16 



Dr. Thomas Thomson 



4. Cochineal Pink. — After the 

 black in this pattern has been pro- 

 duced in the way already detailed, 

 it receives an alum mordant on those 

 parts which are intended to become 

 pink. It is then cleansed and dyed 

 in cochineal, in a similar way as 



when cloth is dyed with madder. The cochineal does not 

 tinge the ground as madder does ; and therefore, does not 

 require, nor is it of sufficient permanence to bear the same 

 clearing operations. So much colouring matter does the 

 cochineal insect contain, that one ounce is sufficient to dye 

 fifteen or twenty yards of such a pattern, as No. 4. 



5. Logwood Black. — The same alumi 

 mordant which forms a red with 

 madder, becomes black when dyed 

 with logwood. The iron mordant 

 has the same property ; but it forms 

 a brownish, and less pleasing colour. 

 Rinsing the piece of goods in hot 

 bran and water, is sufficient to remove the tinge of los:w< 

 from the white ground. 



6. The two shades of colour in 

 No. 6, are obtained from mixed alum 

 and iron mordants, dyed in a mix- 

 ture of madder and quercitron bark. 

 The mode of producing the black 

 and white figures on it, will be ex- 

 plained afterwards. 



7. Prussian Blue — The iron mor- 

 dant is applied, and the cloth cleansed 

 in the way already described. It is 

 converted into prussian blue of va- 

 rious hues, by immersion in cold 

 prussic acid. This acid is liberated 

 from a weak solution of prussiate of 

 potash, by an equivalent of sulphuric acid. A more 

 convenient process for this colour, is now employed, 

 and it will be explained, when we come to speak of steam 

 colours. 



