-Collodion was discovered in 1846, and is made by dissolving pyroxylin in a mixture of ethanol (alcohol) and ether.
-Pyroxylin is made by treating cotton with a mixture of nitric and sulphuric acid under carefully controlled conditions and had been discovered a few years earlier.
-Guncotton is made in the same way as pyroxyline, but with a longer acid treatment and is dangerously explosive
-Collodion is not light sensitive, but is coated on a sheet of glass to act as a transparent support for the light sensitive compounds.
The camera needs to be set up and focussed ready to take the picture immediately the plate is ready.
1. Collodion is mixed with an 'iodiser', which contains bromides and iodides dissolved in alcohol.
2. A glass plate is carefully cleaned and either edged with rubber solution or coated with an albumen substratum layer
3. A pool of the mixed collodion is poured onto the plate, which is tilted to spread it evenly, and excess is poured off.
4. When some ether and alcohol has evaporated and the surface is tacky, the plate is put into a solution of silver nitrate in water for 2-3 minutes. This stage produces light-sensitive silver halides.
5. The plate is drained and quickly put into the plate holder
6. The exposure must be made before the plate dries out (about 10 minutes.)
7. Exposure times in good light were typically around 1 -10 seconds at f11
8. Developer solution (usually acidified ferrous sulphate or pyrogallol) was poured onto the plate and tilted to cover it evenly and kept moving until development was complete - usually several minutes
9. The plate was briefly rinsed with water
10. It was fixed using a bath of potassium cyanide (poisonous) or sodium hyposulphite
11. It was washed for a couple of minutes (longer if hypo was used)
12. Often plates were intensified, most commonly using a mixture of developer and silver nitrate, although lead or mercury intensifiers were also used.
13. Plates were then dried, usually over a spirit lamp
14. The plate was heated gently over a spirit burner and a varnish was then poured onto the collodion and flowed across to give an even coat. When this had set the plate was ready for printing