But I do have a large stash of white metal frame pieces (Nielson profile #11 it looks like -- no sizes I normally use, nor the color). I'll have to inventory the pieces and take them to a frame shop and have them re-cut for me (thanks Ian -- I have been trying to figure how to cut them myself). Perhaps I'll spray paint them a nice semi-gloss black.
I have mounted a lot of 16x20 (image usually 15x19) on 20x24 -- why? Because one can get two 20x24 sheets out of a 32x40 sheet of matboard, an important cost-factor as a student and soon after. But in the long term, a big mistake -- the 2 inch borders is not enough.