ETCHING. ' 425 



the aqua fortis to bite. This may be diluted to a 

 proper consistence with turpentine, and mixed 

 with lamp-black, that it may be seen better when 

 laid upon the pkite. 



Ectching-ground is used for covering the plate 

 all over with, previous to drawing the lines on it 

 with the needles. It is prepared in the following 

 manner. 



Take of virgin-wax and asphaltum, each two 

 ounces, of black pitch and Burgundy pitch, each 

 half an ounce ; melt the wax and pitch in a new 

 earthenware glazed pipkin, and add to them, by 

 degrees, the asphaltum, finely powdered. Let the 

 whole boil till such time as that, by taking a drop 

 upon a plate, it will break when it is cold, on bend- 

 ing it double two or three times between the fingers. 

 The varnish, being then enough boiled, must be 

 taken off from the fire, and letting it cool a little, 

 must be poured into warm water, that it may work 

 the more easily with the hands, so as to form into 

 balls for use. 



It must be observed, first, that the fire be not 

 too violent, for fear of burning the ingredients ; 

 a slight simmering will be sufficient j secondly, 

 that while the asphaltum is putting in, and even 

 after it is mixed with them, the ingredients should 

 be stirred continually with a spatula ; and thirdly, 

 that the water into which this composition is 

 thrown, should be nearly of the same degree of 

 warmth with it, to prevent a kind of cracking, 

 which happens when the water is too cold. 



The varnish ought always to be harder in sum- 

 mer than winter, and it will become so if it be 

 suffered to boil longer, or if a greater proportion of 

 the asphaltum be used. The experiment above 

 mentioned, of the drop suffered to cool, will de- 



