Weld is most commonly used in dyeing yellow. For the preparatory bath for dyeing wool this colour, Hellot directs four ounces of alum, and only one of tartar, to be used for every pound of wool.
For the dyeing bath, the weld is boiled inclosed in a thin linen bag, in the pro portion of from three to to six pounds for every pound of cloth ; it is kept from ris ing by a wooden cross : some dyers add a little quicklime and ashes, which height en the colour, but render it less capa ble of resisting acids. Lighter shades of colour may be obtained by dyeing after deeper ones, adding water after each dipping, and keeping the bath at a boil ing heat. These are not so lively as when fresh baths are used with a suitable pro portion of weld. Alum renders the shade psler and more lively, tartar still paler, but sulphate of iron causes it to incline to brown.
Poerner recommends a similar prepa ration for this dye to that for scarlet, by which the colour will be brighter, more permanent, and lighter.
Dr. Bancroft states quercitron bark to be the cheapest and hest substance for dyeing wool yellow. For its use the fol lowing process is directed. The bark, with an equal weight, or one-third more, of alum, is to be boiled for about ten minutes, in a suitable proportion of wa ter; the stuff previously scoured is then immersed in the bath. The higher co lours are dyed first, and afterwards the pale straw colours. The colour may be considerably heightened, by passing the unrinsed stuff a few times through hot water, to which one pound and a half of clean powdered chalk has been added for every hundred pounds of stuff.
The bark in boiling should be tied up in a thin linen bag, and suspended in the liquor, after having been first reduced to powder. This is the cheapest and quick est process ; but the colour will be fuller and more permanent, if the stuff is first boiled for an hour and a quarter in a bath of a sixth or an eighth of its weight of alum, dissolved in a proper quantity of water, and be then, without being rins ed, immersed in the dyeing bath, form ed by a weight of powdered quercitron bark equal to that of the alum, tied up in a linen bag, in clean hot water: it is to be turned through the boiling liquor in the usual manner, till its colour appears suffi cient. One pound of clean powdered
chalk, for every hundred pounds of stuff, is then to be mixed with the dyeing bath, and the operation is to be continued for eight or ten minutes longer. The addi tion of the chalk heightens and brightens the colour.
To give a beautiful orange-yellow to woollen stuff's, ten pounds of quercitron bark tied up in a bag, for every hundred pounds of stuff, are to be put into the bath with hot water. At the end of six or eight minutes, an equal weight of mu rio-sulphate of tin is to be added, and the mixture to be well stirred for two or three minutes. The cloth, first scoured, and completely wetted, is then immers ed in the dyeing liquor, and briskly turn ed for a few minutes ; by this process the highest, yellow may be produced in less than fifteen minutes.
High shades of yellow are given by young fustic and nitro-muriate of tin, but they are less pernianent, less beautiful, and more costly than those obtained from the above bark.
Of dyeing Silk yellow.
To dye silk a plain yellow, in general, weld alone is used. The silk is first scoured with soap, in the proportion of twenty pounds of soap to the hundred of silk, then alumed, and washed.
The dyeing bath is prepared with two pounds of weld to every pound of silk, which, having boiled for fifteen minutes, is to be passed into the vat through a sieve or cloth. When the temperature is as high as the hand can bear, the silk is introduced, and turned, until it ac quires an uniform colour ; during this time the weld is to be boiled a second time in fresh water ; one half of the first bath is then taken out, and its place sup plied with a fresh decoction. The tem perature of the fresh bath may be a little higher than that of the former, but should not be too great, lest the colour already fixed be dissolved. The stuff is to be turned as before, and then taken out of the bath. Soda is to be dissolved in a part of the second decoction, and a larger or smaller quantity of the solution is to be added to the bath, according to the intensity of the shade wanted. The co lour is examined by taking out a skein and wringing it.