There are a couple of pages on French polishing in a Sunset [Magazine]
Book titled "Furniture Finishing & Refinishing".  It is a method of
alternately applying shellac with boiled linseed oil by padding and
then rubbing it out with rubbing oil and pumice or rottenstone, over
and over and over, until you get what you want or wear yourself out.

Don Shenbarger

 [ My 7 kg dictionary of 1927 says that "rottenstone is a friable
 [ siliceous stone, the residue of a decomposed siliceous limestone
 [ whose calcareous matter has been removed by the solvent action of
 [ water.  Cf. tripoli."  In German it's "der Stinkkalk" = smelly lime!
 [ -- Robbie