GRAPHICS. 171 
are now done, and, as in copper-engraving, are to be stopped out with 
varnish. There is then poured upon the plate, in order to wash the oxide 
out of the strokes, a mixture of six parts of water and one part of nitric 
acid: this is left to stand two or three minutes, is then poured off, and imme- 
diately the menstruum is applied with which the second tint is etched. 
The same process is gone through for the other tints. If the plates be very 
soft, the following menstruum may be employed : 3 oz. warm water, 4 grains 
tartaric acid, 4 drops nitric or sulphuric acid, and 1 drachm corrosive subli- 
mate. Every time a plate is bitten in, it is carefully gone over with a 
camel’s hair pencil dipped in clean water, and then immediately dried, in 
order that no oxide may be left in the strokes. Places which are not yet 
deep enough are rebitten, which is done by dipping a clean rag in greatly 
diluted nitric acid (so that the water has merely a sharp acid taste) and passing 
it over the places until they become dull, when the plate is cleaned again. 
The stopping out, even of whole surfaces, is never done with the dabber, 
but always with the pencil, as the dabber is apt to remove the etching- 
ground. As the chief point in etching is to see that the menstruum acts 
precisely the proper time, the light tints must be tried each minute after 
the first biting in; with the deeper shades this is not necessary. The skies 
are bitten in after Cooke’s method ; the plate is inclined a little by means of 
wedges, the darker part lying foremost, and the acid is applied through a 
funnel, in the pipe of which a small stick is placed, and kept constantly in 
a perpendicular position by a string. The acid is let to fall on the darkest 
places, and to drop more rapidly or slowly according to the depth of the 
tint ; this is managed by means of the stick, a tremulous motion being also 
communicated to the acid, until it floats over the whole sky. The etching- | 
liquor should never stand more than one sixth of an inch above the 
plate; for otherwise the design cannot be accurately inspected and judged 
of. The process of biting in and re-biting must be performed in a 
temperature of at least 60° F., and if possible must be finished in the same 
day ; because even in a very well cleaned plate an oxide will form in the 
strokes over night, which will prevent the etching-liquor from workin’ pro- 
perly the following day. 
When the etching is completed, the ground is taken off with the aid of 
turpentine, any remaining oxide is removed from the plate, and its entire 
surface is then rubbed over with very fine emery-paper, which is first worn 
down a little on the back of the plate. By this operation the fine burr 
which is always found on the edges of the strokes is removed. When the 
plate is etched, and has been thoroughly cleaned, it is coated for re-engrav- 
ing with a very thin layer of wax or of mutton-tallow, to prevent any oxide 
from forming in the strokes. Finally, the finished plate must be hardened 
again. This is done in hot olive oil, in which the plate neither warps nor 
eracks. The plate, however, remains in the hot oil only a few minutes, 
after which it is taken out and immediately plunged into cold water, where 
it stays till completely cooled. It is still better to substitute mercury for 
water in the process of hardening, as thereby the grey coating that forms on 
the steel is avoided, and the surface of the plate remains uninjured. 
555 
