14 Dr. Thomas Thomson on [Jan. 



zinc with the gum and pipe-clay, acts mechanically in 

 keeping it at a distance. 



3. Red paste consists of the alum mordant already de- 

 scribed, mixed with acetate of copper, gum, and pipe-clay. 

 It resists pale blues, and the alumina remains upon the 

 white portions of the cloth, to be afterwards dyed red, with 

 madder or yellow by quercitron bark. 



4. Neutral paste is a name given by printers, to a com- 

 pound of lime juice, sulphate of copper, gum, and pipe- 

 clay. It resists during a short dip in the blue vat ; and 

 the lime juice gives it the property of remaining white 

 when the piece is dyed in madder, even when the preced- 

 ing red paste goes over it. This acid also prevents the lime 

 of the blue vat from precipitating copper upon the cloth, 

 which would cause the parts to assume a deep brown tinge 

 when dipt into the madder vessel. 



5. Chrome yellow resist paste consists of a mixture of a 

 salt of copper, to resist the blue vat with a salt of lead, to 

 produce a yellow with bichromate of potash, after having 

 been dyed in the blue vat. 



The preceding observations were necessary, to give the 

 reader an idea of the various processes, followed by the 

 calico-printers, and with the rationale of them. I shall now 

 proceed to explain the different colours. And both the 

 simplest and most intelligible method of proceeding seems 

 to be, to place pieces of printed calico before the eyes of the 

 reader, and describe the way in which the colours on them 

 have been produced. We shall begin with the simplest 

 colours, and proceed gradually to more^omnlex onps 



1. Madder Red. — The alum mor- 

 dant described above, is made into a 

 paste, and printed on the cloth by 

 the cylinder. After being dried and 

 exposed in a warm room, till the 

 alumina has had time to leave the 

 acid with which it was united, and J 

 combine with the cloth, it is passed through a hot mixture 

 of cow's dung and water. It is then washed in cold water, 

 and agitated a second time in the same hot mixture. After 

 being thus freed from all soluble or loose matter, it is dyed 

 in madder. This process consists in the exposure of the 



