Glazing materials should be separated from the artwork. Glass is prone to condensation. Moisture builds up inside the frame where there is no ventilation and can contribute to the deterioration of the artwork. Acrylic generates a great deal of static electricity and can cause the artwork to transfer to the glazing material itself. (This is especially true of charcoals and pastels.)

The first technique to separate the glazing from the artwork is to use a window mat. The window mat should be thick enough to create a separation between the glazing material and the paper art. Ply is the term used to describe the thickness of matboards. Standard matboards range between .050 – .060 inches in thickness. 4 ply museum board is approximately .060 inches in thickness. Both can be used for mats or backing boards. Thicknesses less than the above are generally used for backing boards or barrier papers. Double mats as well as 6 and 8 ply boards are available when additional depth is needed.

The second technique is to use spacers. Spacers are the material used to separate the glazing material from the artwork when mats are not used

To understand glazing products it is necessary to understand the effect of light on artwork.

This chart illustrates the different light wavelengths. The unit of measure of light wavelength is called a nanometer.

The most damaging light is the ultraviolet which is in the 200 to 400 range. This light is powerful enough to induce photo chemical damage to organic material resulting in: loss of color, yellowing, bleaching, darkening and embrittlement.

Visible light is between the 400 – 700 range. (Above 700 is infrared light which is heat.) Within the visible spectrum of light the range between 400 – 500 which are the violets and blues also are damaging to artwork. Although light cannot be filtered out entirely without eliminating these colors there are products on the market that filter out ultraviolet light. The following gives statistics on how effective UV filters are:

	%blocking	%blocking
	300-380 nm	300-400 nm
regular glass	46.59	39.64
regular glass w/UV filter	99.17	93.10

Although we do not have comparable statistics on acrylic, all the data we have reviewed indicate that regular and UV filtered acrylic would be at least as effective as regular and UV filtered glass.

When should I use glass and when should I use acrylic?

Glass is the most commonly used material for protecting artwork on paper. The advantage of glass is it is less expensive, easy to clean, and does not easily scratch. The major advantage of acrylic is that it is virtually unbreakable. We recommend using acrylic when artwork is being shipped. When frames are over 32×40, you should consider acrylic because it is 1/2 the weight of glass.