(top row from left to right) Museum no. PH.346-1980, PH.342-1980, PH.341-1980
(bottom row from left to right) Museum no. PH.332-1980, PH.338-1980, PH.345-1980
Carbon printing was most popular between 1870 and 1910 but is still sometimes used today. These images are an example of the technique.
Although patented in 1855 by Alphonse Louis Poitevin (1819-82) and improved in 1858 by John Pouncy (1818-94), carbon prints only became fully practicable in 1864, with the patented process and printing papers of Joseph Wilson Swan (1828-1914).
The prints show dense, rich, glossy tones that are either black or a deep brown in colour. Various pigments could be used to give access to a greater range of colours and the prints show slight relief contours (thickest in the darkest areas) as a result of the process used. The most important feature of a carbon print is its permanence; it contains no silver impurities that can deteriorate.
The main principle of the process is the fact that gelatin (to which potassium bichromate has been added) becomes insoluble when exposed to light, in proportion to the amount of light received. A sheet of lightweight paper was coated with gelatin containing potassium bichromate and a pigment.
In daylight this tissue was placed under and in contact with a negative. This exposure was timed, as the dark-coloured paper did not show an emerging image. Those parts of the gelatin that were exposed to light through the negative hardened.
In order to wash away the unhardened gelatin and reveal the image, the face of the exposed carbon tissue was squeezed in contact with a second sheet of paper coated with an insoluble gelatin layer, thus forming a sort of gelatin sandwich which was then soaked in warm water. The paper floated free and the unhardened gelatin was washed away, leaving the image attached to the second sheet. The sheet was then immersed in water containing alum (which) hardened the remaining gelatin and removed any yellowish bichromate stains. Gordon Baldwin, 'Looking at Photographs', J. Paul Getty Museum, 1991
John Thomson (woodburytypes - a photomechanical version of carbon printing)
This photograph can be found in Print Room Box 12.