Picture-frame glass -- or glazing -- is frequently used in thicknesses from 2.0 mm to 2.5 mm. The 2.5 mm thickness is standard for most framing glass, including coated glass that protects your artwork from fading, such as conservation and museum glass. Anti-reflective, water white glass, a low-iron glass without the green undertone, is available in a 2.0 mm thickness, while acrylic glazing comes in sizes up to 6.0 mm.
2.0-mm Glass
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The 2.0 mm thickness of water white glass is useful when smaller frames are packed extra-full. A frame's rabbet -- its depth from outer edge to lip -- is sometimes too shallow to accommodate a mat and fillet, especially when the mat is built up with foam-core underneath to avoid drooping sides. Even when thin mat board is used for backing, 2.0-mm glass often prevents stapling problems.
2.5-mm Glass
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For most framing projects, 2.5-mm glass is a reliable choice; its thickness is as suitable for an 8-by-10-inch frame as a 32-by-40-inch frame. This is the thickness of most-inexpensive, regular framing glass, and it's also the thickness of conservation glass and the virtually invisible museum glass, which filters 99 percent of UV rays.
3.0 mm, 4.5 mm and 6.0 mm
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Extra-large frames and frames that hang in places where maximum safety standards apply, such as schools, benefit from acrylic glazing. In thicknesses from 3.0 mm to 6.0 mm, this glazing alternative includes anti-static options for framing large drawings in dry media, such as charcoal and pastel.
