The yellow lake known as Dutch pink is prepared from yellow (Persian) berries, by boiling the crushed berries with water and mixing the extract with a solution of alum. The lake is then precipitated by the addition of powdered chalk. As a rule, 500 parts of water are used to 100 parts of berries, 20 parts of alum are added to the decoction, and the mixture poured upon 75 parts of finely powdered chalk. The liquid is decanted off, the residue filtered, washed and dried. Commercial Dutch pink is made from a mixture of the decoctions of yellow berries, quercitron bark and turmeric, to which the alum solution is added, and then chalk. The precipitate is made into conical lumps, which are sold as Dutch pink, and used for ordinary painting and for colouring leather. =Weld Lake.=—The dyers’ weld (_Reseda luteola_) contains a yellow colouring matter formerly much used in dyeing; a yellow lake can also be obtained from it. When weld is boiled with water a deep yellowish green decoction is obtained, from which yellowish-green flocks separate on cooling. The lake can be obtained from all parts of the plant except the root, the flowering shoots giving the largest yield of colour; the lake is generally precipitated by alumina. Equal parts of weld and alum are boiled with water until the latter is dissolved and the liquid is coloured deep yellow; the hot solution is quickly filtered through a thick linen cloth and soda solution gradually added in small quantities with continual stirring so long as effervescence follows. Alum entirely free from iron is required to produce a bright yellow lake; a small quantity of iron has great influence on the shade. Weld contains more or less tannin, which gives very dark blue or green compounds with iron salts, the production of a very small quantity of which suffices to convert the yellow shade into an ugly dirty colour. Chalk may be used instead of soda to precipitate the alumina; in this case the precipitate will contain calcium sulphate in addition to the alumina compound of luteolin. Weld lake may be used in oil, or size, or as a water colour. =Gamboge Lake.=—Crude gamboge is the dried sap of certain East Indian trees; it is used as an artists’ colour, but only in water; for use in oil it is converted into a lake. A particular treatment is necessary to obtain a handsome lake. Gamboge is treated for several days with water and the soft mass ground on the slab or in a mill until it forms a uniform paste, which is mixed with water to a thick liquid, which is then put through a fine sieve. A hot solution of alum is then added in the proportion of three parts of alum to one part of gamboge, the mixture is boiled in a wooden vessel and two parts of nitric acid added whilst well stirring; finally a dilute solution of potash is added in small quantities until the liquid solidifies to a jelly, which is spread out in thin layers on filter cloth, well washed with water and dried at a gentle heat.