I was poking about on the Web to learn more about the history of frames, and for anyone who is interested, there is a wonderful website done by Paul Mitchell, an antique and reproduction frame-maker and conservator of paintings in the UK. Entitled "A short history of the Frame", it makes for concise and fascinating reading for anyone who is interested in how a frame can enhance (as well as protect) a work of art, as well as the evolution of frames.
By the same token, the changes in taste that dictate a type of frame on a painting at one point and an entirely different one at another period are wonderfully chronicled by a short paragraph about the framing over time of the Mona Lisa, Leonardo da Vinci's masterpiece hanging in the Louvre.
It reminds me of a wonderful story told with great glee by my beloved godfather, the late Reverend Richard H. Randolph, SJ. He was standing in front of a painting in London's National Gallery one day, and turning to his companion, he remarked that he felt the frame was entirely wrong for the work of art. He then described how he would re-frame it, and as he was talking, he noticed a distinguished-looking man was standing behind him, listening intently. He thought no more of the incident until, on his next visit to the same Museum gallery, he saw that the picture in question had been re-framed ... exactly as he had described! The gentleman behind him turned out to be the then-Director of the National Gallery, an attentive audience!