On Fri, 19 Sep 2003 07:32:11 GMT, "OzSawdust"
wrote:

I have been restoring an English solid oak desk (circa 1910 - 1920).

Could it be some sort of varnish?

Could well be. Spirit varnishes (natural resins in alcohol) would be
in period. These resins don't dissolve in alcohol unless heated, and
after years of exposure in a thin film they may be so oxidised they'll
never dissolve again.

You can try a few other solvent-based strippers. Dichloromethane and
methanol (a commercial stripper recipe, sold as Nitromors) may work.
If it's just very old shellac, you could try ammonia too.

If you can't soften it in situ, then scrape or sand may be
appropriate.