identical network of lines in red chalk representing his key. He
proceeds to draw each color-plate successively, at all times adhering
closely to the red chalk outlines, filling in with tusche where full
strength of the color is required and using lithographic crayon or the
stipple process to reproduce the various gradations of this color in
order to secure the full color value of each printing. The register
marks are ruled in on each stone corresponding to those on the key, so
that the prover or printer has these marks in the same identical
position on each and every color as a guide for register.

As each stone is finished it is etched; that is, treated with a weak
solution of nitric acid and gum-water, in order to remove all
accidental traces of scum from its surface, and to prepare it for
printing. Then proofs are made, which serve as a guide to the
lithographer during the progress of his work, and finally as a guide
to the transferrer and to the printer. The proving is done on a hand
press, and it is here that we have our first glimpse of chemical
printing, which, notwithstanding its simplicity, seems so mysterious
to one uninitiated in its secrets.

The writer recollects his own first experience. A stone had just been
placed fresh from the etching trough in the bed of the press, when, to
his amazement, the prover deliberately proceeded to eliminate every
trace of the drawing with a sponge saturated with turpentine. After
drying the stone by means of a fan, he passed over the surface a
sponge soaked in water, then applied black ink with a roller, when
behold, the drawing was restored in its entirety. The solution is very
simple: the greasy matter is absorbed and held by the stone and in its
turn repels water and attracts grease.

An impression is made with black printing ink on paper by passing it
through the hand press. The black impression approved of by the
lithographer, the stone is again cleaned with turpentine and proved in
the color required, and so with each color-plate, until the proof is
complete. When photography is employed, the half-tone negative takes
the place of the key. Prints are made from a reversed negative on the
sensitized surface of the stone, or on as many stones as the
color-plates require, and then manipulated by the lithographer, who
adds or modifies strength with his "tusche" or crayon, and scrapes or
washes out lights where necessary. The various modes of procedure are
too diverse to