cotton direct. Most of them are derivatives of benzidine, but many other products are known which will dye unmordanted cotton. The only well-known natural dye of this class is turmeric, which is no longer used to any large extent for dyeing. They are sold as powders, usually containing sodium sulphate or chloride and sodium carbonate. When dyed from a neutral or slightly alkaline bath the dye is taken up as a whole, i.e. the sodium as well as the colour acid, hence the name Salt Dyes. They are mainly used for cotton and cellulose fibres, but certain of these dyes also find application to animal fibres, in which case dyeing may be done from a slightly acid bath. Example. For a medium shade 2 per cent. Benzopurpurine may be dyed on cotton from a batli twenty times the weight of the material, containing 10 per cent, sodium chloride or sulphate and 1 per cent, sodium carbonate. The cotton may be entered cold, raised to near the boil in half an hour and maintained for half an hour at this temperature.
The fastness of these dyes is generally good to usual agencies, but in many cases may be considerably improved by a suitable treatment after dyeing (see page 160). They are used for all ordinary purposes on cotton, in calico printing, on linen, ramie, paper, wool and silk. The natural direct dyes turmeric and annatto are fugitive.
Mordant Dyes. These colouring matters possess a special acid character enabling them to form insoluble lakes with metallic mordants, such as salts of tin, aluminium, chromium, copper, iron, etc. The colour of the lakes given by any one dyestuff and different mordants may vary widely, tin giving the brightest shades and iron the dullest. Fastness to various agencies also varies with the mordant used, e.g., iron and copper are noted for giving shades fast to light, but shades on iron mordants are liable to be not so fast to acids as on chrome mordants, which again are noted for fastness to washing and are mostly used on wool. The bright shades on tin and alum mordants are not nearly so fast to light or washing as the shades produced by use of chrome.
The substituent groups giving mordant dyeing properties are OH, COOH and NO. According to rule (Liebermann and Kostanecki) two of these groups must be present in a dyestuff, ortho to each other, to give mordant dyeing properties. There are, however, many exceptions to such a statement, although mordant dyes in general comply with it. In the azo series dyes having mordant dyeing properties are found containing only one OH group, ortho to the azo group. It will be seen that dyes complying with other conditions of grouping and application may also in addition possess mordant properties, thus there are Acid Mordant Dyes and Salt Mordant Dyes, which are faster when fixed with chrome than when merely dyed as Acid or Salt Dyes. At the same time chroming always affects the sliade more or less. Such products are soluble in water, whereas the mordant dye per se is rarely very soluble. The latter are put out as 20 per cent, pastes, dyeing being done with the colouring matter in suspension. Water soluble (s.w.) brands of these dyes are often produced by the action of bisulphite on ketonic dyes, e.g. alizarines. With these products care is taken to control the temperature during dyeing so as to avoid rapid decomposition in the bath. Example. Wool is boiled for 1½-2 hours with 3 per cent, bichrome (K2Cr2O7 or Na2Cr2O7, 2H2O) and 2½ per cent, tartar in a bath thirty times the weight of the wool. It may then be dyed similarly witH5 per cent. Anthracene Brown paste, in a bath of similar volume containing 1 per cent, acetic acid.
Most dyes of this class are polygenetic
, i.e., give different shades with different metallic mordants.
Cotton may be mordanted with Turkey Red Oil by steeping and drying when it will then take up alumina. Or acetates of alumina, chrome, or iron, may be steamed on the cloth and the combined acetic acid driven off, the alumina or other hydrate being then combined with oil. Acid mordant dyes may be first dyed on wool like acid dyes and then after-chromed, In some cases, chrome compounds may be present from the start, e.g. Metachromé dyes.
The chief natural dyes in use are of the mordant class. The good properties of certain yellow dyes such as fustic, weld, quercitron bark and Persian berries have prevented their entire disuse.
