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.
On account of its cost and little durability carthamine red is not used in painting. It is principally employed in the artificial flower industry for colouring flowers. Pure carthamine or a mixture with finely powdered steatite is applied by rubbing.
Alkanet.—The roots of alkanet (Alkanna tinctoria) contain in the bark a fine red colouring matter, from which also a violet lake can be obtained, though this is rarely made. The plant is largely grown in Southern Europe and also around Vienna. The colouring matter is obtained pure by macerating the root for a long time with water and then treating with strong alcohol, which dissolves the colouring matter, together with a large quantity of resin. The alcohol is distilled off, the residue extracted with ether, and the ethereal extract treated with a large quantity of water, which extracts the colouring matter. This is left in the pure state, when the solution is slowly evaporated.
According to Carnelutti and R. Nasini alkannin is obtained by extracting the root of Anchusa tinctoria with petroleum ether, evaporating, treating the residue with weak caustic potash, filtering, and shaking the filtrate several times with ether. The solvent is removed, the colouring matter precipitated by carbonic acid, dried over sulphuric acid, and dissolved in ether. The filtered solution is then allowed to evaporate. Alkannin is then obtained as a dark brownish-red mass, which is easily powdered. It has a metallic lustre, and readily dissolves in alcohol, glacial acetic acid and chloroform.
When alum is added to the aqueous solution of the colouring matter a beautiful violet precipitate separates, which when dry is very suitable for artistic purposes. Alkanet is little used. It is completely replaced by much cheaper colouring matters.