'Portrait of Three Unidentified Girls'
Museum no. E.1163-1992
Collodion positive was invented by F. Scott Archer in 1822 and was in widespread use by the mid 1850s. It is also sometimes called an ambrotype.
This portrait can be identified as a collodion positive because the image is always shown as a positive unlike the daguerreotype where both the positive and negative images are visible depending on the lighting of the object.
A sheet of glass was hand-coated with a thin film of collodion (guncotton disolved in ether) containing potassium iodide, and was sensitised to the light with silver nitrate to create a collodion negative. The back is painted black or covered with a piece of black cardboard or cloth in order to achieve the effect of a positive image.
This photograph can be found in Print Room Box 12a.