The old Japan finishes were basically a baked on varnish with asphaltum as the coloring agent.
It looks to me like you're stripping off the old shellac.
The 99 I'm working on for my daughter has a very badly damaged shellac clear coat. Most of it is going to come off whether I like it or not. The machine didn't look too bad at first, just some alligatoring is what I thought. It turns out the entire coat of shellac was basically floating on top of the black. It's a pretty big mess at the moment. I figure I'm better off taking it off as gently as I can and then I'll either wipe or spray on a fresh coat.
Rodney