The silk when alumed is to be dyed in the decoction of Brazil wood according to the shade required; it is then to be washed and dyed in archil: and it is afterwards washed a second time. After this it is dipped in the blue vat, and wrung and dried with the same accuracy used in greens and blues. For dyeing silk _black_ and some other colours, see Chapters V. and VI. CHAPTER IV. ON SCOURING AND DYEING WOOL. _On the action of alum and tartar upon wool—A pastil or woad vat for blue—To prepare the indigo mentioned in the preceding directions—Rules to judge of the state of the vat—Indications when a vat has had too much or too little lime—To work a vat which is in proper order—On the putrefaction of the woad vat—Methods of dyeing blues—To dye wool, with lac-dye, scarlet, or crimson—To dye worsted yarn a crimson—A preparation of archil to finish the crimson—On dyeing wool scarlet—To dye wool maroon—To dye wool yellow—To dye wool brown or of a fawn colour—To dye wool purple, &c.—To dye wool green—A chemic vat for green woollen—A chemic vat for blue woollen—To dye wool orange, gold colour, &c.—To dye wool black—another process for black without a blue ground—To dye wool grey—Mixture of black or grey with red and blue—On browns, fawns, greys, &c.—On the yellow of quercitron bark—On a full bright yellow from the same bark—Bancroft's murio-sulphate of tin—To dye wool buff—To dye wool peach—To set an Indigo vat for worsted, serge, &c._ Wool is usually scoured for being dyed with stale urine, the staler the better: it is used in the proportion of one part to three parts of water, full as hot as the hands can bear when the wool is worked about in the fluid.—If the wool be in the fleece, what is called its natural yolk, and which is said to preserve the wool from the moth, is of a greasy nature, and is scoured out by the volatile alkali in the urine. If the wool be in the state of spun yarn it has gallipoli, or rape oil, in its thread, the spinner, or rather the comber, using it to render the wool more flexible, &c. It is absolutely necessary that wool, (as indeed every other material to be dyed) should be made very clean and white, if any brilliant or bright colour is to be imparted to it. For this reason it is that the wool is passed two, three, and in some instances even four times through fresh scouring liquors; in the last, and sometimes in that which precedes the last, soap is used in the proportion of from seven to fourteen pounds, and in some instances to twenty one pounds or more, to, a pack of two hundred and forty pounds of wool, according as it is fine or coarse: for superfine colours more than common is used. Worsted requires less than coarse yarn, having less grease and dirt in it.