ful electric light, and
the light shines through the transparent parts of the negative, and
hardens the sensitized surface; while the black part of the negative
protects the sensitized surface from the action of the light. The
plate is next "rolled up" with a lithograph roller which distributes a
thin coating of etching ink over the entire surface. The plate is then
washed off carefully by the operator, but the ink adheres to all
portions of the plate that have been acted upon by the light. We now
have a fully developed print on the highly polished surface of the
zinc that is an exact reproduction of the original drawing. It is now
necessary to make this print acid proof, and this is done by covering
the plate with a coating of very fine resinous powder, called
"dragon's blood," which adheres to the printed portions of the plate.
The plate is subjected to enough heat to melt this powder, and is then
ready for the acid bath.

A strong solution of nitric acid is used for etching zinc plates. This
acid is placed in trays, which are rocked constantly, either by power
or by hand, while the plate is being etched. The melted dragon's
blood makes a perfect acid resistant and the acid, therefore, does not
affect the print (or picture itself), but eats away the bare surfaces
of the metal between the black lines and the dots. When this etching
has proceeded far enough to make a plate that may be used in printing,
the lines and dots of the picture stand up in bold relief, while the
metal around these lines and dots has been eaten away to a
considerable depth.

There are many details that cannot be described in a short article,
but these are the principal operations gone through in etching the
plate. One very important detail in etching is to prevent
"undercutting." It is obvious that if the acid will eat down, it will
also eat sidewise. The acid resistant is only on the surface. If means
were not taken to prevent it, as soon as the acid got below the
surface, it would begin to eat in under the print and the lines and
dots of the picture would disappear; therefore, as soon as the plate
has had its first "bite," it is taken from the acid, dried, and
dragon's blood is brushed against the sides of the lines. This powder
is then melted and the plate given another etching. While the plate is
being etched down, it is removed from the acid several times, and the
sides of the dots and lines are again protected. After leaving the
etching