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Historical Carbs and Oils
I'm just reading an article in the April issue of B&W magazine (vol 8,
#42, p.46) in which a tri-color carbro process is described. While I believe that the writer botched the description it has reminded me that I don't have a clear understanding of the differences between the carbro, carbon, and bromoil processes. I suppose that this is a tedious request for some members of this list, but if any would care to weigh in, I'd appreciate it. (I've posted this to as well.) -Lew |
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Historical Carbs and Oils
Lew wrote:
I'm just reading an article in the April issue of B&W magazine (vol 8, #42, p.46) in which a tri-color carbro process is described. While I believe that the writer botched the description it has reminded me that I don't have a clear understanding of the differences between the carbro, carbon, and bromoil processes. I suppose that this is a tedious request for some members of this list, but if any would care to weigh in, I'd appreciate it. (I've posted this to as well.) -Lew Here's the link to the alt processes faq: http://duke.usask.ca/~holtsg/photo/faq.html On that page, there are links to the processes with short descriptions, and links to references, the mailing list and the archives. It's good practice to search the archives before posting to the list. |
#3
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Historical Carbs and Oils
"Lew" wrote in message ... I'm just reading an article in the April issue of B&W magazine (vol 8, #42, p.46) in which a tri-color carbro process is described. While I believe that the writer botched the description it has reminded me that I don't have a clear understanding of the differences between the carbro, carbon, and bromoil processes. I suppose that this is a tedious request for some members of this list, but if any would care to weigh in, I'd appreciate it. (I've posted this to as well.) -Lew I also recommend the source given by Micheal Gudzinowicz. FWIW, the three color carbro process was very widely used for high quality color prints for reproduction purposes up to perhaps the late 1940's after which it was supplanted by dye transfer and Kodachrome. Carbro and and Bomoil are variations of carbon and oil process which use matrices of differentially hardened gelatin. In the Carbon process the gelatin comes in the form of a thin gelatin "tissue" containing a pigment. While actual carbon may have been used early on it is actually never found as one of the pigments. In oil printing a coating of gelatin is differentially hardened so that it absorbs varying amounts of transparent oil paint. The matrices are made from Gelatin sensitized with potassium dichromate. When exposed to strong light the dichromate hardens the gelatin in proportion to the amount of light. In carbro and bromoil another method is used to expose the sensitized gelatin. A bromide print, i.e., a normal silver gelatin print, is rolled into contact with the sensitized gelatin and left for a time. A reaction between the silver image and dichromate causes the same differential hardening effect as exposure to light. After the appropriate time the print is stripped off and the gelatin further processed as it would be for which ever printing process is being used. The advange of using a bromide print is that enlarged prints can be made from small negatives without having to make enlarged negatives for what otherwise are contact printing processes. I think the FAQ on the Alternative printing site gives much more detail. Three color Carbro was used for making prints from color separation negatives. Up to the late 1940's these were usually made from one-shot color separation cameras. The process was very fussy requiring tight control of the negative exposure and contrast and the intermediate prints. Because the hardness of the gelatin tissue was important the labs specializing in this work were referigerated. For the best quality advertising work one shot cameras, matched films or glass plates, and carbro printing materials were supplied as a system by three companies: National Photocolor and Devin-McGraw in New York, and Thomas S. Curtis in Los Angeles. The well known Autocolor materials, made in England, were not considered reliable enough for commercial work. The Kodak Dye Transfer method, while still fussy, is much less so than three color carbro. It uses silver halide emulsions which are differentially hardened by the developer. Pancromatic emulsions were supplied as well as non color sensitized ones, so that matrices could be made directly from color negatives. An improved version of this process became available in the late 1940's and, along with Kodachrome and similar multi-layer color films, completely supplanted three color carbro within a few years. Carbro and Carbon prints have the advantage of being made with pigments rather than dyes so they can have very long life (100 years plus if the pigments are chosen right). -- --- Richard Knoppow Los Angeles, CA, USA |
#4
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Historical Carbs and Oils
"Richard Knoppow" wrote in message ink.net... "Lew" wrote in message ... I'm just reading an article in the April issue of B&W magazine (vol 8, #42, p.46) in which a tri-color carbro process is described. While I believe that the writer botched the description it has reminded me that I don't have a clear understanding of the differences between the carbro, carbon, and bromoil processes. I suppose that this is a tedious request for some members of this list, but if any would care to weigh in, I'd appreciate it. (I've posted this to as well.) -Lew I also recommend the source given by Micheal Gudzinowicz. FWIW, the three color carbro process was very widely used for high quality color prints for reproduction purposes up to perhaps the late 1940's after which it was supplanted by dye transfer and Kodachrome. Carbro and and Bomoil are variations of carbon and oil process which use matrices of differentially hardened gelatin. In the Carbon process the gelatin comes in the form of a thin gelatin "tissue" containing a pigment. While actual carbon may have been used early on it is actually never found as one of the pigments. In oil printing a coating of gelatin is differentially hardened so that it absorbs varying amounts of transparent oil paint. The matrices are made from Gelatin sensitized with potassium dichromate. When exposed to strong light the dichromate hardens the gelatin in proportion to the amount of light. In carbro and bromoil another method is used to expose the sensitized gelatin. A bromide print, i.e., a normal silver gelatin print, is rolled into contact with the sensitized gelatin and left for a time. A reaction between the silver image and dichromate causes the same differential hardening effect as exposure to light. After the appropriate time the print is stripped off and the gelatin further processed as it would be for which ever printing process is being used. The advange of using a bromide print is that enlarged prints can be made from small negatives without having to make enlarged negatives for what otherwise are contact printing processes. I think the FAQ on the Alternative printing site gives much more detail. Three color Carbro was used for making prints from color separation negatives. Up to the late 1940's these were usually made from one-shot color separation cameras. The process was very fussy requiring tight control of the negative exposure and contrast and the intermediate prints. Because the hardness of the gelatin tissue was important the labs specializing in this work were referigerated. For the best quality advertising work one shot cameras, matched films or glass plates, and carbro printing materials were supplied as a system by three companies: National Photocolor and Devin-McGraw in New York, and Thomas S. Curtis in Los Angeles. The well known Autocolor materials, made in England, were not considered reliable enough for commercial work. The Kodak Dye Transfer method, while still fussy, is much less so than three color carbro. It uses silver halide emulsions which are differentially hardened by the developer. Pancromatic emulsions were supplied as well as non color sensitized ones, so that matrices could be made directly from color negatives. An improved version of this process became available in the late 1940's and, along with Kodachrome and similar multi-layer color films, completely supplanted three color carbro within a few years. Carbro and Carbon prints have the advantage of being made with pigments rather than dyes so they can have very long life (100 years plus if the pigments are chosen right). I realized after sending this that I left out some stuff I meant to include. Carbon and carbro are "developed" by washing away the unhardened gelatin in with hot water. The resulting gelatin is transferred to a final carrier sheet. For three color work there are three layers of gelatin assembled on the final carrier. Getting them in register is one of the difficult parts of the process. -- --- Richard Knoppow Los Angeles, CA, USA |
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