COGUES. 



when dissolved in turpentine, it becomes a useful 

 substance for giving deep and spirited touches to 

 drawings. 



White Colours. 



Flake White is corbonate of lead, formed by cor- 

 roding lead with vegetable acids, or vinegar. 



White-lead is the same colour as flake white, only 

 of an inferior quality. It is the only white used 

 in oil-painting, and is a very useful colour ; but in 

 water it always turns black, and should never be 

 used. 



Pure carbonate of lime is very useful as a white 

 in water-colours, as it stands perfectly well. 



Egg-shell white, and oyster-shell white, are only 

 egg-shells, or oyster-shells calcined, by which the 

 animal gluten is destroyed, leaving the lime be- 

 hind, which soon attracts the carbonic acid again 

 from the atmosphere. Well washed Spanish white, 

 or common whitening, answers the same purpose. 



Black Colours. 



Lamp black is the soot of oil, collected after it 

 is formed by burning. It is very generally used, 

 both in oil and water, and stands perfectly well. 



Ivory blade is the coal of ivory or bone, formed 

 by giving them a great heat, while they are de- 

 prived 'of all access of air. It is of a more intense 

 black than lamp black. 



Blue blade is the coal from burning vine-stalks 

 in a close vessel. It is like ivory black, with a tint 

 of blue. 



Indian ink has been already described in page 

 346. 



