tannin or tannic acid

I take it you never tried a simple Google search?

Type in Tannic Acid for a few more than 99,000 hits. You don't even have to follow the hits though. On the top right of the results page there is this link:

Eric

Before you get too carried away trying to by tanic acid you will find that oak sap is probablly the best source. In fact many woods produce it to some degree as a sort of natural preservative.

The "Mix" I use for ebonising contains the "juice scraped from the underside of freshly stripped oak bark". I think I picked up the idea from an old book I found in the library on antique restoration many years ago. The basic recipie for which includes finest malt vinigar, swarf from the local engineers shop ( or wire wool ), oak sap, horse urine and for some reason an old penny coin. The latter being I suspect for the copper but I can't see why.

A modern penny probably does not have enough copper to make a difference and personally I don't know any horses.

Gregory Moreton RPT

Other tanbark trees, for instance elm, or in US, hemlock are also a source. The copper is used to speed the chemical reaction electrically, by sacrificing the more electronegative iron. Of course, a piece of copper piping or a fitting will do admirably. Perhaps a bit of urea-based nitrogen fertilizer will substitute for the horse.

Visions of "A Funny Thing Happened on the Way to The Forum" keep cropping up in my head....

Oh yes, if you don't take the time to strip the oil off that steel, you'll have a longer wait. It does offer protection against corrosion. Solvent wash just fine.

as a lab technician i ahev access to tannic acid and have used it with great success and you are right you can ebonise any wood if you mix an Iron III salt (rust) with the tannic acid and just treat the wood as usual. of course you may have a bit of trouble getting it - check through your local chemist of chemical supplies to education - they might be able to help