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.) and upon it is poured in
excess the liquefied and quite warm solution, which must be allowed to
penetrate in the pores of the wood by letting it gelatinize, when it is
wiped off clean. Nothing must remain on the surface of the wood. This
done, and while still damp, the preparation is rendered insoluble by
pouring over a solution of alum at 5 per 100 of water. The object of this
preliminary operation is to render the wood impervious, and therefore to
prevent the sensitizing solution to penetrate its texture. The wood is
then heated again and its surface whitened with a little silver white or
sulphate of barium, diffused in a small quantity of the following warm
solution:
Gelatine 1 parts
Alum 0.1 part
Water 100 parts
While wet, this is smoothed with a jeweler’s brush, taking care to leave
on the wood, a very thin layer of the mixture, only sufficient to obtain a
white surface which, by contrasting with color of the wood assists the
engraver in his work. The wood should now be allowed to dry thoroughly,
when it is coated with a tepid solution of
Isinglass 3 parts
Water 100 parts
and dried.
Now the sensitizing process differs according as whether the cliché is
positive or negative. In the former case the preparation is sensitized
with the solution employed in the black process, proceeding afterwards as
usual; in the latter, that is, when the cliché is negative, the best
process is the cuprotype.(12)
For printing, special frames are employed to permit one to examine the
progress of the impression from time to time without the possibility of
either the wood block or the cliché moving. These frames open in two.
The upper frame is provided with screws on the four sides to hold firmly
the block when it is placed into contact with the cliché by means of the
screws fixed on the cross bars. As to the cliché, if it is made on a
glass plate, it is secured on the thick glass plate of the lower frame by
two wooden bars against it pushed by screws.
When the block is ready for printing, the prepared side is usually
concave. It is straightened by slightly wetting the back and resting it
on one end, prepared side against the wall.
_Printing on Canvas.—_The canvas should be first brushed with a solution
of aqueous ammonia in alcohol, 1:3, to remove greasiness until the thread
just commences to show, then, when rinsed and dry, rubbed with fine sand
to give a tooth, dusted, washed with a sponge and then coated with the
following solution, proceeding afterwards as in the cuprotype process:
Isinglass 8 parts
Uranic nitrate 5 parts
Copper nitrate 2 parts
Water 200 parts
_Printing on Opal, Celluloid, etc._, is quite simple; it suffices to coat
the material with the following gelatine solution, and, when the film is
dry, to proceed in operating by any one of the processes before described.
The sensitizing compound may be incorporated to the gelatine solution, but
we prefer not to do it and to sensitize the plates as they are wanted for
use.
A. Gelatine 4 parts
Water 70 parts in volume
Dissolve and mix little by little in order:
B. Chrome alum 0.25 parts
Water, hot 20 parts
C. Alcohol 10 parts
When coated place the plates on a level stand until the gelatine is set,
and let them dry on a rack.
_Transparencies._—Prepare the plate as directed above with
A. Gelatine 6 parts
Water 70 parts
B. Chrome alum 0.3 part
Water, hot 20 parts
C. Alcohol 10 parts
Sensitize with the uranic-copper solution employed in the cuprotype. By
this process transparencies of a rich brown, not actinic, color are
obtained. Consequently they can be used to reproduce negatives by the
same process. For lantern slides they may be toned black by platinic
chloride.
To strip off the picture, apply, first, on the glass plate a substratum of
India rubber, 2 to 100 of benzole, coat with plain collodion, immerse the
plate in water as soon as the film is set, and when greasiness has
disappeared pour on the gelatine solution and proceed.
For tranferring on any material, a sheet of paper is immersed in a
solution of India rubber cement in 20 parts of benzole, dried, coated with
the gelatine solution, sensitized, etc., by operating in the ordinary
manner. After development, the proof, being dry, is brushed over with
alumed gelatine moderately warm, dried, immersed in tepid water until the
gelatine is softened and tacky, when it is placed on the material and
squeezed into contact. This done, the transfer should be allowed to dry
thoroughly. Now, by imbuing the proof with benzole to dissolve the India
rubber, the paper is easily stripped off, leaving behind the picture
adhering to the material.