I?ve made a lot of framed Intarsias and have found that if I make my frames, following this basic RULE OF THUMB, they turnout visually appealing:
Split the difference over the height and the width to determine the frame width. 1? = 1 foot
So, if a picture is 12? x 12? then make the frame 1? wide.
A picture that is 12? x 24? then split the difference and the frame would be 1.5? wide.
A 36? x 60? picture gets a frame 4? wide.
(On Large pictures if you make the frame ?? wider or narrower it?s OK, it?s still within the Rule Of thumb).
Hope this helps. Al