426 Mr. C. Turner on the Invention, Progress, and Advantages 



The. proportions of the acids and the alcohol are as follows : 

 Take four parts, by measure, of the strongest pyroligneous acid 

 (chemically called acetic acid), and one part of alcohol, or 

 highly-rectified spirits of wine ; mix these together, and agitate 

 them gently for about half a minute; then add one part of 

 pure nitric acid ; and when the whole are thoroughly mixed 

 the menstruum is fit to be poured upon the etched steel 

 plate. 



When the menstruum is compounded in these proportions, 

 very light tints will be sufficiently corroded in about one mi- 

 nute, or one minute and a half, and a considerable degree of 

 colour will be produced in about a quarter of an hour. But 

 the effect may be produced much quicker by the addition of 

 more nitric acid, or it may be made to proceed much slower 

 by omitting any convenient portion thereof. 



The plate, when the mixture is poured off, should be in- 

 stantly washed with a compound made by adding one part of 

 alcohol to four parts of water ; and the best material for stop- 

 ping out any part that is sufficiently corroded is pure asphal- 

 tum dissolved in essential oil of turpentine, which of course 

 must be of sufficient consistence to flow freely from a hair 

 pencil. It may be necessary to inform those engravers that 

 use the common Brunswick-black to stop out the bitings on 

 copper plates, that it is a very improper article to use on steel 

 plates; because, as the asphaltum and oil of turpentine, of 

 which it is principally composed, do not render it sufficiently 

 drying, these ingredients are digested with a small quantity of 

 spirit of wine, which has a great tendency to unite with the 

 biting menstruum above described, and thereby cause foul 

 biting. 



As I attach considerable importance to the purity of the in- 

 gredients of which my menstruum is composed, I beg leave to 

 impress on my brother artists the necessity of strict attention 

 to this circumstance : I have myself obtained the ingredients 

 in a state entirely to my satisfaction from Mr. Desormeaux, 

 16, Charlton-street, Somerstown. 



LXVII. On the Invention, Progress, and Advantages of the Art 

 of Engraving in Mczzotinto upon Steel. By Mr. Charles 

 Turner, of Warner-street, Fitzroy-sqnare* . 



nr^HE discovery of a method of engraving in mezzotinto upon 



■*- steel may be justly regarded as one of the most fortunate 



occurrences in the history of the graphic arts. In the infancy 



* From the Transactions of tlie Society of Arts. 



of 



