 Anna M. Bebee |
Acid Cross Processing I was just looking through all of the recent entries and saw a photo where the photographer said she did "acid cross processing." I have never heard of this, what is it? The photo was really cool looking and I was just curious.
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W. |
Hi Anna, The lady may have been referring to a fancy way of chemical processing of silver bromide film. Have fun!
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Alan N. Marcus |
Cross Processing: The most common color films in use today are process C-41 color negative and process E-6 color transparency. Both containing unexposed silver salts as this technology is based on the black & white expertise. Both are known as an incorporated material meaning dyes are infused during manufacture however they are in a luco state meaning hidden. After the camera exposure, they are chemically developed. During development both will yield a negative black & white silver image. In the case of the C-41 process, the dyes are caused to blossom simultaneous with the generation of the negative silver image as the developer combines both a color and a black & white developer. The E-6 process is more complex. A first developer bath generates a short-term negative silver image ensuing from those silver salts that were exposed in the camera. The silver salts comprising this negative image are reduced to metallic silver and are no longer light sensitive. During this fist developer the incorporated dyes are unaffected and remain in luco state. Next the film will be chemically fogged. This renders developable those silver salts that were not camera exposed. These silver salts when developed yield a positive silver image. To accomplish, the film is immersed in a black & white developer solution commingled with a color developer. This second developing yields a positive silver image and positive color dye image. Both film types now have brilliant color but the colors are veiled as they are superimposed on silver images. Next the film is chemical bleached to remove the silver. Bleaching is a misnomer; actually the silver images are chemically converted back to a silver salt as the next step known as fixing is a solvent for silver salts. Thus all silver is washed away revealing the beautiful color image. Photo labs are run by humans and errors occur. C-41 is mistakenly processed in E-6 and visa versa. Also both might be accidentally processed in black & white chemistry. Once mal-processing occurs the desperate lab technical schemes of ways to salvage. If a silver image is present it is possible to subject the film to a bleach solution. This generates silver salts that can be re-develop in a color developer solution. These salvage procedures produce substandard images but anything is better than nothing. As always people see benefit from such method such as increased ISO or the fabrication of eccentric colors for artistic purposes. Thus intentional cross processing. The first step in cross processing is bleaching. Today the most common bleach solution is EDTA. This is an acid crystalline also used to prevent separation in bottled salad dressings (check the label). As a side-bar from an earlier time: Safari photography to the jungle or desert presented a problem as to how to preserve exposed color film which deteriorates rapidly when subjected to high heat and humidity. A valid technique was to develop color film in the field using black and white chemicals this arrested latent image shifting. . Returning to the lab, the film was beached and the re-developed in a color developer. Alan Marcus
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William Schuette |
Bill
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