Michael Dresdner

straight talk about wood finishing

Reversing time

Q: I’ve looking at a restoration issue in some of the old Chicago bungalows where what I assume is varnish has almost coagulated on the surface of the wood trim. On most of the woodwork it’s acquired a nice patina and I’m trying to figure out how we could smooth the surface without removing the patina.
A: That depends largely on what you are defining as patina. That term, borrowed from the metal industry, actually refers to a specific kind of oxidation, but people in the wood industry use it to mean a variety of things, from the change in the color of wood itself beneath a clear finish, to changes in the finish atop the wood, and various combinations of the two.
If you mean the former, you can chemically strip wood without sanding it, and thus without altering the sun fading or darkening that occurs through a clear finish. On the other hand, if you are referring to anything in the finish itself, almost all finish aging, from clarity to color to sheen, can be copied. That’s the finishing part of the art of antique reproduction.
Some older finishes, notably shellac and similar natural resin spirit finishes, will form coarse globs of finish on what was once a smooth surface. Many of these can be dissolved and redistributed with a material called amalgamator. That’s tricky stuff to use, and if you have not used it before, I would not try it out on something that matters. The idea is that you can keep the original finish itself, with the wood color and even finish discoloration still intact, and simply reflow it.