DYEING. 



is necessary to change the green colour, 

 given the stuff' by the bath, to a blue. 

 Wool and cloth dyed in this manner, 

 ought to be carefully washed, to carry off 

 the loose colouring matter; and those 

 which are of a deep blue ought to be 

 even fulled with soup, which cleanses 

 them effectually, without injuring the.co- 

 lour. 



A vat which contains no woad is called 

 an indigo vat ; the vessel used for this 

 preparation is of copper, into which is 

 poured, according to its capacity, water; 

 in forty pails of which, six pounds of 

 potash, twelve ounces of madder, and 

 six pounds of bran, have been boiled; six 

 pounds of indigo, ground in water, are 

 then put in, and after raking it carefully, 

 the vat is covered ; a slow fire is to be 

 kept up round it. Twelve hours after it 

 is filled, it is to be raked a second time, 

 which is to be repeated at similar inter- 

 vals of time, till it comes to a blue, which 

 will generally happen in forty-eight hours. 

 If the bath be well managed it will be of 

 a fine green, covered with coppery scales 

 ami a fine blue scum. In this vat the in- 

 digo is rendered soluble in the water by 

 the alkli instead of lime; the operation 

 ot dyeing with it is the same as the pre- 

 ceding. 



Hellot describes two vats, in which the 

 indigo is dissolved by means of urine. 

 Madder is added to them, and in the one 

 vinegar is put, 1n the other alum and tar- 

 tar, of each an equal weight to the indigo. 

 The quantity of urine ought to be very 

 considerable. It is probable the indigo 

 is dissolved in them by the ammonia form- 

 ed in the urine. These vats are not so 

 good as those before described ; less 

 work can be performed with them, BO 

 that they are adapted only to small dye- 

 houses. 



The colourdyed by a solution of indigo 

 in sulphuric acid is called Saxon blue, 

 from having been discovered at Gros- 

 senhayn, in Saxony, by Counsellor Barth. 

 M Poerner, who has paid great attention 

 to this preparation, directs four parts of 

 sulphuric acid to be poured on one of in- 

 digo, in fine powder : the mixture is to 

 be stirred for some time. After having 

 stood twenty-four hours, one part of good 

 dry potash in fine powder is^ded ; the 

 whole is to be again well stirred, and 

 having stood twenty-four hours longer, 

 more or less water is added gradually. 



To dye Saxon blue, the cloth is pre- 

 pared with alum'and tartar ; a greater or 

 less proportion of indigo is put into the 

 bath, according as the shade required is 



deep or light ; for deep shades the stuff 

 must be passed several tim<_ through the 

 bath ; light shades may be dyed after the 

 deep ones, .but they have more lurtre 

 when dyed in a fresh bath. 



Of dyeing Silk blue. 



Silk is dyed blue by the indigo vat be- 

 fore described. In general a larger pro- 

 portion of indigo is put in than is there 

 directed, but nearly the same quantities 

 of bran and madder. Macquer says, that 

 half a pound of madder for every pound 

 of potash makes the vat greener, and the 

 colour more fixed. When the vat is 

 cotae to about two pounds of potash, 

 three or four ounces of madder should be 

 added ; it should then be raked, and in 

 four hours it will be fit for dyeing. Its 

 heat should be just what the hand can 

 bear without pain. The silk is prepared 

 for this bath by being boiled with thirty 

 pounds of soap for every hundred pounds 

 of silk, and being afterwards well cleans- 

 ed from it by two or more beetlings in a 

 stream of water. As the silk is very lia- 

 ble to take the colour unevenly, it is ne- 

 cessary to dye it in small portions ; the 

 workman dips each hank separately, and 

 when he has turned it once or twice in 

 the bath, he wrings it strongly over it, 

 and airs it, to turn the green colour to a 

 blue ; when the green is thoroughly 

 changed, he throws it into some cleaV 

 water, after which he wrings it several 

 times with the pin. Care must be taken 

 tiiat the silk dyed blue dry speedily. In 

 the winter, and in damp weather, it should 

 be dried in a chamber heated by a stove, 

 where it should be hung on a frame kept 

 in constant motion. When the bath grows 

 weak a pound of potash, an ounce of 

 madder, and an handful of bran well 

 washed, are added. Indigo is also put 

 in when it appears to be wanted. Some 

 dyers use vats grown weak to dye light 

 shail es, but fresh vats give a more beau- 

 tiful and permanent colour. 



As indigo alone cannot give a deep 

 blue, the silk must be prepared by re- 

 ceiving a ground, or other colour, pre- 

 vious to dyeing. For the Turkey blue, a 

 very strong archil bath is first given ; and 

 for the French royal blue, a weaker one 

 of the same kind. Cochineal is used also 

 for the ground of another fine deep blue, 

 which is more permanent. Verdigris and 

 logwood are also used for a preparatory 

 colour, but produce a blue that is not per- 

 manent. It might be rendered more last- 

 ing, by making the shade lighter than 



