perfect a protection as any asphaltum varnish."

Mr. Smillie heats his bath on the plate-warmer, but not to exceed 80 deg.,
or at most 90 deg. Such a bath of hot mordant acts much more quickly than
a cold acid bath, less than two minutes being sufficient for the lightest
lines.

[17] (p. 50.) Gravers are of different shapes, according to the nature
of the line which they are intended to produce. They are sometimes kept
at the hardware-stores, as, for instance, by A. J. Wilkinson & Co., 184
Washington St., Boston. This house also issues an illustrated catalogue
of engravers' tools.

[18] (p. 52.) M. Lalanne, it seems to me, does not do full justice to
zinc plates. Very delicate lines can be bitten on zinc if the acid is
sufficiently weakened. I have found that one part of nitric acid to
eight parts of water, used on zinc, is about equal to one-half acid and
one-half water, used on copper for about the same length of time. Zinc
plates can also be bought of Mr. Geo. B. Sharp, 45 Gold St., New York.
As to the length of edition that can be printed from a zinc plate, see
Note 27.

[19] (p. 52.) This is not strictly correct. The "maniere de crayon," as
practised by Demarteau and others, differs materially from soft-ground
etching. A ground was laid and smoked as usual, and on it the drawing
was produced, by a variety of instruments, such as points, some of them
multiple, the roulette, the mattoir, etc.

[20] (p. 55.) There is another method of getting what may be called a
proof, i. e. by taking a cast in plaster. Ink your plate and wipe it
clean, as described in Note 22, and then pour over it plaster-of-Paris
mixed with water. When the plaster has hardened it can easily be
separated from the plate, and the ink in the lines will adhere to it. To
make such a cast you must manage a rim around your plate, or you may lay
it into a paper box, face upward. Mix about half a tumbler full of water
(or more, according to the size of the plate) with double the quantity
of plaster, adding the plaster, little by little, and stirring
continually. When the mixture begins to thicken pour it on the plate,
and if necessary spread it over the whole of the surface by means of a
piece of wood or anything else that will answer. Then allow it to
harden.

[21] (p. 55.) The chafing-dish and the ball (or dabber) are now replaced
by the gas flame and the inking-roller in most printing establishments.
But if you desire to do your own proving, you w