The application of oil, which heightens the black, and imparts softness to the stuffs, is given to such articles as cotton velvet by means of brushes, which are slightly imbued with it. _Berthollet._ We may add here, that an iron liquor called _tar-iron liquor_, prepared from the acid obtained from tar, (the acetic acid we presume) is now well known in commerce, but we have not room, nor does it appear necessary, to describe the method of making it; it is much used in preparing mordants for black and other colours by the dyers and printers of silk. This iron liquor may be obtained of Blake, North Street, Back Church Lane, St. George's in the East, London. See _M'Kernan_. _To dye cotton_ VIOLET. Pass the skeins through the black vat and dry them, then pass them through a decoction of galls and dry them again, then through a decoction of logwood, then of alum and verdigris, washed off, and dried. Or thus: by the black vat liquor, that is, the liquor of old iron and alder bark in some cases. Let the vat liquor be prepared from the iron hoops, vinegar, rye, or coarse bran, described in page 108. By this liquor it is easy to procure all the violet shades from the pansy flower up to the lilac and violet. The goods must be first blue-vatted and dried, then galled and dried, then passed through the iron liquor, then maddered, then washed off, and dried; the liquor must always be kept much below a boiling heat, as this heat makes the colour obtained from madder brown: whatever drugs require boiling must be prepared by a decoction previously made. For some shades sulphate of copper is used; for others verdigris, saltpetre, and alum. To dye to the pattern the preparations should be always of one given strength, and all solutions of mordants the same. The time of working the goods in the dye must be regulated by the fulness or lightness of the pattern; and the quantities of the various drugs, &c. used much or little accordingly, reserving patterns of processes, with the particulars of such processes noted down. In proportion to the number of these upon record, and with strict attention to the subject, a good pattern dyer is formed. Time and practice are, however, absolutely necessary, with a delight in the business: for without a pleasure in dyeing no one can become a good or an eminent dyer. In many of the branches of this art there are, it is true, labour and pains in abundance; but there is also a portion, and that not a small one, of pleasure in others, which will counterbalance the care, anxiety, labour, and fatigue inseparable from this useful and important occupation, and which so strikingly exhibits the science and ingenuity of man. _To dye cotton_ RED.