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  1. #1
    htmlguru4242's Avatar
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    Isolation of Tannic Acid from bark

    I know that tannic acid / gallic acid developers were used the past for developing film (pyrogallol is, obviously, still used today).

    Does anyone know how to isolate tannic acid from the bark / nutgalls of oak trees? I have a lot of oak trees around and gallic and tannic acids are expensive to purchase commercially ...

    Any ideas how to do this?

  2. #2
    noseoil's Avatar
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    I wouldn't try to re-invent the wheel. Once you have isolated the tannin, you still have to come up with a formula to work with it in a developer. Photographer's formulary sells PMK pyro kits, or for that matter, pyrocat, both of which are superior developers.

    Seems to me you would be spending more time in rendering the oak galls than in taking pctures and developing them. Why set up a lab when the finished product is in no danger of going away commercially? tim

  3. #3
    htmlguru4242's Avatar
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    I see what you mean here, though I think that it would be a neat exercise; I live playing around with chemistry, to me, it's an interesting process to make developers.

  4. #4
    Photo Engineer's Avatar
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    Dry acorns, grind them and boil in water. Save the water and filter out the solids.

    The water can be concentrated by gentle heating to get tanins.

    PE

  5. #5
    htmlguru4242's Avatar
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    Ah, thank you, PE, I'll try that, though I didn't realize that it was so simple ...

    What should I be looking for as far as a basic formula for a develoepr after this?

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    Donald Qualls's Avatar
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    I'd start with one of the old gallic acid formulae from the 1870s-1880s. Google for developers for use on dry plates, you should find what you want. What you get by evaporating acorn tea will be of low purity relative to gallic acid, so you'll probably have to use a good bit more of it than those formulae call out.

    BTW, you can also extract tannins from black tea, though I don't know if the yield is high enough to be worth paying for the tea (even at only a couple cents a bag) compared to picking up acorns in the park (or your front yard).
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  7. #7
    Photo Engineer's Avatar
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    BTW, that reminds me.

    The acorns, once boiled free of tannins can be dried, shelled and ground to make a flour for breads and cakes that is supposedly quite tasty. At least the Native Americans thought that to be so.

    They served it with venison stewed in maple syrup. At least that is according to one menu that I read years ago. Spices included 'greenstick' or sassafrass.

    PE

  8. #8

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    You can also leach tannic acid directly from the leaves of oak trees. Take a wooden barrel, fill with leaves, and acorns and pour boiling water over the leaves. Let the it steep for a week or so and decant. Boil down gently with good ventilation) for higher concentration of acid.

    The tip about the eating the acorns are true; you can make some interesting pancakes from acorn flower and they are good to munch on after 3 changes of boiling water and "candied" with melted sugar.

  9. #9

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    Quote Originally Posted by htmlguru4242
    Ah, thank you, PE, I'll try that, though I didn't realize that it was so simple ...

    What should I be looking for as far as a basic formula for a develoepr after this?
    Are you trying to make pyrogallic acid from the tannins? If so, you need to first fermant the oak galls and let them mold, and then extract them with water saturated ether and then carefully dry the extract. It's very flammable!

    Heat the tannin extract with either strong acid or base to make gallic acid. Then you need to heat the gallic acid with 3 times its weight of water in an autoclave to make pyrogallic acid. (According to my Hawley's Condensed Chemical Dictionary.)

    Actually, I've seen an online reference to an old photo manual from around the 1880s that has really nice descriptions of how to prepare chemicals like this from basic materials. Perhaps someone else here knows the reference and can link to it for us?

    If you are looking for tannic acid, it is actually realatively cheap commercially. 100g for $30 at Photographers Formulary, and 1 lb for $49 at Artcraft Chemicals.

    Anyway, I've played around with using tannic acid as a developer - at least a couple of tries to see how feasable it is. It works. It actually stains pretty nicely too. Visually (and that's all the further I've taken it) it's similar to Pyrocat HD. I can't find my notes at this point, but try substituting tannic acid for pyrocatechol in the Pyrocat formula, but use 5 or 10 times more tannic acid for a start. Using a formula like this, I processed some FP4+ for 10 minutes by tray at about 25C and I got a visual CI of 0.66 and a blue CI of 0.73. The base+fog was nice and low - 0.11 and 0.12 respectively.

    So it does work. I was intruiged by the idea that tannic acids, while similar to pyrogallol and pyrocatechol, are a much larger molecule. THat should have an affect on a couple of different areas that I could think of. Safety and the physical action of the developer.

