Why Glass Is Important for Framing Your Art Work?
The primary purpose of glazing in art framing is to physically protect the work of art from damaging factors such as humidity, heat, and soiling. Laminated glass and some acrylic may be used to protect against physical damage from glass breakage and to offer protection from a malicious attack. Regular glass as well as some glass surface treatments can also filter some of the damaging ultra-violet radiation (UV) and heat (NIR). Artworks that require protective glazing are those rendered on paper or fabrics (including photographs), which contain pigments and dyes that absorb UV and are susceptible to discoloration.In the case if the framed object or artwork is UV resistant, UV protection can still serve the purpose of preserving the integrity and colors of non-conservation grade framing materials susceptible to UV damage, such as mat board (passe partout).
Although protection is a primary purpose of glazing, displaying an artwork is the primary purpose of framing it. Therefore, the least visible glazing best displays the artwork behind it. Visible light transmission is the primary measure of glass' invisibility, since the viewer actually sees the light, reflected from the artwork. Light transmission of glass is especially important in art framing, since light passes through the glass twice – once to illuminate the artwork, and then again, reflected from the artwork, as colors - before reaching the viewer.
Light transmission (for this article, the perceivable visible spectrum between 390 nm and 750 nm is considered) through glass is diminished either bylight reflection or light absorption of the glazing material. The total light transferred through the glazing material (light transmission) is reduced by reflection and/or absorption. In art framing, light reflection causes glare, while light absorption also may cause the transmitted colors to be dulled or distorted. While type of the glass substrate will affect the light absorption of the glazing, the surface treatment can affect light scattering, light reflection and in some cases, light absorption. There are various glazing options to achieve this goal as explained in the following sections on Types of Picture Framing Glass.
Types of Picture Framing Glass
Regular (or "Clear")
Due to widespread availability and low cost, Soda Lime Glass is most commonly used for picture framing glass. Glass thicknesses typically range from thin 2.0 mm, to 2.5 mm. Clear glass has light transmission of ~ 90%, absorption of ~ 2%, and reflection of ~ 8%. Whereas absorption can be reduced by using low-iron glass, reflection can only be reduced by an anti-reflective surface treatment.
Low-iron (or "Extra-Clear," "Water White," etc)
Low-iron, or water white glass, is made using special iron free silica, and is generally only available in 2.0 mm thicknesses for picture framing applications. Because low iron glass light absorption can be as low as 0.5% vs. ~ 2% for clear glass, the light transmission will be significantly better vs. clear glass. Low iron glass has light transmission of ~91.5% and reflection of 8%.
Laminated glass offers shatter-resistance and protection from malicious breakage to art glazing. The most commonly used configuration is Glass + PVB Foil + Glass. Some variations of foils and glass thicknesses can offer shatter- and breakage-resistance or even bullet-resistance. The absorption of laminated glass depends on the glass substrates and foils used in the laminating process. Reflection of laminated glass is similar to monolithic glass, unless surface treatments are applied to reduce reflection.
Some types of acrylic glass can have the high light transmission and optical quality of glass. Acrylic is also light weight, compared to glass, and is shatter-resistant, making acrylic an attractive choice for framing large, over-sized works of art. In general, acrylic sheet scratches easily and retains a static charge, which can be problematic when framing pastels or charcoals. Some manufacturers, add dyes to acrylic glass to filter the UV light transmittance, and its surface can also be treated with both anti-static and anti-reflective coatings.