The Chemistry of Dyestuff. Dyestuffs. XXVI. Natural Dyestuffs.

A Manual for Students of Chemistry and Dyeing
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)


1 Flavone itself occurs almost pure as the mealy deposit found on the leaves of many plants of the primula class.
Most natural dyestuffs are mordant dyestuffs and occur as glucosides in plants. Among these, the yellow dyestuffs which have been identified are mainly oxyderivatives of flavone1 or flavanol.

Young Fustic contains a tri-oxy-flavanol termed [-] Fisetin. It is obtained from the wood of the sumach tree (rhus cotinus), a small tree indigenous to Southern Europe and the West Indian Islands. It is polygenetic and may be applied to the dyeing of wool. On account of the shades obtained from it lacking permanency it is little used.

Old Fustic is the wood of the tree chlorophora tinctoria, previously termed morus tinctoria. It is principally used in the dyeing of wool. Fustic consists mainly of two dyestuffs: Morin and Maclurin.

These are polygenetic, giving yellow shades with aluminium, tin and chrome, and olive with iron and copper mordants, although morin does not contain ortho-oxy-groups "(see p. 110).

The wood of the Osage Orange tree found in the United States behaves like Fustic in dyeing.

Patent Fustin is a colouring matter placed on the market which is mainly disazobenzene maclurin. It is obtained by extracting Old Fustic with boiling water, the solution filtered from the morin and its calcium salt, which separate on cooling, the filtrate neutralised with sodium carbonate and diazobenzene sulphate added until no further precipitation takes place; this precipitate is collected, washed, and sold in paste form. The disazobenzene maclurin has the following formula:[-]

Persian Berries consists of the dried unripe fruit of various species of rhamnus. It consists mainly of two flavanol derivatives, rhamnetin and rhamnazin, and small quantities of quercetin. It is employed for dyeing paper, leather, wool, in wool and calico printing for yellow shades, and for colouring foodstuffs.

Turmeric is contained in the tuber of curcuma tinctoria. It is now mainly employed for tinting and flavouring butter, cheese, confectionery, and for tinting lakes, fats and varnishes.

It is interesting as it is directly absorbed by cotton, and may be dyed in presence of a little acetic acid or alum. It is feeble to light and alkalis, acquiring a brownish red tint by treatment with the latter.

Annatto is obtained from the fleshy pulp surrounding the seeds of bixa orellana. It is mainly cultivated in Central America, in Cayenne, in Brazil, and in India, the latter giving the best seeds. The colouring matter is termed bixin C28H34O5. Owing to the fugitive nature of the red and orange shades obtained by it, its employment is very limited.

It is used for colouring butter, cheese, margarine, soups, etc.

Quercitron Bark is the inner bark of a species of oak, quercus discolor; it is indigenous to the Central and Southern States of America. The epidermis or outer blackish bark is shaved off and the inner portion detached and ground or extracted. Although a very useful natural colouring matter, it has been considerably replaced by the cheaper Old Fustic. The colouring matter of quercitron consists of a tetraoxy flavanol termed quercetin.
It is a polygenetic dyestuff, giving shades very similar to fisetin.

The dyestuff is present in the bark partly as a glucoside, quercitrin. The glucoside quercitrin, like the dyestuff quercetin, is also polygenetic.

Flavin is a commercial preparation of quercitron bark. It is obtained by extracting the bark with water at 103°C. Two brands are known: yellow flavin, which consists mainly of quercitrin, and red flavin, which is mainly quercetin. The red flavin is obtained by ammoniacal extraction of the bark.

Patent Bark is obtained by boiling quercitron bark in powder with three times its weight of 5% sulphuric acid for about two hours; it is then filtered, washed and dried.

The preparations from quercitron bark are more powerfully tinctorial than the bark itself.

Weld consists of the plant reseda luteola; it contains mainly a textra-oxy-flavone luteolin.

It is polygenetic, and is employed to a small degree for the dyeing of all fibres, but mainly silk.

