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.

8

Prepare the Paper

Select a Paper

"Various kinds of paper are suitable for obtaining copies.  I use almost exclusively a paper manufactured by Pirie and Sons."

"No. 3 is on a cream-coloured wove paper, made by Cowan of Edinburgh.  No. 1 is on Turner's photographic paper, procured from W & J Milne, Hanover Street, Edinburgh."

[William & John Milne had a business at 33 Hanover Street.  They were listed in the Edinburgh & Leith Post Office Directories, 1854-55 (and other years) as: "Booksellers, desk and dressing case makers".]

Coat the Paper

"Having got the paper fit for the purpose, the first thing to be done , before applying the blackening agent, is to imbue it with  some of the metallic chlorides."

"A solution of one salt may be used, or a combination of two or more.  I use a mixture of two  chlorides  -  viz. terchloride of gold and chloride of sodium, of the following strength:

            -  Chloride of sodium, 50 grains.

            -  Solution terchloride of gold, 30 drops.

            -  Rain water (pure), 20 ounces.

The strength of the solution  of terchloride of gold is 15 grains of the crystallized chloride to 4 drams of distilled water."

"The solution being put into a shallow dish of a size suitable fro the sheets of paper, they are taken one at a time by two adjacent corners, and are slowly drawn through the solution, fires one way then the other.  They are then pinned by one corner on a wooden screen to dry."

Render the paper Sensitive to Light

"Taking a piece of the paper, and driving off any dampness it may have contracted by slightly warming it, I then proceed, with a glass rod or a pellet of cotton, to coat its surface with ammonio-nitrate of silver as evenly as possible, and then dry it quickly by holding it to the fire or pinning it up in a dry, darkish place."

"It is advisable to use the sheet as soon as possible after it has been prepared."