The redwoods, cochineal, and logwood are other natural mordant dyes in extensive use. Ready prepared extracts of these products are often used for dyeing, e.g. Flavin, Fustin, Ammoniacal Cochineal, Logwood Extract and Haematein Crystals. The methods of dyeing with these products are not essentially different from the methods of applying artificial mordant dyes. Logwood or Haematein is dyed on a chrome, iron or copper mordant, each mordant being characterised by different properties of resultant shade and fastness, these being functions of the nature of the lake formed on the fibre. Cochineal is usually dyed with a tin mordant in the dyebath, oxalic acid being added to prevent lake formation in the bath. Other dyes are first dyed and then "saddened" with a mordanting salt in a similar way to the after-chroming of an acid-mordant dye, after first dyeing on wool as an acid dye.
Vat Dyes. Indigo is the chief dye of this class, and until comparatively recently was the only dye of the type in use. The vat dyes are stable insoluble colouring matters which by reduction, as for example with hydrosulphite of soda, zinc dust, glucose, etc. along with alkalies, give solutions of their leuco compounds from which they may be dyed on cotton and also wool and silk, if the alkalinity of the dyebath is not required to be such as would injure animal fibres. Indigo is also dyed from fermentation vats, reduction being effected by the aid of micro-organisms. The true shade is not developed in vat dyeing until the material is removed from the vat liquor, and the leuco body taken up by the fibres re-oxidised to the colouring matter, either by air oxidation or an oxidising agent. The stability and insolubility of vat dyes also afford some measure of their permanency when applied on textile materials, but it should be remembered that a vat dyestuff need not inevitably be fast, and although the highest degree of fastness is attainable by the use of dyes of this class there are others which are by no means fitted for production of the fastest shades.
The quantities of hydrosulphite and caustic soda required vary with different dyes as does also the temperature of dyeing.
Sulphide Dyes. These are dyed in the reduced state from alkaline baths containing sodium sulphide which acts both as reducing agent and alkali. Sodium carbonate is frequently added also to increase the alkalinity and common salt is added to aid the dyeing. Owing to the alkalinity of the bath the use of sulphide dyes is almost entirely restricted to vegetable fibres which are usually dyed at or near the boil. The full shade only develops by subsequent oxidation with air or oxidising agents, of which bichrome and peroxide are most in use.
Dyes produced on the Fibre. This class includes Aniline Black, Para-Red, Nitroso-Blue and a few Mineral Dyes, such as Iron Buff, Prussian Blue, Chrome Yellow and Manganese Bronze. These latter are produced on the cotton fibre by successive paddings or steeping, followed by squeezing-off and immersing in a reagent to develop the mineral colour. For example, if cotton is steeped in basic lead acetate and then in bichromate of potash, insoluble lead chromate or Chrome Yellow is formed on the fibre. It is not suitable for wool owing to the sulphur in the fibre. Mere steeping in a solution of permanganate causes the deposition of brown manganese hydroxide on cotton or animal fibres, e.g., furs, the tips of which may be discharged white by brushing with bisulphite of soda. Prussian Blue is produced on wool by heating in a bath of potassium ferrocyanide and sulphuric acid.
The dyeing of silk is often done in a bath containing "boiled-off liquor" kept over from the removal of gum from raw silk with soap.
The dyeing of leather is on similar principles to the dyeing of wool, acid and basic dyes being mainly used. Certain basic dyes find their main use for this purpose, e.g., Phosphine.
The dyeing of skins and furs is done after degreasing. Acid or basic dyes are used and also colours produced by oxidation of amidophenol.s or diamines, e.g., with peroxide, these latter giving brown and black shades. Feathers aVe usually dyed with acid dyestuffs in an acid bath.
As regards vegetable fibres, linen is dyed like cotton, but penetration is slower. The same applies to ramie (rhea) or China grass. Hemp is mainly dyed with basic dyes. Fibres containing lignin dye full shades with basic dyes without a previous mordanting with tannin, e.g., jute, cocoanut fibre. Straw and wood chip are commonly dyed with basic or acid dyes, but also more and more with direct cotton dyes in boiling baths containing Glauber's salt. Basic and acid dyes are also used largely for paper staining; perhaps most success is attained by adding a basic dye to the pulp first and then an acid dye when the dyes mutually fix each other. Direct cotton dyes are in use on better class paper and to some extent sulphide dyes, but the application of the latter is not easy.
