annot be made in the ordinary manner on account of the impossibility
to eliminate entirely the chromic salt which tinges the material yellow.
To turn the difficulty, it suffices to wash off in several changes of cold
water all the unaltered bichromate from the prints on their removal from
the printing frame, and to proceed as usual, or the prints can be allowed
to dry and transferred at some future time.

Canvas should be prepared by brushing with a solution of aqueous ammonia
in alcohol, 5:20, to remove greasiness until the thread is apparent, and,
when dry, rubbed with sand to grain it--or to give a tooth, as it is
termed--then rubbed dry with a solution of soluble glass, 1 to 10 of
beer.(32)

Palettes should be rendered impervious, or nearly so, by flowing upon them
a solution of alumed gelatine, which is allowed to penetrate into the
pores of the wood and the excess scraped off when solidified, when the
surface may be whitened, if necessary, as for printing on wood box, q.v.

Opals, porcelain, or ivory should be prepared with the following
substratum:

Gelatine 50 parts
Water 400 parts
Chrome alum, 4:100 6 parts

Very fine carbon proofs having the appearance of pictures on opal plates
are made by transferring in the following manner, devised by the author:

Develop on the ground surface of a glass or porcelain plate, well waxed,
to obtain a matt picture, or in the ordinary manner for "full gloss," and
when the image is retouched or colored, apply a thin coating of gelatine,
let dry and coat with the following opaque collodion:

A. Ether, conc. 100 parts
Alcohol, 95 deg 90 parts
Pyroxyline 7 parts
B. White zinc in very 9 parts
fine powder
Castor oil 3 parts
Alcohol 10 parts

Grind in a mortar, adding ultramarine blue and carmine, or a little of any
suitable coloring matters, and mix to A. When the collodion is dry, which
requires a few hours, strip the whole or back with strong white or colored
paper before stripping. A solution of gelatine with glycerine, white zinc,
etc., may be substituted for collodion when the pictures are employed as
ornaments on wood, etc. Carbon prints on celluloid are now made for
similar purposes.
OPAL GELATINE SOLUTION
Gelatine 150 parts
Glycerine 15 parts
Zinc, white 40 parts
Water 600 parts

To which some coloring matters may be added according to