Yellow dyes
The principal colouring matters for dyeing yellow, are weld, fustic, and quercitron bark. Yellow colouring matters have too weak an affinity for cloth, to produce permanent colours without the use of mordants. Cloth, therefore, before it is dyed yellow, is always prepared by soaking it in alumine. Oxide of tin is sometimes used when very fine yellows are wanting. Tan is often employed as subsidiary to alumine, and in order to fix it more copiously on cotton and linch. Tartar is also used as an auxiliary, to brighten the colour; and muriate of soda, sulphate of lime, and even the sulphate of iron, to render the shade deeper. The yellow dye by means of fustic is more permanent, but not so beautiful as that given by weld, or quercitron. As it is permanent, and not much injured by acids, it is often used in dyeing compound colours, where a yellow is required. The mordant is alumine. When the mordant is oxide of iron, fustic dyes a good permanent drab colour. Weld, and quercitron bark yield nearly the same kind of colour; but the bark yields colouring matter in greater abundance and is cheaper than weld. The method of using each of these dye-stuffs is nearly the same.