John Tuttle asks about a crude oil finish.

This may have been Old English polish.  It seems everyone dealing with
antiques used it to cover scratches.  We've also heard of using crude
oil, but the oily residue would prevent proper bonding of any new finish
applied over it.  We have stripped pianos and found dark oily lines where
the original finish had cracked.   We assumed this could have been "crude
oil" or Old English.

An acceptable touch up material can be made from a mixture of asphaltum
and solvents, such as naptha.  This was actually used as a staining
medium in years past.  An easy source for asphaltum is roofing cement.
A quart container will give you enough coloring for at least 100 pianos!

Bob Lemon¶
Lemon's Player Piano Service¶
Sacramento, CA