The dyeing of wood, vegetable ivory, etc. follows the dyeing of wood chip in principle. It may however be done under pressure to obtain better penetration.
The fat or oil colours, which are soluble in oils, benzoline, alcohol, etc., are made from basic dyes by conversion into oleates, stearates or resinates; for example dissolve in 100 parts of hot water 1,25 parts of Methyl Violet and 5 parts of good soap. When cold add 2,5 parts of hydrochloric acid. The precipitated fat colour is collected, melted and the solid fat layer removed. Resinates may be prepared in a similar manner. Solutions of these fat colours in benzine are used in dry dyeing, and most of the colour manufacturers put out fat colours ready made. Oil colours are also used in boot polishes. For the colouring of fats and oils Nigrosines and Sudan colours are largely used. Dyes of this type are usually soluble in alcohol or methylated spirit, and along with many watersoluble basic dyes, which happen to be spirit-soluble also, are used for colouring varnishes and lacquers. In ink making basic and acid dyes are largely used, e.g., Methyl Violet, Eosine, etc. Gall inks are often shaded with acid dyes. Both acid and basic dyes find employment also in the colouring of soap, the dye being added to the kettle if it will stand boiling with alkali, if not it is added in subsequent mixing.
The production of pigments is an important branch of the colour manufacturing industry.
Acid and basic dyes are very largely used for production of lakes for wall-paper printing, coloured paper, textile printing (e.g., with albumen as fixing agent), for water colours, crayons, sealing wax, etc.
The lakes are produced by precipitating dyestuffs on to suitable bases, for example, barytes or heavy spar, aluminium hydrate, Blanc Fixe (precipitated barium sulphate) and for basic dyes white china clay or green earth. As precipitating agents barium chloride for all acid and most direct cotton dyestuffs, lead salts for Eosines. tannin and resin soaps for basic dyestuffs.
The choice of base or carrier is often more important than that of the dyestuff. For lakes of good covering power to be used in painting witli oil or spirit varnish, lead sulphate, zinc white, Lithopone (a mixture of barium sulphate and zinc sulphide), barytes and red lead are used. Green earth is mostly used for lime colours for colour-washing walls. The finest and most transparent pigments such as are required for artist's colours and printing inks are made with alumina alone or with Blanc Fixe. Example. 20 parts aluminium sulphate (2½% solution), 10 parts soda ash (Na2CO3, 10% solution), 5-10 parts acid or direct cotton dyestuff (2% solution), 10-100 parts barytes, 30-50 parts barium chloride (10% solution). For a finer lake, barytes would be omitted or replaced by Blanc Fixe in small amount.
A few natural colouring matters also serve for lake production. The chrome and iron compounds with logwood give deep blue-black and brownish-black lakes. Brownish lakes are similarly obtained from quercitron and fustic, and red and maroon lakes from the red-woods, using alum, tin, chrome, etc.
The use of dyestuffs for colouring foodstuffs, wines, etc. is extensive and some care is demanded in their selection as many dyes possess more or less pronounced toxic properties. In general the following types are unsuitable: strongly basic dyes, nitro dyestuffs, dyes marketed as metallic salts of a harmful nature, e.g., zinc salts, or as double compounds with poisonous bodies, e.g., double oxalates like Malachite Green, dyes contaminated or liable to contain traces of poisonous bodies, e.g., arsenic used in Magenta manufacture which may be left in traces in the finished product.
The following well-known artificial dyestuffs are allowed by the United States Government for colouringfoodstuffs: Naphthol Yellow S, Orange I, Amaranth, Ponceau 3R, Erythrosine, Light Green SF yellowish, Indigo Disulphonate.
Other well-known dyestuffs suitable are Acid Magenta (R.H.), Auramine, Benzopurpurine, Metanil Yellow, Titan Scarlet (R.H.).
Natural dyestuffs are usually preferred for colouring foodstuffs wherever applicable, and cochineal, turmeric, annatto, and Persian berries are largely used. Tincture of Cochineal is an aqueous-alcoholic extract of cochineal. The dried petals of safflower are used as a cosmetic.