Dyer's Broom (Dyer's greenweed) is found in Central and Southern Europe, in Russian Asia, and is frequent in the greater part of England. It contains a flavone luteolin, the dyestuff of weld, and a cumarone genistein, a feeble polygenetic dyestuff, which has the following constitution:

The yellows obtained from Fustic, Quercitron Bark and Weld are similar in their application and fastness. In the latter respect they are good, but not equal to the best acid dyes as regards light-fastness. Nevertheless, Fustic and preparations of Quercitron Bark were largely used even before the European War occasioned a shortage of the competing artificial products.

Indian Yellow (Piuri) is obtained by heating fresh urine of cows fed upon mango leaves. The yellow mass that separates is pressed in cloths and is then rolled into balls. In this form it is the magnesium salt of euxanthinic acid [-] which on hydrolysis gives euxanthone [-]
It is mainly employed for colouring oil and water paints.

Cochineal consists of the dried insect coccus cacti, largely cultivated in Mexico. Carminic acid, the colouring matter of cochineal, probably has the empirical formula C22H22O13. It crystallises from water or alcohol in red prisms; it darkens without melting at 130°C., and yields with alcoholic potash a monoand a dipotassium salt. On distillation with zinc dust naphthalene is obtained. It was formerly much used on a tin mordant for the scarlet or "grain" dyeing of wool and silk, but its use is now declining, as although fast to light it cannot compete with acid scarlets in other respects. It is used also as a tint for microscopic work, and for the colouring of foodstuffs, etc.

Lac Dye is produced by an insect coccits lacca or ficus. Stick lac used for dyeing is deep red or brown and contains about 70 per cent, of resin and 10 per cent, of dye. The lac dye is obtained by extracting the stick lac with soda carbonate solution, evaporating the extract and moulding the concentrated extract into cakes. For dyeing purposes the lac dye is treated with dilute hydrochloric acid to remove mineral matter. It is poly gene tic and is similar to cochineal, giving shades of good fastness to light but turned bluish by milling. Although faster to light than cochineal it has almost entirely gone out of use, while cochineal has remained in fairly extensive application. The main reason lor this is the greater insolubility of lac dye, which can only be overcome by more laborious preparation for dyeing, e.g., grinding with hydrochloric or oxalic acid.

Archil, Orchil and Cudbear are prepared from certain lichens, roccella tinctoria, lecanora tartarea etc., by submitting them to the action of oxygen (air) in presence of ammonia, or the plant is boiled with lime and water, allowed to settle, ammonia added and exposed to the air until dyestuff no longer separates. Archil appears in commerce as a pasty mass, and a reddish powder, cudbear.

The dyestuff can be obtained from Orcin by the rapid action of hydrogen peroxide and ammonia, or slowly by the action of air and ammonia. The products vary according to the time of action of the reagents.

The colouring matter (orceïn) dyes best from a neutral bath, but it may be dyed from slightly acid or alkaline baths. It is used for the dyeing of crimson on wool and silk, with or without mordants. The dye is largely used in conjunction with indigo for the dyeing of wool, being used both as a bottoming and as a topping colour. Although rather fugitive according to modern standards, it is still used for crimson in silk dyeing.

Catechu or cutch is a valuable dyestuff obtained from the dark red heart wood of Acacia, Areca, and Uncaria, growing in India. It is largely used for obtaining various shades of brown, olive, drab, grey, and black, and is employed for dyeing both animal and vegetable fibres.

In practice catechu is now seldom used, as a product "prepared cutch," which is obtained by heating catechu with aluminium sulphate, possesses greater colouring power.

Cutch is remarkable for the brown colour produced on cotton by chroming, the colour being very last to light, soap, alkali, acid, and also to bleaching liquor. Its use on wool is restricted owing to rendering the fibre harsh, but large quantities are used as a mordant in dyeing blacks on silk.

Catechin, one of the substances present in catechu, has the following constitution: [-]

Gambler catechu (or "Gambier"), in addition to catechin, contains a small amount of catechutannic acid, this substance being present in large quantities in the deep brown varieties of cutch. Catechutannic acid is said to be produced when catechin is heated to 110°C. It is a powerful tanning agent. Catechin is not precipitated by gelatin, and is not itself a tannin matter; it is, however, absorbed by hide, and there gradually passes into catechutannic acid.

