I just bought an 1880 colonial with all the original doors and hardware. The doors are stained not painted but the finish is weird. The clear coat/varnish has gotten all bumpy. It looks like someone applied a paint remover but never sc****d it off and it ended up hardening. Is this old varnish? How do I correct it? I have seen old doors for sale at flea markets that have the same bumpy texture. Please help!