422 Mr. E. Turrell's Mensh'uumjbr Biting-in on Steel Plates. 



superior hardness of the metal, which of course would offer 

 greater i-esistance to the action of the graver than copper : but 

 as most or all the engravings of the present time are a mix- 

 ture of etching and graving united, it was of course equally 

 necessary for tiie artist to be able to etch and bite-in upon de- 

 carbonized steel, as well as to cut with the graving tool. 



In order to form a just idea of the difficulties that occur in 

 etching and biting-in upon steel plates, it will be necessary to 

 state a few facts relative to etching upon copper. 



The visual method is to cover the copper plate with a coat 

 of varnish, commonly called etching ground ; and when the 

 lines that are necessary to represent the subject are cut through 

 the varnish with a point or needle, a border or rim of soft wax 

 is raised round the sides of the plate, and nitrous acid, suffi- 

 ciently diluted with water, is poured upon the whole surface, 

 and immediately a corrosion of the copper takes place in those 

 parts or lines where the varnish has been removed or cut 

 through. The action of the acid is at the same time rendered 

 obvious to sight by the continual formation and disengagement 

 of bubbles of the nitrous gas on all the etched parts, thus in- 

 dicating to the artist how the process is going on. 



Various acids have been tried for this purpose, both singly 

 and compounded in various proportions ; but experience has 

 proved that very pure nitrous acid is superior to any com- 

 pound that has hitherto been produced, and I believe it is also 

 superior to any other acid that can be used singly; for there 

 is one requisite that is absolutely necessary and indispensable, 

 namely, that whatever acid is used, it should not only have a 

 powerful affinity for the copper, and by its chemical action 

 corrode and deepen the etched lines, but it should also be ca- 

 pable of holding the oxide formed in perfect chemical solu- 

 tion, otherwise the lines would soon be choked up by a depo- 

 sition of the oxide so formed ; as the deposition increased, the 

 oxide would press upon the edges of the etching varnish and 

 loosen it, by which means a partial corrosion would take place 

 under it, and shallow lines would be the consequence. The 

 lines produced under such circumstances are also generally 

 rough and uneven on their edges. The process just described 

 is technically called biting-in, and such a production would be 

 called a bad biting. On the contrary, when the oxide of cop- 

 per formed during the process is immediately dissolved in the 

 fluid that forms it, a fresh surface at the bottom of the line is 

 continually offered to the acid to act upon, and then the cor- 

 rosion produces the very best effect, that is to say, very deep 

 lines, with beautiful clear and even edges. 



When etching upon steel was first introduced, great diffi- 

 culty 



