Metropolitan manufactures custom floating frames with spacers which are used to separate the glazing materials 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.) One technique is to use spacers. Spacers are the material used to separate the glazing material from the artwork when mats are not used. Metropolitan has wood, plastic, and 8 ply rag board spacers. The other 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. Metropolitan custom cut mats are available in both 4 and 8 ply boards.
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 w/UV filter||99.17||93.10|
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.
Metropolitan sells both regular and ACRYLITE UV filtering (OP-3) acrylic. The OP-3 version protects from both natural and artificial light. Continuously-manufactured ACRYLITE UV filtering (OP-3) sheet filters out 98 percent of damaging UV rays, protecting paper-borne artwork, prints and documents from fading, yellowing and brittling. ACRYLITE sheet’s UV protection is part of the structure of the sheet, it can’t scratch off!