Page:1902 Encyclopædia Britannica - Volume 27 - CHI-ELD.pdf/614

 562

DYE I N G

In co<fo?i-dyeing the above colouring matters are chiefly used for the production of so-called Turkey-red, a colour remarkable for its brilliancy and its fastness to light and soap. These properties are due to the preparation of the cotton with oil, in addition to the ordinary mordanting and dyeing, whereby there is fixed on the fibre a permanent and stable lake, in which aluminium and calcium are combined with Alizarin and some form of oxy-fatty acid. In the older processes employed, the preparation of the cotton with oil was effected by passing the material several times through emulsions of olive-oil and potassium carbonate solution ; at a later date, and even now in the case of cloth, the cotton is first impregnated with hot oil (Steiner’s process), then passed through solutions of alkali carbonate. After the preparation with oil or oil-emulsions, the cotton is “ stoved,” i.e., heated for several hours in special chambers or stoves to a temperature of about 70° C., during which operation the oil is decomposed and oxidized and becomes indelibly attached to the fibre. The oil-prepared cotton is steeped in cold solutions of basic aluminium sulphate or acetate, washed, dyed with Alizarin, and finally boiled for several hours with soap solution under pressure in order to brighten the colour. In the more recent and much more expeditious “ sulphated-oil process,” castor-oil is employed instead of olive-oil, and before use it is submitted to a treatment with sulphuric acid, the sulphated oil thus obtained being finally more or less neutralized with alkali. The cotton is impregnated with this sulphated-oil solution, dried, mordanted with aluminium acetate, dyed, dried, steamed, and soaped. The operation of steaming plays an important part in brightening and fixing the colour-lake on the fibre. In these and all other Turkey-red processes, the oil, probably in the form of an oxy-fatty acid, acts as a fixing agent for the aluminium and enters into the composition of the red lake, imparting to it both brilliancy and permanency. Alizarin S is a sulphonic acid derivative of Alizarin, and since it is much more soluble, it, readily yields level colours. Silk is dyed in a similar manner to wool, the fibre being mordanted by the ordinary methods and then dyed in a separate bath. Diamine Fast Red is applied to cotton as a Direct Colour, with the addition of soda or soap to the dyebath. By treating the dyed colour with a solution of fluoride of chromium, its fastness to washing is materially increased. Wool is dyed in a similar manner, sodium sulphate being added to the dyebath, and the dyed colour treated with fluoride of chromium or bichromate of potash. The colour is so extremely fast to light and to milling on wool that it may well serve as a substitute for Alizarin. Alizarin Orange is employed in the same manner as Alizarin. In wool-dyeing it is usually applied on chromium mordant for browns and a variety of compound shades in combination with other Alizarin Colours and dye wood extracts, less frequently on aluminium mordant. Galloelavin is used in wool and silk dyeing on chromium mordant as a substitute for Fustic and other yellow dye woods, to furnish the yellow part of compound shades. The Alizarin Yellows, R and GG, Anthracene Yellow, Diamond Flavine, Chrome Yellow, Diamond Yellow, Carbazol Yellow, Chrysamine, &c., are Direct Colours with mordant-dyeing properties. They also serve as substitutes for Fustic in wool or silk dyeing, and are dyed either on a chromium mordant, or first in an acid bath and afterwards saddened with bichromate of potash. Cceritlein is employed in dyeing wool, silk, or cotton with aluminium or chromium mordants, either as a self-colour or for compound shades. With aluminium mordant the colour is a moderately bright green, more particularly on silk; with chromium mordant, an olive-green. Ccerulein S is the more soluble bisulphite compound of the ordinary Coerulein. It is applied in the same manner, care being taken, however, to dye for some time (one hour) at a temperature not exceeding 60° C. until the bath is nearly exhausted, and then only raising the temperature to the boiling-point. Without this precaution Coerule'in S is decomposed, and the ordinary insoluble Ccerulem is precipitated. The colours obtained are very fast to light. Fast Green, Dioxine, and Gambine are chiefly of use in calico-printing and in wool-dyeing. With iron mordant they yield olive-greens, which on wool are extremely fast to light. Cotton is impregnated with ferrous acetate, dried, aged, and fixed with silicate of soda, then dyed in a neutral bath. Wool is mordanted with ferrous sulphate and tartar (3 per cent, of each) and dyed in it neutral bath. Acid Alizarin Green, Alizarin Cyanine Green, and Diamond Green, all dye wool direct in a bath acidified with acetic or sulphuric acid, and the dyed colour may be afterwards fixed or saddened with bichromate of potash, or they may be dyed on chromium-mordanted wool. The first method is very useful for pale shades, since the colours are very level or regular. Alizarin Blue is a dark blue dyestuff which, owing to the fastness of the colours it yields, has for many years been regarded as a worthy substitute for Indigo in wool-dyeing. It is applied in the same manner as Alizarin, the chromium mordant being alone

