Thursday, February 11, 2010

19th century photo processes





1./2. Salt Prints
3. Collodion Print
4. Carbon Print
Salt Print: is a positive printing process invented by William Henry Fox Talbot.
Process: the negative is placed on a sheet of paper, that has been previously soaking in salt water and coated in silver nitrate. After, the negative and contact paper are exposed to sun, or put in the Nova Exposure Unit (in our case). The print is then fixed in hypoclear, then washed and dried.
Notes: 1) the image is embedded into the fibers of the paper, giving it a matte look.
2) The image can range in colors of brown.

Carbon Prints: the negative is printed onto tissue containing carbon and other gelatin-based pigments. The gelatin is made light sensitive by a bath of potassium bichromate, before the negative is exposed to the tissue. After washing the tissue, the image is transferred to a paper base and the backside of the tissue is striped off. This process was patented by Joseph Wilson Swan.
Notes: 1) prints can have a wide tonal range.

Collodion Prints: Sticky nitrocelluluse emulsion collodion (?) is mixed with silver chloride and coated on paper, giving the surface a variety of different effects such as matte, glossy, or semi-glossy, similar to an albumen print. The beauty of collodion prints lies within the sharpness of the white of the image, that the albumen print lacks.
Note: I will probably not attempt this, as it makes no sense to me.