Soluble Red Woods. - Brazil Wood, Peach Wood, Sapan Wood, and Lime Wood. These dyewoods are obtained from various species of caesalpinia. They have similar dyeing properties, and on account of the fugitive character of the colours they yield they are only used to a limited extent.

The woods contain the leuco dyestuff brasilin.

This oxidises in aqueous solution by exposure to air to the dyestuff Brasileïn.

Insoluble Red Woods. - Camwood, Barwood, and Sanderswood or Sandal Wood. The wood contains the dyestuff termed santalin, present to about 17% in sanderswood and 23% in barwood. These dye woods are obtained from certain species of pterocarpus and baphia.

They are principally used in wood-dyeing, in conjunction with other dyestuffs. Jn some combinations, e.g., with logwood, their inferior fastness does not reveal itself as might be imagined from separate tests. The dyestuff is polygenetic.

Logwood or Campeachywood consists of the heart wood of haematoxylon campechianum growing chiefly in Central America, Mexico, etc. The best sorts come from Mexico, Haiti, San Domingo, Honduras, Cuba, Jamaica, and Guadeloupe. There is also on the market an extract of the wood of variable strength. The principal use of logwood is for the production of blacks upon both animal and vegetable fibres, and it is often used for this purpose along with Fustic. It is a polygenetic dyestuff and gives, with an aluminium mordant, a blue colour; chrome, blue-black; iron, black; copper, green-black; and tin, violet.

The wood contains the leuco compound haematoxylin, and is therefore similar in constitution to brasilin.

By oxidation of haematoxylin, generally in ammoniacal solution by exposure to the air, haemateïn is produced, which probably has the following constitution:

Haeinateïn is converted into a colourless body by sulphurous acid or sodium bisulphite solution, readily soluble in water. No reduction, however, appears to occur, as on addition of an acid or on boiling, haematem is precipitated; also with zinc and acid, with stannous chloride and caustic soda, the solution is decolourised, but on standing the solution is again restored to its former tint.

Logwood used to be "aged." This process consists in piling the "chips" or "rasps" in a moist condition in a large airy chamber. The mass oxidises and the yellow wood turns dark reddish brown. At the present time this method is seldom used, as formerly iron was chiefly used as mordant, whereas bichromate is the mordant mainly used now for blacks, and the yellow chrome mordant oxidises the haematoxylin to haemateïn.

Logwood extract is still oxidised to obtain haemateïn, the oxidation being mainly done by means of sodium nitrite.

Commercial haemateïn crystals are among the best forms of logwood extract, and are usually much stronger in colouring power than solid logwood extract.

Woad is a dark clay-like product made from the leaves of the woad plant, isatis tinctoria. The plant is a biennial, indigenous to Europe, and has long been used for dyeing blue. The ancient Britons stained their skin blue with woad in time of war and in connection with certain religious observances. It was largely cultivated before the introduction of indigo from India. Woad is still grown in Lincolnshire and Huntingdon. The leaves are subjected to a fermentation process to prepare it for the market. Woad, although previously used for dyeing blue, is now only employed as a fermenting agent in the indigo-vat as used by the wooldyer. The vat so prepared is therefore termed the "woad-vat." Woad was considered to contain the same colouring matter as is present in the indigoferae. It is now known to be a distinct substance, which in most of its reactions resembles indoxylic acid.

(The student seeking further information on natural dyestuffs is recommended to consult the various articles by A. G. Perkin in Thorpe's Dictionary qf Applied Chemistry, also Die natürlichen Farbstoffe, Rupe.) The slight commercial importance of natural dyes as a class does not warrant further space being assigned to them in this book. All those dealt with above are still more or less in actual use, but only logwood, indigo, cutch and fustic are now of considerable importance in normal times. The famine in synthetic dyestuffs experienced by most nations except Germany during the European war, caused a transient revival of interest in the use of natural products for dyeing. This, however, is not likely to be repeated, as in most cases steps have been taken to prevent any future recurrence of shortage from the same cause.

Ei kommentteja :