These box frames are made from tulip, which is a good wood for painted and gilded finishes. The frame in the photo above has a sprayed on gesso base which is given a coat of white primer which is then sealed with a matt varnish.
The frame in the top photo is the same as the first, but after the primer coat it has had a bright white gloss spray finish which is sealed and protected with a gloss varnish.These frames are very simple and cleaning looking, with seamless corners as the mitres are not visible. It is also possible to spray directly onto the wood, building up the paint layers to get a solid finish.