Matting & framing glossary: the terms explained

This glossary defines the matting and framing terms you'll meet on this site and on custom-framing order forms — including the US, UK/Australian and European words for the same thing. A mat in the US is a mount in the UK; the window is the opening or aperture; and the French and Germans call the whole thing a passe-partout (Passepartout).

Below, the terms are grouped by what they describe — the board, the spacing, the cutting, the sizes, and finally the dialect differences. Read straight through, or skim the dialect table at the bottom if you're decoding a foreign order form.

The board and its parts

Mat / mat board (US) = mount / mount board (UK & AU)

The flat card with a window cut in it that sits between your artwork and the glass. Americans call it a mat; the British and Australians call it a mount or mount board. Same object, two names. (Confusingly, in the US "mounting" means a different thing — see the dialect notes.)

Ply (4-ply / 8-ply)

Ply describes mat-board thickness, with 4-ply as the common everyday board and 8-ply as a thicker museum-style board. Thicker board gives a deeper bevel and more presence, but it also needs a cutter set up for the extra depth.

Opening = window = aperture

The hole cut into the mat that shows the artwork. "Opening" and "window" are everyday US terms; "aperture" is the more formal word common in the UK trade. It's cut a little smaller than the art so the edges are held — see overlap.

Bevel

The angled edge of the opening, normally cut at 45 degrees so it slopes away from the artwork. A bevel exposes a thin line of the board's white core and catches the light, which is why a beveled window looks crisp where a straight-through (vertical) cut looks blunt.

Undermat

The lower board in a double mat. Its window is cut slightly larger than the top mat's window so a sliver of it shows through — that sliver is the reveal.

Single mat vs double mat

A single mat is one board with one window. A double mat stacks a top mat over an undermat to add depth and a color accent. Triple mats exist too, but two is the common upgrade. See our double matting & reveals guide for how to size them.

Borders and spacing

Three small numbers do most of the work here: the overlap, the border and (for double mats) the reveal. Get these right and the maths downstream — opening size, outside size, frame size — falls out automatically.

Overlap

How far the mat covers the edge of the artwork on each side, usually ⅛″ to ¼″. The overlap is what stops the art slipping through the window. It's also why the opening is smaller than the art: opening = art − 2 × overlap.

Border

The visible width of mat face from the opening edge out to the mat edge — the breathing room around the picture. Borders can be equal on all four sides, or wider at the bottom (see bottom-weighting). Set yours quickly in the mat border calculator.

Reveal

In a double mat, the thin strip of the undermat that shows around the window, typically ⅛″ to ¼″ wide. It reads as a slim accent line between the top mat and your art. A bigger reveal makes a bolder color band; a smaller one is subtle.

Bottom-weighting

Making the bottom border deliberately wider than the top so the picture sits at the optical center, which is slightly above the geometric center. Without it, a perfectly even mat can look faintly bottom-heavy. Our bottom-weighting guide explains how much to add.

Gutter

The strip of mat between two adjacent windows on a multi-opening mat — the spacing that keeps neighboring photos apart. It's the matting cousin of a border, just sitting in the middle of the board rather than at the edge.

Cutting and mounting

Multi-opening / collage / multi-aperture mat

One mat with several windows for a group of photos. "Multi-opening" and "collage" are the US terms; "multi-aperture" is the British one. The windows are separated by gutters and you cut them all from a single board. Lay one out in the multi-opening mat calculator.

Float mount

A float mount holds the artwork so the paper edge remains visible inside the frame instead of being covered by a mat opening. It is useful for deckled papers, torn edges and pieces where the edge is part of the art.

Fillet

A small decorative moulding set just inside the opening, between the mat and the artwork. Think of it as a tiny inner frame — often gilded — that adds a fine detail line. Pronounced "fill-it", framing-trade style.

Spacer

A thin strip that holds the glazing off the artwork (or off the mat) to stop them touching. Spacers matter when you frame without a mat, or want a deep shadow-box look.

Foxing, acid-free & conservation matting

Foxing is the brown spotting that appears on paper attacked by acid and damp. To prevent it, use acid-free board, or go further with conservation (archival, museum) matting — buffered, lignin-free boards that won't yellow your art over the years.

Sizes and the frame

The two size words people trip over are the mat outside and the frame size — and the happy news is they're essentially the same number. Here's the chain of arithmetic that links them.

Mat outside size

The overall dimensions of the finished mat, opening plus all four borders: mat outside = opening + borders. This is the size that has to fit inside your frame.

Frame size / rabbet / rebate

Frames are sold by the size they hold — the inside dimension, set by the rabbet (UK: rebate), the L-shaped lip that grips the mat, glass and backing. So the frame size you buy ≈ your mat outside size, not the frame's outer edge. Work it out in the frame size calculator.

Glazing

The clear sheet over the artwork — glass or acrylic (Perspex/plexiglass). It's cut a touch smaller than the rabbet so it drops in. UV-filtering glazing protects against fading.

Backing board

The stiff board behind everything that supports the artwork and fills the frame to the back. Like the glass, it's cut a hair under the rabbet size. Use acid-free backing for anything you care about.

A worked example you can re-use

Put the chain together with real numbers. An 8×10″ print with a ¼″ overlap and 2″ borders gives a 7½ × 9½″ opening (8 − 2 × ¼ = 7½; 10 − 2 × ¼ = 9½) and an 11½ × 13½″ mat outside (7½ + 2 + 2 = 11½; 9½ + 2 + 2 = 13½) — which is exactly the frame size you buy. To measure your own art before you cut, follow the how-to-measure-for-a-mat guide.

Dialect — US vs UK/AU vs Europe

Same parts, different passports. Here's the quick translation for the words that change most between an American, a British or Australian, and a French or German order form.

Passe-partout / Passepartout (FR/DE)

The French and German name for a window mat. The French hyphenate it (passe-partout); German writes it as one capitalised noun (Passepartout). It means the whole cut board, not just the window — so it maps onto "mat" or "mount", not "opening".

Common mistakes

• Confusing the opening with the art size. The window is smaller than the print by the overlap. Cut the opening to the full art size and your picture will slip straight through it.
• Assuming "mount" means the same everywhere. In the US "mounting" is fixing artwork down to a backing; in the UK the "mount" is the mat itself. An American reading a British order form can badly misread it.
• Treating mat outside as the frame's outside size. Mat outside equals the frame's inside (the rabbet), not its outer edge. Buy a frame by its inner dimension or your mat won't fit.

Keep this page bookmarked when you're filling in a custom-framing form — and when you're ready to turn the words into numbers, the mat border calculator and multi-opening mat calculator do the arithmetic for you.