Picture frame glass and acrylic glazing

Glazing is the part of a frame people think least about and pay most for. It is also the part that decides whether the artwork survives twenty years on a wall.

The two families

Everything sold as picture frame glazing is either glass or acrylic, and the trade-off between them is almost entirely about weight and breakage.

Acrylic is sold under trade names including Plexiglas, Perspex and Lucite. All are the same polymer — polymethyl methacrylate — with different manufacturers behind them. The meaningful distinction is between cast acrylic, which is optically superior and slightly harder, and extruded, which is cheaper and marginally softer.

The one material to avoid is styrene, the very thin plastic sheet supplied with the cheapest ready-made frames. It scratches from dusting, yellows within a few years, and is noticeably wavy. If a large frame is unexpectedly light and the glazing flexes easily, it is styrene.

Choosing by size

The decision is essentially settled by dimensions.

Up to 11x14: glass. Light enough not to matter, and the scratch resistance is a genuine advantage on a frame that gets handled.

16x20 to 20x30: either. Glass is fine on a solid wall fixing; acrylic makes sense if the frame will move, ship, or hang above furniture.

24x36 and above: acrylic, unless there is a compelling reason. A 30x40 sheet of glass weighs around ten pounds, is awkward to carry, flexes under its own weight, and produces genuinely dangerous fragments if it goes.

Anywhere a child sleeps or plays, and anywhere above a bed or sofa: acrylic, at any size.

Anything being posted or couriered: acrylic. Glass in transit is a coin flip.

The four glass grades

Beyond plain glass, three upgrades are sold, and they solve different problems.

Clear float glass

The default. Around 45% UV transmission blocked, a faint green cast from its iron content, and full reflectivity. Cheap, hard, and perfectly adequate for reproductions and posters.

Low-iron glass

Chemically the same, with the iron reduced so the green cast disappears. The difference is subtle in isolation and obvious side by side, particularly on artwork with large white areas. A modest premium; worth it for photographic prints and anything with delicate paper tone.

UV-filtering glazing

Blocks 97% or more of ultraviolet light. This is the upgrade that actually preserves artwork. Light damage to paper and pigment is cumulative and irreversible — a print in a bright room fades measurably over a decade — and UV glazing is the only glazing feature that meaningfully slows it.

It does not solve everything. Visible light also fades pigment, and no glazing stops that. Do not hang irreplaceable work in direct sun regardless of what is in front of it.

Museum / anti-reflective glass

An optical coating on both faces reduces reflection from roughly 8% to under 1%, alongside UV filtering. The effect is startling: the glass reads as absent. It is the most expensive glazing available by a wide margin and the correct answer for original artwork in a well-lit room. For a poster it is simply money.

Non-glare glass: the honest assessment

Non-glare glass is etched on one surface so that reflections scatter rather than mirror. It is cheap, widely stocked, and often the default in ready-made frames.

It works, and it costs you something. The etching also scatters the light coming from the artwork, which softens fine detail and adds a faint milky haze. Crucially, the effect gets worse with distance: pressed almost against a document, non-glare glass looks fine; separated from the artwork by an 8-ply mat, it visibly blurs it.

Where it is right: documents, certificates and text-heavy pieces in corridors and offices with overhead lighting, especially behind thin or no matting.

Where it is wrong: photographs, anything with fine detail, anything behind a thick mat, and anything where the tonal subtlety is the point. For those, the better answer to reflections is anti-reflective coated glazing, or moving the frame.

Cutting and sourcing

Framing shops, glaziers and many hardware stores will cut picture glass to size for a few dollars a sheet. Ask specifically for 2mm picture glass — the 4mm glass sold for windows is unnecessarily heavy and will not fit a standard rabbet.

Take the frame with you if you can, or the exact rabbet measurement. Glass should be cut about a sixteenth of an inch under the nominal size in each direction so it drops in without binding.

Acrylic is easier to source and can be cut at home with a scoring tool and a straightedge: score repeatedly along a line, then snap over an edge. Leave the protective film on both faces until the moment of assembly.

Cleaning, without ruining anything

Two rules cover almost every mistake.

Spray the cloth, never the frame. Liquid sprayed at a frame runs down the glass, past the rabbet, and onto the mat and artwork, where it leaves a tide line you cannot remove.

Never use ammonia-based cleaner on acrylic. Standard blue glass cleaner crazes acrylic — producing a network of fine surface cracks — permanently and often within a single cleaning. Use a dedicated plastic cleaner, or plain water on a microfibre cloth.

For glass, a microfibre cloth lightly dampened with water handles almost everything; a drop of isopropyl alcohol deals with fingerprints. Paper towel is abrasive enough to leave fine scratches on acrylic and leaves lint on glass.

Keeping artwork off the glazing

Paper and glass in a humid room will eventually stick to each other, and photographic emulsion does it faster. Separating them afterwards is a conservation job with a poor success rate.

The gap is provided by either a mat, which is the usual and best solution, or by clear plastic spacers — thin strips that sit in the rabbet at the frame's edge and hold the glazing a fraction of an inch proud of the artwork. Spacers are what you use when the design calls for no visible border, as in a float frame.

Pressing artwork directly against glazing with nothing between them is the single most common cause of avoidable damage in home framing.