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Additional information may be acquired from the handbooks on dyeing in the Cambridge Technical Series. Reference may also be made to Jennison's Lake Pigments from Artificial Colours, Berach's Mineral and Lake Pigments. Also the sections of Thorpe's Dictionary of Applied Chemistry (1912) on Dyeing, Lakes, Inks etc., and papers in the Journal of the Society of Dyers and Colourists. The literature issued by the various dyestuff' manufacturers is replete with information on every branch of dyeing.
Note on Prices. The prices at which dyestuffs are sold are variable and precise information is often difficult to acquire. The following short list of approximate prices in 1914 before the war will be of service to students possessing no inside knowledge of the trade: Aniline 5d.-5½d. lb., carbolic acid (cryst.) 39°-40°C. 3½d.-5d. lb., picric acid (cryst.) 11d. lb., p-nitraniline 8d. lb., beta-naphthol 5 5/8d. lb., phenylene diamine 1s. lb., resorcin 1s. 7d. lb.
Basic Dyestuffs. Auramine 1s.-2s. lb., Bismarck Brown 10d. lb., Chrysoidine 10d. lb., Malachite Green 1s. 6d. - 1s. 9d. lb., Magenta 2s.-2s. 3d. lb.; Methylene Blue 2s.-2s. 6d. lb., Rhodamine 1s. 6d.-2s. lb.
Acid Dyestuffs. Acid Violets, Acid Blues and Blacks 1s.-1s. 6d. lb., Oranges 5d.-1s. lb., Orange II 5d. lb., Ponceau 1s. lb., Scarlets 5d. (and upwards) lb., Crocein Scarlet 1s. 6d.-2s. lb., Victoria Scarlet 2s. 6d.-3s. lb., Tartnizine Pure 9d.-1s. 3d. lb., Naphthol Yellows 6¾d. lb., Fast Red A 7d. lb., Fast Red Extra 1s. 4d.-1s. 9d. lb., Soluble Blues 10d-ls. 1d. lb., Brilliant Milling Green type 1s. lb., Patent Blue type 1s. 6d. lb., Indigo Extract 3d.-5d., Refined 4d.-l0d. lb.
Direct Cotton Dyestuffs. Benzopurpurines 6d.-9d. lb., Chrysophenine 9d. (and upwards) lb., Diamine Black RO, BH ami developing blacks 1s. 6d.-ls. 10d. lb., Direct Blacks 1s.-1s. 6d. lb., Diamine Sky Blue and similar dyestuffs lld. lb., Direct Pinks, Oranges, Greens, Reds and Violets 1s.-2s. 6d. lb., Yellows and Browns 7d.-1s. 2d. lb.
Mordant Dyestuffs. Alizarin 4½d. lb. (20% paste), Alizarin Red (20%) 5½d. lb., Bluish Shade 6d.-7d. ld., Chrome Blues 1s. 4d.-1s. 6d. lb., Gallein (20%) 6½d.-7d. lb., Diamond Black type 7½d. lb., Acid Alizarin Blues 6s.-9s. lb.
Sulphur Dyes. Blacks 6d.-11d. lb., Browns 6d.-1s. lb., Blues 1s.-1s. 3d. lb., Greens 1s.-1s. 6d. lb., Yellows 6d.-8d. lb.
Vat Dyes. Indigo (20 % paste) 8d. lb.
Natural Dyestuffs. Indigo, Bengal 2s. 10d.-5s., Oude 2s. 6d.-4s., Kurpah 1s. 9d.-3s. 4d. lb., Logwood £6-£7½ ton, Logwood Extract and Haematein Paste 20s.-30s. cwt., Haematein Crystals 50s.-65s. cwt., Barwood £7¼ ton, Camwood £16 ton, Peach wood £10 ton, Cochineal 2s.-2s. 6d. lb., Cudbear 4d.-5d, lb., Orchil Extract 25s.-30s. cwt., Persian Berries Extract 36s. cwt., Flavin 1s. 6d.-2s. 9d. lb., Fustic £5½ ton, Turmeric (Bengal) £21 - (Madras) £26 ton, Annatto 6d.-1s. 6d. lb., ditch and Gambler 20s.-36s. cwt.
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