_Ready Mode of iodizing Paper._--The readiest way I have found of iodizing
the beautiful paper of Canson Frères, is the cyano-iodide of silver, made
as follows: Twenty grains of nitrate of silver may be placed in half an
ounce of distilled water, and half an ounce of solution of iodide of
potassa, fifty grains to the ounce, added to the silver solution. Cyanide
of potassa may then be added, drop by drop, till the precipitate is
dissolved, and the whole filled up with four ounces of water. This solution
requires but a very few minutes' floating upon water containing a small
quantity of sulphuric acid; and it is then ready, after a bath of nitrate
of silver, for the camera, and will not present any of the disagreeable
spots so noticed by most photographers. This paper is probably the best for
negative pictures we have at present; although, if very transparent paper
is required, oiled paper may be used for negative pictures very
successfully; or paper varnished is equally good. The oiled paper may be
prepared as follows: Take the best walnut oil, that oil having less
tendency to darken paper of any other kind, and oil it thoroughly. It must
then be hung up in the light for a few days, the longer the better, till
quite dry. It may then be iodized with the ammonio-nitrate, the ammoniated
solution passing more readily over greased surfaces. The varnished paper
may be prepared by half an ounce of mastic varnish and three ounces of
spirits of turpentine, hung up to dry, and treated as the oiled paper in
iodizing; but both are better for resting a short time previous to iodizing
upon water containing a little isinglass in solution, but used very
sparingly.
As I have experienced the excellence of these preparations, I hope they may
be useful to your photographic students.