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  1. #1

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    Gum-Silver Process

    Gum-silver Process

    Adapted from an entry in the Scientific American Cyclopedia of Formulas, 1932

    Solution No. 1 : Dissolve 50 grams of gum Arabic powder in 100 mLs of water. Gum Arabic does not dissolve quickly, but it will dissolve, so have the gum sit in the water over night. The next day it should be completely dissolved. If you already have a commercially prepared gum Arabic solution intended for gum printing, I would suggest you start with this and see how it works.

    Solution No.2 : Add 6 mLs of glacial acetic acid to 10 grams of Solution No.1. This will be solution No. 2. Some of the gum Arabic will crystallize out when the acetic acid is added, but stirring will bring most of it back into solution.

    Solution No.3 : Dissolve 2.2 grams of silver nitrate in 10 mLs of distilled water. Add this with stirring to Solution No.2, and this will be solution No.3. Stirring this solution will dissolve any undissolved gum Arabic.

    Coating the paper : Under a red safelight I use a foam brush to apply the gum-silver to the paper . I let the paper dry in the dark.

    The negative : Like salt printing, you need a very high contrast negative. I tried to increase the contrast by adding 1 drop of 5% potassium dichromate solution to the gum-silver solution prior to coating the paper. The increase in contrast was very slight, and approximately 50% more exposure was needed. One positive result was that the image tone shifted from an orange/red color without the dichromate to a nice warm sepia color with the dichromate. This result might be due to the addition of the dichromate, and/or to the paper used. The article says that the image color depends upon the paper used.

    Printing : The image appears during exposure. I expose until the image is a bit more darker than what I would want in the finished print.

    Processing : After exposure wash the paper with tap water. The unexposed silver nitrate will turn the wash water a milky white. Continue washing with changes of water until the water is clear. Then fix with a 2% sodium thiosulfate solution for about 10 minutes.. Wash the print again to remove the fixer. The print will lighten slightly during the washing and fixing.

    Toning : If you wish to tone with gold and/or platinum you should tone before fixing. I did not try toning with gold or platinum, but for the sake of completeness, and to satisfy my curiosity, I did try selenium toning. A toning solution containing 5 mLs of KRST added to 1 liter of water ruined the print in 2 minutes. The print was noticeably bleached, and the color was changed to an ugly slate gray.

    For my traditional black and white printing I use Kodak’s T-55 selenium toner, which you have to prepare yourself, and which does not contain any thiosulfates, which I feel are responsible for the rapid bleaching of salt prints with KRST. I added 5 mLs of this to a liter of water and immersed a print in this. After 2 minutes the tone of the color shifted slightly from the warm sepia color to a slightly more yellow sepia color, and after 5 minutes the print started to bleach. I doubt if the 2 minutes in the very dilute T-55 toner added any protection to the silver in the print.

  2. #2
    Steve Smith's Avatar
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    Does this need UV light exposure or will it work with visible light?


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  3. #3
    Jim Noel's Avatar
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    T here was a period when people did a lot of experimenting with processes. This was especially true during the depression when photographers tried many ways to reduce costs so they could keep working. This is one of many variations on gum bichromate printing from that era. It most likely does need UV to harden the gum or it will wash off the paper.
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  4. #4

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    Steve - yes, you need a UV source of light.

    Jim - I see this as being more closely related to salt printing rather than to gum bichromate printing. In both salt printing and gum-silver, the image is formed by the interaction of the light on silver chloride (salt printing) or silver nitrate(gum-silver). In gum bichromate, the light interacts with the gum, hardening it in direct proportion to the amount of light falling on it, which is related to the different densities in the negative. The pigment dissolved in the gum provides the image, but it is the gum that reacts to the light.

  5. #5

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    Do you mix all 3 in the end to produce: 100mL gum arabic + 6mL acetic acid + 10mL silver nitrate 22%? Or are you just coating what you're referring to as Solution #3: 20mL gum arabic + 6mL acetic acid + 10mL silver nitrate 22%?

  6. #6

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    Quote Originally Posted by tinyfailures View Post
    Do you mix all 3 in the end to produce: 100mL gum arabic + 6mL acetic acid + 10mL silver nitrate 22%? Or are you just coating what you're referring to as Solution #3: 20mL gum arabic + 6mL acetic acid + 10mL silver nitrate 22%?
    You take 10 grams of the gum arabic solution and add 6 mLs of glacial acetic acid to it. Set this aside. Then dissolve 2.2 grams of silver nitrate in 10 mLs of distiller water. After the silver nitrate has dissolved, add this to the gum arabic solution you have set aside. You end up with a solution containing 10 grams of gum arabic solution, 6 mLs of glacial acetic acid, 2.2 grams of silver nitrate, and 10 mLs of water, all mixed together. You don't mix everything together at once, since I doubt if you'll get everything into solution. The order of mixing is important.

    Hope this helps.

  7. #7

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    Thanks for the clarification. Given what I have access to, I'll experiment with 20 mL gum arabic (I only have it as a mixed liquid), 6mL undiluted stop bath (which is basically vinegar), and the silver, then expose it for about the same time as a Van Dyke.



 

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