arts
Water 500 parts

Rub the alkali and the naphthol with a little water in a mortar and add
the remainder of the water.

FOR ORANGE.
Resorcin 3 parts
Water 500 parts

When dissolved add

Caustic potassa 5 parts

FOR YELLOW.
Carbolic acid, cryst 5 parts
Water 500 parts

FOR PURPLE.
Naphthylamine 6 parts
Hydrochloric acid, in 6 parts
volume

Mix in a mortar, then add

Water 500 parts

FOR BLACK.
Eikonogen, white crystals 6 parts
Water 500 parts

Pulverize the eikonogen, add the water and, at the same time, the material
on its removal from the printing frame, and keep in motion until the
development is effected.

FOR BROWN.
Pyrogallol 5 parts
Water 500 parts

After the development, which requires but a few moments, it suffices to
wash the material to fix the image by eliminating the soluble compounds.
However, for purple the material should be passed in a dilute solution of
tartaric acid and not washed afterwards; it should remain acid.

When it is desirable to obtain an impression in several colors, the
various developers are thickened with starch, then locally applied with a
brush on the image, which is always visible after exposure.

For printing on wood, glass and porcelain, see further on.

PRINTING ON WOOD, CANVAS, OPAL, AND TRANSPARENCIES

_Printing on Wood._--To print on a wood block a design to be engraved on
the same presents certain difficulties. In the first place, the
sensitizing solution must not be absorbed by the wood, but remain wholly
on its surface; then the photo film, although thick enough to produce an
image sufficiently intense to be distinctly visible in all its details,
should not scale or clip away under the graver, and not interfere in any
way with the work of the artist; the least touch of the graver must reach
the wood and make its impression. Lastly, the design should be permanent.
These difficulties will be avoided by adhering to the instructions given
in the lines following.

The solution to render impervious the surface of the wood consists of

Common gelatine 5 parts
Gum arabic 3 parts
Castile soap 3 parts
Water 100 parts

Dissolve by heat on a water bath.

To apply it, the wood is rubbed with fine sandpaper, then heated over a
spirit lamp to about 86 deg. Fahr. (30 deg. C.)