"Gregory Moreton" wrote in message
news:1124269199.10efc1e59cf80fbf5c9a91871d03c561@t eranews...

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.


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.