The madder lakes are equally as permanent as the madder colouring matters dyed upon fabrics. On this account and because of their handsome colour they are highly prized by painters. The best qualities of madder are necessary to produce fine lakes; it is more convenient to use garancin or madder extract. Only when the colouring matter is tolerably free from the foreign substances which accompany it can a pure red madder lake be produced; the poorer qualities of madder produce a lake which is not a pure red and is never bright. The good repute of the madder lakes of certain makers is in great part due to careful choice of the raw materials. This choice and care in the process are the secrets of the manufacturers who produce good madder lakes.

The author has found that the finest lakes can be obtained without difficulty from the alizarin, separated in the before-mentioned manner from madder by means of sulphuric acid. The small cost of obtaining crude alizarin by this process enables it to be used on a commercial scale. The labour involved in the process is far outweighed by the excellent qualities of the lakes produced.

A very bright lake is obtained directly from madder by treating with sulphuric acid (thus garancin is really used), digesting the mass for several hours with a solution of alum absolutely free from iron, filtering and adding at first a small quantity of soda solution; a little madder lake is precipitated which is of the finest shade. When this lake has settled the liquid is poured off and again mixed with a little soda solution. The lake now precipitated is inferior to the first, if the madder is not of specially fine quality. By this fractional precipitation of the colouring matter, madder lakes varying in beauty are produced; the separate fractions often differ considerably in shade, this is because the later portions are more and more contaminated by the foreign substances contained in the madder.

From inferior madder lake, which could only be sold at a low price, a lake of the best quality can be produced in the following manner: The lake is finely powdered, mixed with acetic acid and left to stand twenty-four hours; the madder lake dissolves in the acid to a fine red solution, whilst the impurities remain on the filter when the solution is filtered. The clear solution is mixed with a large volume of water free from lime, and the acetic acid neutralised by soda, when pure madder lake separates. The addition of soda is not continued until all the lake is precipitated, but only until the liquid is still slightly red. Hydrochloric acid may be used instead of acetic; it is much cheaper, but must be absolutely free from iron.

It has already been stated that the crude alizarin prepared as described above is well suited as a source of madder lake, since it is free from the majority of the substances which injure the purity of the shade. It is treated with a boiling solution of alum and filtered whilst hot; madder lake is then precipitated by cautious additions of soda, the first portions precipitated being the best.

Madder Carmine is not often found in commerce; it consists of the almost pure lakes of alizarin and purpurin. The process by which this valuable pigment is produced is based upon the great stability of the madder colouring matters. The following is the process on the large scale: Good madder, very finely ground, is spread out in small heaps in a room, the temperature of which is about 16° to 18° C.; the heaps are moistened with water and left for several days. The mass ferments and gives off a peculiar smell; in the fermentation not only is the glucoside decomposed, but also many of the other compounds contained in the madder, consequently the mass becomes dark and considerably diminishes in weight. The end of the fermentation process may be recognised by a little practice with tolerable certainty by the disappearance of the peculiar smell; the mass is broken up and transferred to a lead-lined vessel, in which it is mixed with three or four times its weight of ordinary sulphuric acid. The acid is allowed to act for several hours, the plant fibres are almost completely charred, and the mixture becomes black. When the charred residue has settled, the liquid is filtered through pure quartz sand or powdered glass, and mixed with a large quantity of water. The carmine, which is insoluble in water, separates as a red powder; it is then washed and dried.

The colour of madder carmine is of such beauty that it can only be compared with that of good cochineal carmine, but it is incomparably more permanent than the latter and may be used in all varieties of painting.