Finish softens with meths - what is it

Hi. We have some mid-century Parker dining chairs that I’d like to redo. The finish on the timber is still pretty good so I don’t want to refinish, just reinvigorate. I believe they were made in the sixties or seventies. I tested some surface with meths and it softened the finish. I know that’s typical of a shellac finish but the period doesn’t sound right for French polish - more likely nitrocellulose or some other type of industrial lacquer.

I also noted that when some finish was removed the grain looked white, as though filled with that white powder (can’t remember what) used as a grain filler which I typically associate with French polishing.

So my questions are.
1. Does meths soften nitrocellulose, or anything else used in the period besides shellac?
2. Anyone know what Parker and other makers used in this period? I googled this, a lot of speculation but no-one who actually knew.
3. Can anyone recommend a good wipe-on rejuvenation product - if it’s shellac or if it’s nitro? I’d just like to make them look their best with minimal interference.

Attached is photo, in case it helps.
Cheers
Arron

Also, I’ll be putting a post about reupholstering these in the upholstery subforum. If you know anything about chairs of this period please have a look.


Attachment 533594

Sounds like shellac or french polish to me. Particularly the white filler.