A carved, moulded, or illusionistic surround for a painting. The purpose of a frame is two-fold: the protection of the painting, and the enhancement of its appearance through decorative and architectural features that may relate it to its surroundings. The first frames, for example in early Renaissance altarpieces, were integral to the structure of the painting and are described as ‘engaged’. With the increasing secularization and privatization of art, picture frames came to be produced independently of the paintings themselves. The most significant initial developments of the independent picture frame were in Italy, but by the late 17th century Paris had become the most important centre of production. Middle-class demand for frames reached a peak in the 19th century, though mass production led to a general lowering in quality with less robust and detailed moulding often replacing more traditional but expensive carving. The majority of frames are gilt, but different finishes have also been favoured, particularly in northern Europe, and some of the Impressionists preferred white painted frames. The 20th century saw a questioning, and in some cases a complete rejection, of the necessity for the picture frame, its aesthetics perceived to be at odds with those of much of modern art. Simple edging, either wooden or metallic, has often been employed. Very few historic pictures are housed in their original frames, reflecting the vagaries of taste and physical circumstance.