Got Tannic Acid, can I make pyrogallol from it?

[ZorkiKat]

...or is this not possible? Got about 300 grammes of the stuff left over from a leather tanning project.

 

[Aggie]

quick answer....No

 

[PhotoJim]

You need gallic acid to make pyrogallol (which is also known as pyrogallic acid).

Since pyrogallol is somewhat dangerous to handle, it's far safer to buy it, even if you could theoretically make it.

 

[philldresser]

ZorkiKat

If you can't find a use for it then send me some in the post so I can tone my cyanotypes Doh! , now I've told you what you can use it for.

Phill

 

[Kirk Keyes]

...or is this not possible?

But you can make a staining developer out of it. I've played with it just a little - try taking Pyrocat-HD formula, and substitute 10x as much tannic acid as the amount of pyrocatechol in the forumula. It works, and it should actually be a safer developer since the tannic acid is much less hazardous than pyrocatechol.

There's another thread on APUG where I think I posted more info on this.

 

[Donald Qualls]

Or, since you can't get metol, phenidone, etc. where you are, you might make a variant of the old "pyro-soda" developer, using tannic acid and enough sodium carbonate (aka washing soda, or in Europe, "household soda") to give a pH of around 10.5 to 11 (first guess would be 15-20 grams of tannic acid and 5-10 grams of soda per liter, but if you have or can easily get pH test papers you'll get a more consistent result). The solution won't last long (probably best to use within a half hour of mixing, and sooner might be better), but should produce usable results that will be distinctly different from the Parodinal you've been making.

 

[Jordan]

Tannic acid is interesting stuff. My Merck Index says that it isn't one compound, but rather a general name for a class of closely related compounds, mostly sugar esters of trihydroxybenzoic acid. The representative compound they give is an esterified glucose derivative.

An interesting experiment would be to dissolve a known quantity of tannic acid in a strongly alkaline solution (in a full, tightly-capped plastic bottle), let the solution stand for a day or two to hydrolyze off all the sugars, and then neutralize and use this solution to replace pyrogallol in a developer formula.

 

[ZorkiKat]

Thanks all, for the responses.

Phill, if sending powders through the mail would not get me arrested, I'd be glad to send you some . The stuff I have is fine, brown powder which resembles powdered Nestea, only finer. It assumes the same colour when dissolved in water too- in fact the solution looks just like iced tea. Been using it to tan pigskin. How do you use it for cyanotypes?

Thanks again, Donald and Kirk for the starting points. I'd like to see if the formulae you suggested would create stained negatives a la pyro. I've still a lot of soda/carbonate left- again from the tanning project. Does development in soda-pyro/soda-tannin require any changes in the film's rated ISO?

Jordan, "tannic" acid seems to indeed stand for several related compounds. In the tanning references, tannic acid is classified into two types, each rendering a slightly different effect in the leather it produces: pyrocatechols and pyrogallols. Getting these types identified by the actual developing agents gave me the idea of deriving developers from them.

 

[Kirk Keyes]

I'd like to see if the formulae you suggested would create stained negatives a la pyro.

Yes, it does make a staining developer, similar to Pyrocat -HD. Also, the tannic acid, when dissolved makes a slighty foamy, sudsy solution. I don't think there is anything to worry about. Also, the tannic acid may not all dissolve. I don;t think there is anything to worry about - it is a small portion of the initial amount, just filter it if you are concerned.

Because tannic acid is such a large molecule, about 2000 atomic mass units, that is why it should have less toxicity issues than pyrocatechol or pyrogallol, which are around 100-125 AMU.

 

[philldresser]

Thanks all, for the responses.

Phill, if sending powders through the mail would not get me arrested, I'd be glad to send you some . The stuff I have is fine, brown powder which resembles powdered Nestea, only finer. It assumes the same colour when dissolved in water too- in fact the solution looks just like iced tea. Been using it to tan pigskin. How do you use it for cyanotypes?

Zorkikat

Cyanotypes can be toned using Tannic acid in a weak solution (6g per 180ml) to acheives some lovely tan/brown combinations.The colour can be varied by adjusting the time/dilution. You can do this with Tea (most varieties) but the ingredient that causes the changes is Tannic acid.

I have attached 2 of my images as a before and after (with Tea)

For some tannic acid examples refer to Alan Jenkins site

Cheers

Phill

PS (This is not a hint) You can send powders through the post. You just need to make sure its well wrapped. I buy all my chems in powdered form from UK and USA and have had no issues.

 

[Ryuji]

But you can make a staining developer out of it. I've played with it just a little - try taking Pyrocat-HD formula, and substitute 10x as much tannic acid as the amount of pyrocatechol in the forumula. It works, and it should actually be a safer developer since the tannic acid is much less hazardous than pyrocatechol.

Tannic acid would react with gelatin, regardless of developing image. Does it really work the same as catechol??

 

[Ryuji]

Tannic acid is interesting stuff. My Merck Index says that it isn't one compound, but rather a general name for a class of closely related compounds, mostly sugar esters of trihydroxybenzoic acid. The representative compound they give is an esterified glucose derivative.

There are two general kinds of tannin. One is condensed (not hydrolyzable) and the other hydrolyzable. You read about the latter.

I posted a quick summary of tannin here:

Dead Link Removed

I don't know why I mentioned wine making as examples many times in that posting. Actually I know. I usually drink red wine when I waste my time in front of computer.

An interesting experiment would be to dissolve a known quantity of tannic acid in a strongly alkaline solution (in a full, tightly-capped plastic bottle), let the solution stand for a day or two to hydrolyze off all the sugars, and then neutralize and use this solution to replace pyrogallol in a developer formula.

The yield of active compounds that way will depend on the proportion of hydrolyzable tannin in the stock of "tannic acid" you use.

