CHALK AND PASTEL
If you touch the surface of art made with chalk or pastel it can smear, whether it is new or old. To prevent this, pastels are placed behind glass. When a pastel is matted, the hard edge of the mat can leave a permanent impression in the art. To prevent this pastels are often floated on top of a mat. If the framed work is ever bumped, dust can migrate from the art onto the glass or can be trapped between the glass and mat. This problem is overcome by adding a second mat with a window opening and a spacer between it and the art. This will provide a space for the dust to fall behind the mat where it will not be visible.
Acrylic glazing is more susceptible to static electricity and the static can “pull” dust particles from the work. The use of Acrylic glazing should be avoided with these works.