I agree with you concern about indenting the paint. Here's a variation that I believe might work. It's similar to the original method of attachment, but allows the frames to be joined and finished in my shop.
As my concern is that prejoined frames would be difficult to fit to any possible variations to the outside edges of the paintings, I would have 4 additional pieces, 1/8" thick, that would be cut on site and attached to the painting outside edges, flush with the front. All that would be seen of these pieces would be about 1/16" of the front edge. They would be finished just like the rest of the frames. The frames would then attach to them like before, with some finish head screws. or the frames could be held on with several small metal mending plates attached to the back which would give a cleaner appearance overall.
posted on Jun 09th 2012 by James Eddy Woodworks