If the wool is to be dyed in the fleece, it will require a third of its weight of this mordant, but for cloth a fifth will be suf ficient. A bath is to be prepared as hot as the hand can bear, with which the mordant is to be well mixed, and the stuff is to be dipped in it-and stirred ; the same temperature is to be kept up for two hours, and increased a little to wards the end ; after which the stuff is to be taken out, aired, and well washed. A fresh bath of pure water is prepared at the same temperature, to which a suf ficient quantity of the decoction of log wood is added : in this the stuff is im mersed and stirred ; the heat is then in creased to the boiling temperature, and continued so for fifteen minutes, after which the stuff is taken out, aired, and carefully rinsed. If the decoction of one pound oflogwood has been used for eve ry three pounds of wool, and a propor tionate quantity for stuffs that require less, a fine violet colour is produced; to which a sufficient quantity of Brazil wood imparts the shade known in France by the name of prune de Monsieur..
The colours produced by logwood, Brazil, fustic, and yellow wood, may be fixed on wool to advantage by the last mentioned mordant. The alkali of the soap used in fulling is apt to change the colour given by the two first of these substances, but this is remedied by a slightly acid bath a little hot, called the brightening bath, for which sulphuric acid is the best ; the colour after this is as deep, and frequently much brighter, than before the change. Wool dyed by means of this mordant is said tv admit of being spun into a finer and more beauti ful thread than that prepared by alum. if the sulphate of copper is omitted, • more beautifd colours, are produced by fustic and yellow wood, as well as by weld. An orange red is given by mad der with it, but not so deep as with a si milar quantity of alum. When sulphate of copper is omitted, the wool is said to be much harsher, and the mordant pre pared without it yields but indifferent colours with logwood, and in particular with Brazil wood.
Of dyeing Silk violet or purple.
Silk may be dyed violet in two differ ent modes ; the colour produced by the one is called the fine colour, and that by the other the false, the latter of which is dyed by means of archil or Brazil wood. 'When the fine colour is required, the silk must first be passed through a cochi neal bath, and afterwards be clipped in the blue vat. The preparation and dye ing of silk with the cochineal are the same as for crimson, with the omission of tartar and solution of tin, by which the colour is heightened. The quantity of cochineal made use of, is always propor tioned to the required shade, whether it be more or less intense ; but the usual proportion for a fine violet colour, is two ounces of cochineal for each pound of silk. When the silk is dyed, it is wash
ed at the river, twice beetled, dipped in a blue vat, more or less strong in propor tion to the depth of the shade of violet wanted, and then washed and dried, with the precautions which all colours require that are dyed in this vat. If the violet is to have greater strength and beauty, it is usual to pass it through the archil bath ; without this, light shades would be too dull.
When silk has been dyed with cochi neal as above directed, only a very light shade is requisite for purple ; the shades which are deepest are dipped in a weak blue vat, but those which are to be lighter, it is sufficient to dip in water in corporated with a small quantity of the liquor of the vat, because in the vat it self they would acquire too deep a tinge of blue, however weak it might be. The light shades of this colour, as gilly flower, peach-blossom, &c. are produced in this manner, by diminishing the quantity of cochineal.
The false violet colour of the greatest 'beauty is given to silk by archil, in the various ways used for producing it ; the bath of which is to have its strength pro portioned to the colour required. The silk having been beetled at the river, after scouring, is turned in the archil bath on the skein sticks ; and when the colour is deemed sufficiently deep, a pattern is tried in the blue vat, to ascertain whether it takes the violet colour intended to be produced. If the shade is of the proper depth, the silk is beetled at the river, and dipped in the vat in the same way as for the fine violet.colours ; and less either of the blue or of archil colour is given, according as the violet is intend ed to have the blue or red shade predo minant.
A violet colour may be imparted to silks by immersing them in water im pregnated with verdigris as a substitute for aluming, and next giving them a bath of logwood, in which they assume a blue colour ; which is converted into a violet, either by dipping them in a weaker or stronger solution of alum, or by adding it to the bath ; the alum imparts a red shade to the colouring matter of the logwood. This violet possesses but little beauty or durability ; but if the alumed silk be im mersed in a bath of Brazil wood, and next in a bath of archil, after washing it at the river, a colour is obtained, possess ing a much higher degree of beauty and intensity. M. Decroizilles' process, above related, for dyeing wool, suc ceeds equally well, according to his ac count, in communicating a violet colour to silk.