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.

2

Prepare Gun Cotton

Add the ingredients

"Take five and a half ounces of nitrate of potash in powder and add to it in a convenient size bowl ten ounces, by weight, of common commercial sulphuric acid"

"Stir the whole with a glass rod, and introduce as much finely-carded cotton, about two drachms, as will absorb the mixture and be at the same time thoroughly charged with it."

Put a cover on the vessel, and allow the action to go on for five minutes.  Then remove the cover, and with a glass rod, poke and separate the fibres of the cotton"

The Result

"If the action be too intense, which is known by the extreme heat of the surface of the vessel, moderate it by applying a cloth soaked in cold water to its external surface."

"Then let the cotton be plunged into cold water, and washed so thoroughly that not the slightest trace of acid can be detected.  It should then be dried at a very low temperature, and put past in a bottle for use."