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.

3

Prepare Collodion

Mix the ingredients

"Take a sulphuric ether 12 ounces;  add to it half an ounce of iodide of potassium, previously dried and bruised in a mortar, and allow it to become saturated by shaking;  then add 6 grains of iodide of silver, shake again to dissolve this, and, after it has become clear, pour it off into another bottle."

"Next, add about 72 grains of soluble or gun cotton, or, what is better, add as much soluble cotton as you consider sufficient to make a solution so thin as to pour freely over a plate of glass."

"Then in 12 drams of alcohol dissolve 10 grains of bromide of potassium, and after it is entirely dissolved, add as much iodide of potassium as will saturate the spirit.  The whole of this is to be added to the above solution of gun-cotton in sulphuric acid and well shaken."

"As I have found a minute quantity of free iodide to be useful in collodion, 2 grains of it  may be added to the above quantity."

Use for Negatives of Positives

"The preparation now described is especially adapted for negatives.  But for glass positives, it also suits exceedingly well."

(Note:  glass positives are Ambrotypes.)