engraving come under two general
heads: "Half-tone" and "line engraving," the latter being very
generally known as "zinc etching." Zinc etching is the simplest method
of photo-engraving and should be thoroughly understood before one
begins to inquire into the intricacies of the half-tone process. It is
used to reproduce what is known as "black and white" work, or line
drawings. Any drawing or print having black lines or dots on a white
background, without any middle shades, may be engraved by this
process. The old-fashioned "wet-plate" photography is used in making
practically all process plates, either in line or half-tone.

I will describe briefly all the operations gone through in making a
line plate, taking for a subject a map drawn in black ink on white
paper or a head drawn by Charles Dana Gibson,--subjects wide apart in
an artistic way, but of absolutely equal values so far as making the
plate is concerned. The drawing is first put on a copy board in front
of a camera made especially for this work, in whose holder the wet
plate has already been placed by the operator. The subject may be
enlarged or reduced to any desired size, nearly all drawings being
made much larger than they are desired to be reproduced in the plates.
The exposure is much longer than in ordinary dry plate work, generally
lasting in the neighborhood of five minutes. The result is a black and
white negative. That is, the lines that were black in the drawing are
absolutely clear and transparent in the negative, but the rest of the
negative is black. From the photographer, the negative goes to the
"negative-turning" room. Here the negative is coated with solutions of
collodion and rubber cement, which makes the film exceedingly
tough--so tough that it is easily stripped from the glass on which it
was made, and is "turned" with the positive side up on another sheet
of glass. If this were not done, the plate would be reversed in
printing--that is, a line of type would read from right to left, or
backward. After the negative is "turned," it is ready for the etching
room. Here the surface of a sheet of zinc about one-sixteenth of an
inch thick, which has been polished until it is as smooth as plate
glass and without a scratch or a flaw of any kind, is flowed with a
sensitized solution, easily affected by light. The negative is placed
in a printing frame over the sensitized zinc and a print is made. That
is, it is exposed to the sunlight or to a power