Posts Tagged: picture framing glass

The Framing Glass—or rather the lack of it

Thoughts and evaluations of Anti-Reflection Picture Framing Glass

Introduction
This article is targeted mainly at artists, custom framers and conservators who are particular about the way artwork is presented, preserved and protected. If you are squeezed for time, skip to the evaluations here, or the conclusion here. But if you are new to all this I suggest reading from the beginning.

Revisions:
9 Sep 2015 Changed spectral graphs to include UV spectrum, revised article language.
9 Nov 2016 Revised article language. I have since received samples from the other manufacturers of AR glass, and am awaiting samples of newer products such as Artglass UV99 and the new “ripple-free” Museum Glass. Some of my conclusions and recommendations will be revised in light of the performance of these new and updated products in a future article.
2 Jul 2017 Revised article language.
5 Aug 2020 Updated product names to reflect manufacturer changes. The illustrations still retain the old naming conventions, so watch out!

As a maker of finely crafted prints, I want them to look as good as possible, so it is rather bothersome when we cannot see them as well once they are framed behind glass, due to its obtrusive reflections and greenish tint. Framing without glazing is out of the question for fine prints in the interest of long-term preservation. It shields the art from physical damage, atmospheric pollutants and to varying extents, degradation from ultraviolet (UV) light. What we need then is highly transparent, anti-reflective glass.

Uncoated “regular” soda lime glass (and clear acrylic) reflects about 8% of light in total (4% off each side). The glass itself absorbs another ~2% or more of light. But the absorption is not uniform across the visible spectrum. Iron oxides naturally present in silica, the main ingredient of soda lime glass, is responsible for its green tint. This is most visible when looking at the edges of float glass. Low iron glass is manufactured from silica with very low iron content. This makes the glass almost completely neutral in colour and light absorption is reduced to about 0.5% or less. Clear acrylic has the advantage of having absolutely no colour tint and absorbing virtually no light at all.

To increase the transparency of glass still further, we need something else to reduce surface reflections—anti-reflection (AR) coatings.

Artglass specifier frame comparing regular glass to anti-reflection glass.

Artglass specifier frame comparing regular glass to anti-reflection glass.

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