    Tannic acid is not one specific compound, but rather, a mixture of very closely related compounds. They usually have a molecular weight of around 2000 AMU and it is often given a molecular formula of C76H52O46. Or I should say group of molecules. They used to be classed as glucosides as they have sugars that hold the componants of the tannins together via esters, but nowadays they are considered a class of chemicals on their own right - tannins are now classed as a polyphenolic compound. And that is what related them to compounds used in "pyro"-type staining developers. Think of the biggest, hairyist molecule you could make by linking together dozens of pyrocatechol and pyrogallol molecules, with all the -OH functional groups hanging out into space to do their magic on all your AgX crystals in the film. And even though it is such a large molecule, tannic acid is very soluble in water, so making the developer is not going to be an issue. (One thing I've noticed is that tannic acid usually dissolves incompletely - even though it is very soluble in water, there are still some dregs left behind - about 1% maybe. I suggest you filter the solution before you actually try using it on some non-test images.)

    The other thing I thought interesting was that if the molecular size of tannic acid is so large, then that may help make it a "safer" staining developer. It should be less absorbed by your skin. And the MSDS data bears this suspicion out.

    While tannic acid has a Health Rating of "2 - Moderate", it actually has a Contact Rating of "1 - Slight" and is said to be only a "Mild Irritant". It is neither a known or anticipated carcinogen. See: http://www.jtbaker.com/msds/englishhtml/t0065.htm

    Compare this with pyrogallol having both a Health and Contact Rating of "2 - Moderate" and it is listed as a skin "Irritant". See: http://www.jtbaker.com/msds/englishhtml/P7973.htm

    Pyrocatechol is has a Health and Contact Rating of "3 - Severe", and is listed as "Corrosive" under Skin Contact. See: http://www.jtbaker.com/msds/englishhtml/P7896.htm

    Of course, those listing are for the dry powders, but these properties will probably be reflected the these compounds while in solution.

    So tannic acid is significantly less hazardous by skin contact. And I know we all try to use gloves when handling our developers these days, I'm sure there are still some people out there that use bare skin when developing by tray. So I was thinking that a tannic acid developer would greatly reduce the risks associated with this practise. (Tannic acid also has a lower Oral LD50 than either pyrogallol or pyrocatechin, but this advantage may be lost by having to use more of it in the developer since tannic acid seems from my few tests to be a little less active.)

    And the last thing I thought interesting about trying a tannic acid based developer is that it may not penetrate very deeply into the emulsion - as I said, it is considered to have a molecular weigth of around 2000 AMU. That's huge compared to most other developer compounds. It seems to me that it will inhibit transport deep into the emulsion. And I'm guessing it will bind to the gelatin in the emulsion with all those -OH functional groups hanging off of it. I suppose that's why James and Mees list tannic acid as one of the strongest staining developer agents (ahead of pyrocatechol but behind pyrogallol), so that seems like an another reason to try this.

    Anyway - I would skip ahead from making some tannic acid and buying some for yourself and try a few developer fomulas with it. I think it holds a lot of promise, both from a staining viewpoint, as well as a safety one as well.

    For something simple, try a PMK based formula but with 5 times more tannic acid than pyrogallol for starters.

    Let me know what you find!

    Kirk - www.keyesphoto.com

  10. #10
    Donald Qualls's Avatar
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    Quote Originally Posted by Kirk Keyes
    If you are looking for tannic acid, it is actually realatively cheap commercially. 100g for $30 at Photographers Formulary, and 1 lb for $49 at Artcraft Chemicals.
    Ummm. Your definition of cheap doesn't match mine, or likely that of htmlguru either (he's in college, last I checked). Formulary has Metol for about 1/4 that price (a pound is barely more than 100 g of tannic acid), which IMO doesn't put tannic acid in the "cheap" category. The Artcraft price is closer to reasonable, and there are probably other suppliers who can beat that.

    And I suspect part of the idea here is related to the "making photo chemicals from common materials" meme -- making developer from acorns has a lot more cachet, even if the resulting developer is inconsistent, than making it from technical grade tannic acid that arrives in a plastic bottle. Heck, I've got enough acorns in the yard that this tempts me (though I might have missed out for this season, since the squirrels have probably long since collected the good ones).

    BTW, you can extract tannins from oak bark, too, just as from the leaves. There are manys streams in the northeastern United States that look like tea as they flow in their beds, due to tannins picked up from oak roots and leaves. I'm guessing those aren't popular to drink from...
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

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