I am refinishing wood kitchen cabinets, about 1950-ish. I started out
with Citistrip and then changed to methylene semi-paste. I thought one
bottle of Cit. was junk, as it would not soften the finish, so I
switched (not mixing the two, of course). Even with the methylene, some
of the finish is barely softened...seems to be the base coat, mainly
inside of cab doors. This is bizarre, as I've done tons of refinishing
and never encountered this. This tough finish doesn't soften much, even
after leaving meth. stripper on for an hour or more. I lift off as much
of the stripper as I can with a wide plastic scraper so I can reuse it.
This finish - some kind of varnish stain?? - is still in place and
requires scraping hard with a metal scraper. If I don't scrape it off
ASAP after removing the stripper, it doesn't want to come off. Scraping
it right away yields a pile of fluffy stuff that looks kind of like
cellulose insulation - almost dry and kind of powdery.

This house was built like a fortress, may have been owner built, and
cabinets are kind of different...plain, thickish veneer over wood
strips...can't imagine what finish was used. Seems like some doors have
another finish??!