sh it, first with pumice stone and water, then with snake stone,
jewelers' rouge. Plates can be purchased in a high state of
preparation from the engravers. Having prepared the copper-plate, well
rub it with salt and water, and then with the silvering powder. No
kind answers better than that used by clock-makers to silver their
dial-plates. It is composed of one part of well washed chloride of
silver, five parts of cream of tartar, and four parts of table salt.
This powder must be kept in a dark vessel, and in a dry place. For a
plate six inches by five, as much of this composition as can be taken
up on a shilling is sufficient. It is to be laid in the centre of the
copper, and the figures being wetted, to be quickly rubbed over every
part of the plate, adding occasionally a little damp salt. The copper
being covered with the silvering is to be speedily well washed in
water, in which a little soda is dissolved, and as soon as the surface
is of a fine silvery whiteness, it is to be dried with a very clean
warm cloth. In this state the plates may be kept for use. The first
process is to expose the plate to the heat of a spirit flame, until the
silvered surface becomes of a well-defined golden-yellow color; then,
when the plate is cold, take a piece of cotton, dipped in very dilute
nitric acid, and rub lightly over it until the white hue is restored,
and dry it with very soft clean cloths. A weak solution of the
hydriodate of potash, in which a small portion of iodine is dissolved,
is now passed over the plate with a wide camel's hair brush. The
silver is thus converted, over its surface, into an ioduret of silver;
and in this state it is exposed to light, which blackens it. When dry,
it is to be again polished, either with dilute acid or a solution of
carbonate of soda, and afterwards with dry cotton, and the smallest
possible portion of prepared chalk: by this means a surface of the
highest polish is produced. The rationale of this process is, in the
first place, the heat applied dries off any adhering acid, and effects
more perfect union between the copper and silver, so as to enable it to
bear the subsequent processes. The first yellow surface appears to be
an oxide of silver with, possibly, a minute quantity of copper in
combination, which being removed leaves a surface chemically pure.

Another Method.--The best and simplest mode with which we are
acquainted is to divide an earthenware vessel with a diap