The Wet Collodion Process

Thomas Rodger

Below are some extracts from Thomas Rodger's paper On Collodion Calotype,
 read to the Royal Scottish Society of Arts in Edinburgh in February 1854.

7

Fix the Plate

Fix and Wash

"The development  being now completed, the picture must be thoroughly washed, by pouring a stream of water over it; and then it must be secured from the further action of light" [fixed] "and rendered more fit for transferring if a negative, by removing the yellow iodide of silver from the blanks and shadows of the picture."

For this purpose I use:

            -  Cyanide of potassium (crude cakes), 120 grains

            -  Water (common), 8 ounces.  Dissolve."

"After allowing this solution to remove the whole of the spare iodide of silver, the picture is again submitted to a thorough washing, and allowed to dry spontaneously, by a gentle heat."

Varnish

"As the collodion is liable to be scratched by the paper or otherwise in copying, it is better to be coated with varnish to prevent this, especially if it is to be frequently copied. 

The varnish used for this purpose is comprised of -

            -  Gum damar 1.5 or 2 drams.

            -  Mineral naphtha, 4 ounces."

Intensify (if necessary)

"After the picture has been fixed, and CAREFULLY washed, from  cyanide of potassium, I pour over it a quantity of the negative developing solution, diluted with an equal bulk of water."

"Upon this is poured a quantity of a solution of nitrate of silver, in the proportion of 15 grains to 1 ounce of water, and I continue to keep the plate in motion for a time."

"If the image is made strong enough by a single applicaton, it is well;  but if not, a little more nitrate solution and developing liquid should be applied till the desired pitch is obtained."

"After this, the plate must be well washed, and again submitted for an instant to the cyanide of potassium, and finally washed  thoroughly."