Intergalactic_Captain
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Extraction of gallotannin - Ideal method?
So, the other day I was roving wikipedia and came across the topic of leather tanning. I know it ain't news to a lot of you guys, but as it turns out
Sumac (I'm using staghorn) is 4% by weight gallotannin - Not sure if that's wet or dry, but either way it's a rediculously huge number for most useful
plant chemicals. Some research has shown that the traditional method is probably the best on a large scale, ie. the use of water to extract the
tannin. I've 3 basic methods to choose from;
1 - long, cold steep in water at ambient temp
2 - shorter steep in 40-60degC water
3 - My steam stilll, basically a 55-gallon retrofitted moonshine still which runs a steam line to 2 stacked 5 gallon buckets, the top (packed with
plant material) with a hole to let condensate drip to the bottom one.
I'd like to go with #3, I've already proven its utility on a few other plants. However, I'm worried about heat - Every reference I've seen says that
the hotter you extract, the darker your leather will tan... Are we talking oxidation, polymerization, coagulation, or something else? If someone
could elaborate on the chemistry here I'd greatly appreciate it.
Ideally I'd like to have a dry, solid product for ease of use. Merck says that chlorophylls are soluble in benzene (while gallotannin isn't), so I
figure a couple of organic washes on a concentrated aqueous tannin extract should take care of that plus any natural waxes.
Oh, and I'm not planning on tanning leather, so please keep your answers to the chemistry rather than the history.
If you see me running, try to keep up.
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12AX7
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It's my understanding that galls (oak gall "nuts", nubs seen on the underside of leaves, etc.) and oak wood in general are quite rich in gallotannins,
to the tune of tens of percent.
I once tried making a "gall tea", but got no reaction at all with iron (it should instantly form a purple-black complex).
Tim
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UnintentionalChaos
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I believe only certain types of galls work for that. Red oak acorns sure as hell work. Boil a few in water and then add a tiny bit of ferrous salt
solution (I had rusty nails soaking in vinegar) and it goes inky-black. I did this before I even really got into chemistry as an attempt to dye cloth
black without store bought dyes (I got gray at best).
http://www.scrd.net/scrd_new/anglais/c_nat/extraits_veg/suma...
This suggests that the tannins break down under heat, which is undesirable for tanning leather. I'd pulverize the dried leaf matter and extract with
warm water, then evaporate.
[Edited on 7-17-08 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Intergalactic_Captain
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I actually read that one the other day, can't believe I didn't remember it...I suppose I'll probably go with warm water. I'm waiting on the leaves to
dry now, they're turning a nice healthy brown. And yes, I understand that galls are the best, but I could quite literally pick a half ton of leaves
and barely put a dent in the amount of sumac growing around me.
If you see me running, try to keep up.
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Ozone
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You can solublize many polyphenolic compounds by treatment with alkali at high temperatures.
I have seen extracts made this way turn black on contact with air, which implies oxidation to quinone-form and subsequent oxidative addition.
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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