The best artificial alizarin of commerce occurs as a yellowish powder, presenting the aspect of raw sienna. It may, however, be obtained in yellow or orange red crystals, either by repeated crystallization from a solvent or by sublimation in vacuo. Its colour is always brighter than that of purpurin, which in powder has about the hue of Venetian red. But when solutions are made of these two substances in alkalies, then it is seen that the colours are reversed - alizarin yielding a crimson verging upon purple, and purpurin a red verging upon crimson. Differences of colour will be noticed in the lakes prepared with these two bodies. The directions for preparing pigments from the above-named bodies are practically identical with those already given in outline, but the minute details of manipulation can be learned only in actual practice. The following process gives an artificial red madder of excellent hue: Equal weights of pure alum (absolutely free from iron and lime) and of the purest artificial purpurin in powder are ground together, and then washed with cold water until the washings are colourless; then the residue on the filter is boiled with a 5 per cent. solution of pure alum, filtered while boiling, and immediately neutralized with pure sodium carbonate solution (also boiling) until red flocks appear.

These are filtered off, and constitute, when washed and dried, a fine pigment of a rich red hue. By heating the mother liquor to 80°, and adding more sodium carbonate, a further and equally good product is obtained. The purpurin residue, when again heated with more alum-solution and precipitated as above directed, yields a further quantity. The final residue, after several such exhaustions, produces an impure lake, having a brownish-red hue. A very large number of commercial preparations of alizarin and of other dye-stuffs closely allied to it are now available for the preparation of the so-called 'madder lakes.' Some of these preparations when dissolved and then precipitated on a suitable basis, yield pigments of great richness and stability, others, especially those which possess a yellow, orange, or red-brown hue, are less permanent. Here it may be remarked that, broadly speaking, the true or 'root' madders are complex so far as their colour-constituents are concerned and simple as regards their base, while the converse is true of the alizarin lakes.

Although the madder colours are very much less affected by light than are the pigments derived from cochineal, yet it cannot be affirmed that any of them are absolutely permanent when continuously exposed. The following figures show approximately the amount and nature of the change, observed after certain intervals, in the case of several madder pigments used as water-colours:

The letters A to F indicate different samples of the several pigments, which were in all cases 'moist' colours; a parallel but less complete series with 'cake' colours gave practically the same results. The five samples marked* are instances of exceptional stability, and are of importance as showing the possibility of obtaining some, at all events, of the madder pigments in a satisfactory form. It is noticeable that the paler (pink and rose) madders, which contain much water, are generally more perishable than the concentrated madder carmine; the comparative trials having, of course, been made with washes of nearly the same depth of tint.

A study of this table inclines one to think that the genuineness and purity of some of these pigments are doubtful, yet one specimen only (Madder Carmine C) was not tested. In this case the material used was not available for analysis, but I have no reason to doubt its authenticity.