I thought it would be fun to take a look back at Mallory's very personal salon-style wall of art. (It's always intriguing to see what designers do in their own homes.) Notice that the frames do not all "match," but rather harmonize? I think this really suggests a collection that evolved over time instead of something put together in a day. And the frames and mats seem to have been chosen to best highlight the art, not to decorate the room.
Interestingly, Mallory used many dark frames against Farrow and Ball's "Mahogany" paint in full oil gloss to achieve a sort of faux lacquer effect. She notes that this isn't the same as professionally lacquered walls, but she was able to get the look she desired at a fraction of the cost.
Pictures courtesy the designer.