ed to a certain shade, or
when the one next by commences to appear or is faintly printed, etc., the
exposure of the tissue is sufficient. This, as the reader has already
inferred, is a matter of experience, the guide being the knowledge of the
intensity negative tested as above explained.

_Development.--_The carbon prints are developed either on a sheet of paper
upon which it should remain (single or simple transfer), or on a provisory
support to be afterwards transferred on paper or any other material
(double transfer).

_Simple Transfer.--_This process is quite simple: The impressed tissue and
a sheet of paper coated with alumed (insoluble) gelatine are immersed face
to face in cold water, and when the tissue is softened both are removed,
one superposed on the other, and the whole, being placed on a glass plate
and covered with a thin oil cloth, is firmly pressed into contact with the
squeegee. The rationale of applying under water the tissue on the
gelatinized paper is to avoid the interposition of air bubbles.

To operate by simple transfer the tissue should be impressed under a
reversed negative. The reason is obvious.

_Double Transfer.--_By this method the carbon prints are generally
developed on porcelain or opal plates, which more easily than glass plates
permit one to follow the progress of the development and to retouch the
imperfections before transferring the picture on paper.

In order that the image does not adhere on the provisory support a little
of the following mixture is spread over the plate, which is then pretty
strongly heated, and, when it has cooled down, polished lightly with a
piece of white flannel to obtain a very thin and even layer free from
striae. If the plate has not been used before for the purpose in question,
it should be waxed a second time in the same manner:

Yellow wax 4 parts
Rosin 1 part
Turpentine or benzine 250 parts

The plates can be developed on the plates so waxed, but for "full gloss,"
that is, for enameled pictures, a film of collodion is applied on the
plates, which then, instead of being waxed, should to be simply flowed
with a solution of India rubber 1 to 100 of benzole:

Ether 250 parts
Alcohol 250 parts
Castor oil 1 part
Pyroxyline 5 to 6 parts

When the plate is coated and the collodion film set, it is immersed in
water until greasiness has disappeared and wanted for use. Then the
tissue, previou