The pictures prepared for projection by the magic lantern are made
on glass of one size, invariably 3-1/4×4 inches, and are copies of
negatives made by transmitted light and by two methods. When the
negative is made by the detective, or pocket cameras and on plates
3-1/4×4-1/4, the positives or slides may be made by contact
printing; that is, the prepared plate is placed in contact with the
negative, film sides together or touching in a printing frame, the
back pressed closely down and the plate exposed to the light of a
gas or lamp flame--daylight is too strong--for from five to ten
seconds, according to the density of the negative; the plate is then
developed perfectly with ferrous oxalate until the picture is seen
clearly on the surface; when the shadows have become sufficiently
dense, or before there is any discoloration of the high lights,
remove and wash and fix in hypo and alum. (See Roche's formula
[p201] in article on Transparencies.) Remember that all parts of the
pictures that represent the whites should be clear glass.
When the negative is larger than the slide, then the copy must be
made in the Camera. (See article on transparencies.)
It is claimed by some that slides made by the collodion process are
superior to those made on dry plates, but in my own personal
experience I have found Anthony's transparency dry plates superior
to all others and better than collodion.
To protect the film surface of the slide, thin, clear glass of a
corresponding size is placed against the film surface with a paper
mat (the opening of which should closely correspond with the outline
of the picture) between, and the two bound together neatly with
adhesive paper.