THE YOUNG SCIENTIST. 
85 
breath remains for some time on the sur- 
face, the acid ma^^ be applied with safety ; 
but if it rapidly passes off, then it is not 
safe. It is a consideration in biting to 
produce a clear deep line. This desirable 
quality is more likely to be produced by 
pouring a depth of at least half an inch of 
acid on the plate, and by carefully remov- 
ing, with a very soft feather, the small 
globules which will be seen to congregate 
on the surface of the plate. The biting is 
the most uncertain portion of the process 
of etching, and the most experienced 
are liable to fail. Tor general purposes, 
however, a very little practice will ensure 
success. When it is considered that the 
etching has been bit to a sufficient color, 
it is necessary to remove the bordering 
wax by heating the plate, and then clear- 
ing it with spirit of turpentine, and after- 
wards rubbing with oil and a soft rag ; it 
will then be necessary to send to the cop- 
perplate printer for a proof. 
The process of copperplate-printing is 
■exactly the reverse of printing from wood- 
cuts and type. In the latter the ink is 
passed from the surface of the block, etc., 
to the paper by means of pressure ; in the 
former the impression is delivered from 
an incised line. In copperplate-printing 
the whole of the surface of the plate, and 
also the lines, are covered and filled with 
ink ; the printer then (with the assistance 
■of heat and whiting), by passing his hands 
•gently and repeatedly over the surface of 
the plate, removes the ink from the entire 
:surface, but leaves it in the lines or 
scratches. Damp paper is then passed 
through the rollers of the press, between 
the upper roller and the plate are several 
layers of cloth, and the ink from the lines 
is thus placed on the paper. If it is found, 
on examining the proof, that some por- 
tions of the etching are not sufficiently 
dark, the fault may be remedied by ''re- 
biting." 
The lines on the plate must he most care- 
fully cleaned from all remains of printing 
ink, or any substance that would interfere 
with the proper application of the etching- 
ground or acid. It is best to wash the 
plate well with spirit of turpentine and a 
perfectly clean rag; then rub the lines 
-and surface of the plate with spirit of 
turpentine and bread, and afterwards 
with spirit of turpentine and whiting; 
after that with whiting and bread. If 
any portions of whiting remain in the 
lines, it can be removed by wash-leather 
and soft bread : the object of all this care 
is to free the lines from any impediment 
to the action of the acid, and to enable 
the student to cover the surface of the 
plate with etching-ground, so that, the 
surface being protected from the action of 
the acid, but the lines left unfilled, the 
parts which are already sufficiently dark 
can be stopped up with varnish, and acid 
applied in the regular manner, and an 
increase of depth be got on any part of 
the plate that may be required. The 
principal things to be attended to in lay- 
ing a rebiting ground are, that the lines 
shall be left free from etching-ground, 
and the surface completely covered; if 
this is not attended to, the acid will fill 
the parts of the plate that are not covered 
with varnish or ground with numerous 
small holes, which will certainly produce 
impure tints ; this appearance is known 
among engravers by the name of foul 
biting. The dabber used to lay the etch- 
ing-ground may be used tor the rebiting- 
ground ; but it is perhaps well not to ap- 
ply so much heat, as the ground, if too 
thin, is liable to run into parts of the 
lines; this produces, perhaps, as ill an 
effect as foul biting, for if the acid is 
placed on such a ground, it will cause an 
unsteady or rotten appearance, by biting 
the lines which are clear to a greater 
thickness than others. 
Considerable finish may also be got by 
using the" dry-point," which is nothing 
more than an etching-point made sharper 
than it is required for the purpose of 
etching ; indeed, it is used for scratching 
such lines into the copper as will throw 
off an impression. On examining a line 
made with the dry-point, it will be found 
that the metal is not removed as if cut 
with a sharp graver, but merely pushed 
to one side ; if this, which is called the 
burr, is allowed to remain, it will, by its 
roughness, pollect the ink and form a blot 
on the impression. To remove this burr 
it is necessary to use the scraper in such 
a manner as not to drive the burr back 
