Where picture framing is concerned, there are several advantages and disadvantages of plastic glass glazing ( to glaze is to cover the surface of something with a pane or film of covering material ) over glass glazing in using it for indoor (as against outdoor) picture frames. For picture frames, the most common acrylic glazing material used is cast plastic rather than the extruded or 'continuous' type. The reason for this is that the former is of higher quality has less impurities and harder and thus a little harder to scratch. Nowadays ...