At a recent exhibition at the Detroit Institute of Arts, I noticed a very nice matting technique. I'm not sure how exactly it was done, so I'm hoping someone here has some idea. I don't have a photo of it since it wasn't allowed. (No photography allowed in the photography section - how ironic).

So, the windows on the mats were as normal, except that instead of a hard edge where the bevel is, it was rounded over. Does anyone know how this is achieved? It almost looked like a very small rounding plane was used.