We were asked by a customer to re-frame two very old watercolors that had been framed many decades earlier. The frame was cracked and chipped, the glass was dirty and the customer really wanted a different mat color as the original was very dark. Upon taking it apart, we discovered that the artwork had been taped (or glued) to the original mat and could not be removed without risking further damage.
A new frame was put on, a new and brighter mat was used, but still preserving the old mat as an accent piece and the result is two brighter, bolder pictures that would look good on any wall.