When lac dye is treated with hydrochloric acid the colouring matter dissolves; the solution can be used to dye wool, which it colours a beautiful red. The colouring matter is very similar in appearance to that of cochineal, but has the appearance of much greater fastness. It appears also to be similar in composition to carminic acid, but little is known as to its chemical constitution.
When lac dye is to be used for painting it must be freed from resin; this is accomplished by treating the finely powdered mass for a long time with boiling alcohol and separating the solution of resin from the undissolved colouring matter, which is then dried. In this way a lake is produced known commercially as Vienna red and little inferior to carmine lake. Unfortunately the price of lac dye, although it is imported in large quantities from India to England, is so high that it can only be used for artists’ colours.
CHAPTER LIII.
SAFFLOWER OR CARTHAMINE RED.
The safflower or bastard saffron (Carthamus tinctoria) grows wild in Southern Europe, and is also cultivated. It contains two colouring matters, yellow and red. The former is not used in dyeing, but is employed for colouring liqueurs, since it is innocuous. The red colouring matter is used for colouring artificial flowers and for fine cosmetics; formerly it was employed in dyeing, but is now rarely used for this purpose, since carthamine red has little permanence and can be replaced by cheaper dyes.
The yellow colouring matter, which is not used, is generally removed by treating the corolla of the safflower, which contains the colouring matter, with water. After this treatment it is known as washed safflower. In the dried corolla of the flower up to 36 per cent. of the yellow colouring matter is found, whilst only 0·4 to 0·6 per cent. of the red is contained.
It appears that the colouring matter of the safflower has been used from the most ancient times. The Chinese employ it to obtain a handsome cosmetic, the Tyrians are said to have used it in dyeing. In Europe it was not cultivated before the seventeenth century, when it came into use for dyeing.
In order to obtain pure carthamine red—and this is the form in which it is generally used—safflower is treated for a long time with water containing a little acetic acid until a yellow solution no longer results. The residue is then treated with soda solution for several hours, when the colouring matter dissolves; the solution is filtered and neutralised with acetic acid. Cotton is then introduced. Carthamine red is a colouring matter which at once dyes animal and vegetable fibres when these are brought in contact with its solution. Thus the whole of the colouring matter is precipitated on the cotton, which is coloured a deep red. After twenty-four hours the cotton is taken out, washed, and treated with soda solution, in which the colouring matter dissolves. When this solution is carefully neutralised with citric acid the colouring matter separates in the form of fine flocks. These are collected, dissolved in strong alcohol, the solution evaporated to a small volume, the colouring matter again precipitated by the addition of a large quantity of water, and washed with pure water until the wash waters begin to be coloured red. The pure carthamine thus obtained is spread upon small cups, in which it dries to a beautiful red mass which in somewhat thicker layers has a fine green lustre. It is brought into commerce as ”cup red” or ”plate red”.
The small quantity of colouring matter contained in the safflower, as well as the complicated process for obtaining it, make it evident that this colouring matter will be among the most expensive found in commerce. The high price is, however, neutralised by its great colouring power, and by the fact that nothing can in all cases replace it for colouring the best artificial flowers.
Safflower Carmine.—This substance, used by dyers, is a solution of carthamine red in soda solution. It is only necessary to add an acid after once introducing the fabric in order to fix the colouring matter at once upon the fibre.
The shades produced by carthamine red are distinguished by a delicacy of tint not produced by other dyes; all shades between the deepest red and the palest rose-red may be obtained from it. Unfortunately it is very susceptible to the action of alkalis; one careless washing of an article dyed with carthamine is sufficient to remove the greater part of the colour.