Historical Carbs and Oils

Discussion in 'Darkroom Developing and Printing' started by Lew, Feb 24, 2006.

  1. Lew

    Lew Guest

    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, Feb 24, 2006
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  2. Here's the link to the alt processes faq:


    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.
    Michael Gudzinowicz, Feb 24, 2006
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  3. 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, Feb 24, 2006
  4. 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, Feb 25, 2006
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