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!
Originally Posted by htmlguru4242
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