Polyhydroxy polyphenolic compounds were one class of candidate compounds I tested to improve stability of ascorbate developers but they are hard to use effectively due to solubility, other reactions, and indefinite composition of the raw stock. Eventually I found better compounds that are easier to use and more effective.

 

[Claire Senft]

What are the archival qualities of toning in tannic acids? Will toning work on regular fiber based papers?

 

[Ryuji]

What are the archival qualities of toning in tannic acids? Will toning work on regular fiber based papers?

Toning of cyanotype is a different story. Tannic acid reacts with iron to make dark (black) compound. Doesn't work with silver.

 

[Jordan]

The yield of active compounds that way will depend on the proportion of hydrolyzable tannin in the stock of "tannic acid" you use.

I found a website that discusses the content of hydrolysable and non-hydrolysable tannins in different sources, but I don't know what source "commercial" tannic acid comes from.

Dead Link Removed

 

[Ryuji]

I found a website that discusses the content of hydrolysable and non-hydrolysable tannins in different sources, but I don't know what source "commercial" tannic acid comes from.

It varies. I had a few stocks that all differed. Good suppliers should indicate the source. Sigma-Aldrich didn't indicate the source on the web but it was printed on the label. Some companies offered this info as well as the results of their assay right away, when I asked.

 

[Kirk Keyes]

It varies. I had a few stocks that all differed.

I used tannic acid that was from either Alfa-Aesar or Mallinckrodt - can't remember at this point... I do know that the Alfa-Aesar tests about 10% higher when doing the EPA test for Tannin and Lignin then the Mallinckrodt does. They are different in color/tint as well.

 

[Kirk Keyes]

Tannic acid would react with gelatin, regardless of developing image. Does it really work the same as catechol??

I would not say "the same" as catechol, as it need a larger amount relative to catechol. At least in the couple of proof of concept tests I tried substituting it in the Pyrocat-HD formula.

I think I used FP-4+ and the stain color of the developed film is similar to FP-4+ developed in Pyrocat. At least it is more like Pyrocat then say FP-4+ in PMK.

But it definitely is acting as a staining developer. I tried it tannic acid 1:1 for catechol, and I got a very faint image. I think I next tried 10:1 and got a pretty acceptable image. I have not done any comparison for sharpeness, accutance, or film speed, just a couple simple tests.

But I do think it would be neat to refine this type of formulation and see what can be done. And as I said, it should be a much safer (i.e. lower risk) developer to use than Pyrocat-HD.

 

[Kirk Keyes]

Jordan - did you see this page? Lots of intersting tannin chemistry:
http://www.users.muohio.edu/hagermae/tannin.pdf

And there's an old chemistry of photography book fromthe 1870s online that I think has a good description of the steps used in preparing tannic acid. I ssem to remember they understood that there were two forms of tannins even then.

 

[nworth]

Tannic acid would react with gelatin, regardless of developing image. ...

Could you expand on this a bit. Does it adversely affect the photographic qualities, or just harden the gelatin? You also mention other difficulties. Aside from the uncertain composition (which might very well lead to inconsistent results), could you expand on this a bit?

 

[Ryuji]

And as I said, it should be a much safer (i.e. lower risk) developer to use than Pyrocat-HD.

I am not sure about this point, because unless you analyze your solution, you don't know what's in the DEVELOPER you mixed. The info I gathered from your experience is that, by dissolving the compound in water, some compounds break down to make active developing agent(s).

It's also not very easy to deal with quantity that doesn't easily dissolve in water. It's also undesirable to have a compound that foams.

 

[Ryuji]

Could you expand on this a bit. Does it adversely affect the photographic qualities, or just harden the gelatin? You also mention other difficulties. Aside from the uncertain composition (which might very well lead to inconsistent results), could you expand on this a bit?

It is expanded in the link I gave before.

 

[Kirk Keyes]

Ryuji - "you don't know what's in the DEVELOPER you mixed"

Good point - but I don't think the tannic acid has to break down or hydrolyze while in solution to be effective. It's a polyphenol after all, and most of the proposed chemical diagrammes that I've seen show numerous polyhydroxy-groups on the benzene rings. Gallic acid is one of the structures found on at least one of the forms of tannic acid.

But then, what DO I really know about this? I guess it's easy enough to test - dissolve some tannic acid, mix up a developer, and then do a semivol extraction and analyzed it. Either of you guys have access to a GCMS?

Foaming could be an issue. How about a little simethecone? Filter the undissolved solids?? Like I said, it could use a little development work...

 

[Jordan]

Thanks for the link, Kirk. Pretty rich description of the tannins there. There are clearly lots of catechol and pyrogallol-like functionalities in them.

 

[Ryuji]

Good point - but I don't think the tannic acid has to break down or hydrolyze while in solution to be effective. It's a polyphenol after all, and most of the proposed chemical diagrammes that I've seen show numerous polyhydroxy-groups on the benzene rings. Gallic acid is one of the structures found on at least one of the forms of tannic acid.

Kirk, you are looking at it the other way.

Condensed fraction of the tannin will not be effective in development.

Hydrolyzable fraction (they are big molecules of sugar ester type) probably breaks down to smaller molecules when dissolved into the developer solution, and the fractions may even change over some time. Some of them work as a developing agent. The key point is that you don't know what is the active compound, and what are present in the solution. I would not conclude about the safety or consistency of the developer solution without doing a lot of testing, especially in absence of this knowledge.

Polyphenolic or phenolic compound does not mean that the compound is a developer. Certain groups have to be located in a way that they render developing properties. Gallic acid is a lousy developing agent, for example.

Anyway, tannic acid is an indeterminate compound mixture of plant origin. We can get better developers of known composition and purity at a lower price. I don't see a reason to go for tannic acid despite all the practical problems and lack of precise knowledge.