Frames are pretty boring, but extremely simple to make. No real load on them, no technical demands, just cut a rabbet big enough for whatever you’re going to stuff in there and make four structurally reasonable right angle joints. For the simplest ones I’ll just screw a plywood sheet behind the corners, it gets it very flat and tough and nobody’s going to be popping the picture out and replacing it anyway. Maybe one of these little keys over the front miters, to cover the seam
If you’ve got some cool looking material to work with, you’re done, everyone loves figured wood.
If the material sucks, just stick a thing on it, go crazy. This thing was originally a stack of firewood, all about 6″ long
On occasion, you get one with more complex demands
