1835.] Calico- Printing. 13 



it of an atom of oxygen, and thus renders it capable of com- 

 bining with the lime, and of forming a compound which 

 dissolves in water, and forms a yellow liquid. Where this 

 solution is in contact with the atmosphere, the indigo is 

 revived, assumes its blue colour, and loses its solubility. 

 Hence, the blue scum which always covers the surface. 

 But this scum, in some measure, protects the rest of the 

 vat. When cloth is dipt into this vat it comes out yellow. 

 But from the exposure, the indigo gradually absorbs oxy- 

 gen and becomes blue. The cloth at first, from the mix- 

 ture of the blue and yellow, has a green colour, which 

 slowly deepens into blue. But if, to any parts of the cloth 

 before it be dipped into the vat, something has been applied 

 which has the property of giving out oxygen to the indigo ; 

 all the indigo which would be imbibed by these parts is 

 revived, before it comes in actual contact with the cloth ; 

 and, in the revived state, it is incapable of combining 

 chemically with the cloth, but may be easily washed off. 

 Hence, the parts covered by resist-pastes remain white. 



The following are the principal resist-pastes used by 

 calico-printers : 



1. Blue paste, or vitriol paste consists of a mixture of 

 sulphate and acetate of copper, and the solution is thick- 

 ened with gum-senegal and pipe-clay for the block, and with 

 flour, for the cylinder. When the cloth on which this 

 paste has been printed is dipt into the indigo vat, the in- 

 digo is revived before it has time to reach the surface of 

 the cloth. After dyeing, the piece is passed through weak 

 sulphuric acid, to remove the oxide of copper which has 

 been precipitated on it. 



2. Mild paste consists of sulphate of zinc, gum, and 

 pipe-clay. It is used along with colours which copper would 

 injure, or which would be destroyed by immersion in sul- 

 phuric acid. It resists a pale blue, and the removal of 

 the oxide of zinc by an acid, is not necessary, as it is when 

 copper has been employed 



Sulphate of zinc, as well as all the other metallic salts 

 and all the acids, precipitates indigo from its solution in 

 lime. It does not revive the indigo like the salts of copper ; 

 but when the base of indigo is precipitated, it is not so 

 readily fixed as when in a state of solution. The oxide of 