employed. Alizarin Blue S is the soluble sodium bisulphite compound of Alizarin Blue ; it corresponds, therefore, to the abovementioned Cterulein S, and in its application the same precautions as to the temperature of the dyebath are necessary. The fastness of the dyed colours to light, milling, and acid satisfy the highest requirements. Alizarin Cyanine, Anthracene Blue, and Brilliant Alizarin Blue were discovered later than the above-mentioned Alizarin Blues, and, owing to their greater solubility and other advantages, they have largely replaced them as substitutes for Indigo. They are dyed on chromium-mordanted wool, silk, or cotton, and yield dark purplish or greenish blues, according to the particular brand employed. The fastness of the dyed colours to light, and general durability, are very satisfactory, but in fastness to milling and acids they are to some extent inferior to Alizarin Blue. Celestine Blue and Chrome Blue dye purplish blue and bright blue respectively, and are dyed in the ordinary way upon a chromium mordant. The colours they yield are inferior to the Alizarin Colours in fastness to light, but on account of their clear shades they are often used for brightening other colours. Brilliant Alizarin Cyanine and Alizarin Saphirole are true Alizarin Colours, and possess the same fastness to light as other colours of this class. Unlike most of the Alizarin Colours, they are capable of dyeing wool satisfactorily without the aid of a metallic mordant—namely, with the addition of sulphuric acid to the dyebath, in the same manner as the Acid Colours. If necessary, the dyed colours may be treated with bichromate of potash. The colours thus produced are very fast to light and very level, hence these dyestuffs are valuable in the production of the most delicate compound shades, such as drabs, slates, greys, &c., which are desired to be fast to light. Alizarin Saphirole dyes clear blue, the colour produced being much more brilliant even than those of Brilliant Alizarin Cyanine. Gallein, Gallocyanine, and especially Chrome Violet, dye somewhat bright purple shades, and are hence frequently employed for brightening other colours, but they are only moderately fast to light. They are applied in the usual manner on a chromium mordant. Anthracene Brown is largely employed in the production of compound shades. It dyes a dark, somewhat reddish, brown on chromium mordant, the colour being very even and extremely fast to light. Chromogen is a greyish white powder, readily soluble in water, with a pale brown colour. It is attracted and absorbed by wool in a boiling acid bath ; at this stage the wool remains colourless, but by subsequently boiling it with a little bichromate of potash in the same or in a separate bath the absorbed chromogen is oxidized and the brown colour is developed. Alizarin Black is dyed on chromium mordant in the same manner as Alizarin, and is used as a self-colour or in combination with other Alizarin Colours. Diamond Black and the following three colours mentioned in the list are very useful for dyeing good blacks on wool, fast to light and acids. The wool is first dyed with the addition of acetic and finally sulphuric acid. When the dyebath is exhausted, bichromate of potash (2 per cent.) is added, and boiling is continued for half an hour longer. Chromotrope, of which there are several brands, is an Acid Colour which is applied to wool in an acid bath in the usual manner. The red or purple colours thus obtained are saddened in the same bath with bichromate of potash and changed into black, the colouring matter being oxidized and simultaneously combined with chromium. Miscellaneous Colours.—Under this head there may be arranged a few dyestuffs which, although capable of inclusion under one or other of the foregoing groups, it is more convenient to treat of separately. Indigo, Aniline Black, and Catechu, for example, might be placed in the class of Developed Colours, since they are all developed on the fibre, and indeed by the same method—namely, by oxidation. Indigo is one of our most important blue dyestuffs, which has been employed from the earliest times. It may be obtained from various plants, the chief of which are the European woadplant Isatis tinctoria, the Chinese and Japanese indigo-plant Polyqo7ium tinctorium, and the indigo-plant of India, Indigofera tinctoria, &c., but the chief supply is obtained from the lastmentioned plant, which is largely cultivated in India. Curiously enough, the living plant contains no indigo, but an indigo-yielding substance called indican, which is converted into indigo during the process of extraction by the joint influence of fermentation and oxidation, there being simultaneously separated a sugar product called Indiglucine. In India the fresh plants are steeped in large tanks containing water ; fermentation soon begins, and lasts for about fifteen hours, when it subsides ; at this stage a clear yellow liquor is drawn off into shallow tanks, and there agitated in contact with the air, whereby the indigo is produced and precipitated as