I was wondering if anyone has ever engraved wood that already has a finish on it.
By finish, I mean a nominally clear finish such as polyurethane or tung oil or varnish, etc.
One finish I have been trying for outdoor use is to dilute activated acrylic casting resin with acetone
and then brush on for deep penetration of the acrylic into the wood.
Since PMMA, e.g. polymethylmethacrylate, AKA plexiglas, is a good laser cutting material,
wood that has been hardened in such a way may be a good candidate for laser etching.
The Proofgrade is finished and I’ve done some cabinet toe kick board that is pre-finished. Doesn’t seem to make a difference. Are you talking about a thicker coating to just engrave or go all the way through?
There is an interesting message now in the Glowforge UI that discusses the possible issues with unknown materials and their glues and finishes. This is a good topic to bring up.
Most finishes have limited penetration into the wood and are designed to be more of surface treatment like paint.
Oil finishes do “soak-in” to a limited extent; however, they are not typically used in commercial applications
due to the multiple steps required.
My query about thinned acrylic resin came to mind, because it does soak-in due to the dilution with acetone.
I have not measured the penetration, but the woods I have tried can absorb a surprising amount. This is not a thick surface layer, but a deep penetration into the wood fibers. This is similar to the wood hardener that can be purchased.
Of course, that is always a concern. In this case, the polymer is exactly the same as in acrylic sheets
that cut so well with the laser. The only difference is that it is polymerized in place and inside the wood matrix.