Varnish has aliphatic hydrocarbon thinners ("cold"). Lacquer has aromatic hydrocarbon thinners ("hot"). So the thinners in lacquer will partially dissolve the varnish (maybe making it wrinkle) but not the other way around. But most old pianos are shellac, to which anything sticks well (as long as all surface contaminants are removed) so I'm wondering what application you are contemplating. (Just curious.)
Thumpe
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20120827/e0ac0e29/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC