To obtain the best lake from fustic the alum used must be completely free from iron, otherwise only a dirty green lake is produced. Since the least trace of iron damages the shade of the colour, fustic lake is more frequently made by means of lead oxide. To obtain the lead fustic lake the decoction is allowed to stand for several days, so that the morin, which together with maclurin forms the colouring principle of fustic, may separate; the liquid is filtered from the precipitate, and lead acetate solution added which has been boiled with litharge to saturation, so that the most basic acetate is produced. The lead fustic lake has a deep yellow colour; it is well adapted for use in painting, but, like all lead pigments, is not specially permanent in air. By admixtures of levigated chalk or starch paler shades of the dull yellow lake are obtained. =Quercitron Lake.=—Lakes are seldom made from quercitron alone, although they possess a deep yellow colour; they are more frequently employed in dyeing when they are produced directly upon the fibre. Quercitron lake can be made by treating the aqueous decoction of the ground bark with tin crystals and a little alum solution. With tin crystals alone a darker yellow lake is obtained than when alum is used at the same time. Different shades may thus be produced. Extract of quercitron bark comes into commerce as a greyish yellow powder under the name of flavine, which has great colouring power, and may be used with advantage in the place of aqueous extracts of the bark. Since the discovery of the aniline dyes the applications of all lakes have been largely extended, since the dyes enable brighter shades to be obtained without the many processes necessary when natural colouring matters are used, and do not require so much skill on the part of the workman. This applies not only to yellow colouring matters, but to the many other colouring matters formerly used by the dyer. The principal reasons which have so quickly brought the new dyes to the front lie in their greater beauty and in the diminished labour required in their use. =Purree or Indian Yellow= must not be confounded with the yellow cobalt pigment known also under the latter name. It is a compound of magnesia with an organic acid—euxanthic acid. It is obtained from the urine of cows fed upon mango leaves. It comes into commerce in lumps weighing about 50 to 60 grammes, which are dark brown on the exterior, but on fracture show a fine orange yellow colour. Indian yellow is little used, and is not likely to attain importance. Many cheaper colouring matters equal in shade are known.