The solvent most generally used for fixing or clearing positives is
cyanide of potassium.
By the term "fixing" is meant the dissolving from the collodion film
all the iodide of silver not acted on by the developer; the
remaining portion of the silver is in a metallic state and
constitutes the image; the cyanide very readily dissolves the
iodide, but acts very slowly on the metallic silver.
This fixing solution should be contained in a glass upright dish,
enclosed in a wood case, with a tight or close-fitting cover, this
in order that as little exposure to the air as possible may be had,
as the fumes [p021] arising from the evaporation of the solution
are injurious.
Two ounces of cyanide to 64 ounces of water will make a suitable
fixing solution for plate pictures; if, however, its action is
thought to be too slow, add more.
The plate picture having now been developed and fixed, it only
remains that it should be dried, varnished, cut into shape, placed
in the proper envelopes and it is ready for delivery.
Those desiring more extended instructions in the making of plate
pictures are referred to the work on that subject, entitled, "The
Ferrotype and How to Make it," published by E. & H. T. Anthony &
Co., of New York.