Stilk-lac consists of twigs of several kinds of trees encrusted with a resinous matter produced by the puncture of an insect (the coccus lacca). This, triturated with water and dried, forms seed-lac. The seed-lac heated and pressed in cotton bags forms shell-lac. Lac-dye is the colouring matter extracted from stick-lac by water, evaporated to dryness with the addition of earthy matters, and formed into square cakes. Seed-lac and shell-lac are chiefly used* in varnishes, dissolved in rectified spirit, methylated spirit, or rectified wood naphtha. The alcoholic solution is rendered paler, so that it may be used for polishing light-coloured woods, by digesting it in the sun, or near a fire, for 2 or 3 weeks, with good animal charcoal, and then filtering it through paper in a funnel heated with hot water. Shell-lac may be bleached by dissolving it in a solution of potash or soda, and passing chlorine into the solution. The precipitated lac is collected and well washed. Kastner directs 3 parts of carbonate of potash to be dissolved in 24 of water, and 3 of lime added, and the whole digested in a close vessel for 24 hours. The clear liquor is poured off, and boiled with 4 parts of shell-lac. When cold, dilute with 4 times its bulk of water, and filter; then add chloride of lime, and afterwards diluted hydrochloric acid. * Methylated spirit is now almost invariably used for this purpose.