What a mount does to a print, and how wide it should be

A mount is the card border between a print and its frame, and most people treat it as decoration. Its first job is mechanical: it holds the glass off the surface of the paper so the two cannot stick together. The visual job is real as well, because a mount gives an image an edge and stops the eye sliding off into the wall. Both jobs have numbers attached, and one choice in this process, the board itself, will either preserve the print or leave a permanent brown line across it.

Mount, mat, and the words on the invoice

A mount in British usage is a mat in American usage, and both mean the same thing: a sheet of card with a window cut in it, sitting in front of the artwork. The window is cut at an angle, which is the bevel, and the pale line you see around the opening is the core of the board showing through.

Behind the print sits a second board, the backboard or undermount, which is usually the thing people skip. If the backboard is cheap grey card, it is in permanent contact with the back of the print and it will do damage whatever the front board is made of.

Double mounting means two boards stacked, with the inner one offset by a few millimetres to show a narrow line of a second colour. It is a trick worth knowing for dark artwork, because a thin dark inner line gives the image a crisp edge without reducing the pale border.

The reason that is not aesthetic

Paper and glass should never touch. Humidity cycles through the year, paper expands and contracts, and condensation can form on the inside of the glazing in a cold room. Over time an inkjet or photographic surface pressed against glass will bond to it, which shows up as glossy patches or as the print tearing when the frame is opened.

The mount is what prevents that, by being thicker than nothing. A standard 1.4 mm board gives enough air gap for most situations, and a thicker conservation board gives more.

If you want a frameless look with no visible border, you still need the gap. Framers use clear spacers that sit in the rebate, hidden behind the lip, and any decent framer will suggest them without being asked. A print held flat against glass by a clip frame is on a clock.

How wide, in actual numbers

The rule of thumb is that the mount should be clearly wider than the frame moulding, so the two do not compete. In practice: around 5 cm of border for a small print at 8 by 8 or 9 by 12 inches, 6 to 7.5 cm at 12 by 16, and 7.5 to 10 cm at 18 by 24.

Under about 3 cm a mount stops reading as a border and starts reading as a trimming error. If you are unsure, go wider. Galleries and museums err wide because a generous border tells the eye where to stop, and because the image gets more attention when it is surrounded by nothing.

Square images need proportionally more width than rectangular ones. A square border of equal width on all four sides looks narrower than the same measurement on a portrait format, so a square print like Curled wants a wider mount than its size would suggest.

The weighted bottom

Traditional framing adds 10 to 20 per cent extra to the bottom margin, so a mount with 7 cm at the sides and top might have 8 or 8.5 cm at the bottom. Two reasons are usually given: the optical centre of a rectangle sits slightly above the geometric centre, and a picture hung at eye level is seen from very slightly below.

It is a convention, not a law. On portrait format work it reads as settled and deliberate. On a square image with equal margins, nobody has ever noticed, and forcing a weighted bottom onto a square can look like the mount was cut wrong.

If you order a ready made mount it will almost certainly have equal margins, which is fine. The weighted bottom is a reason to use a framer, not a reason to reject an off the shelf mount.

The board is where the money matters

Ordinary mount board is wood pulp with a coloured surface paper and a cream core, and that core is acidic. Over roughly ten to twenty five years, faster in a warm bright room, it transfers acid into the print along the line where the bevel touches it. The result is a brown line following the window opening, and it cannot be reversed.

Framers call it mat burn, and it is the single most common avoidable damage to framed prints. Conservation grade board is buffered alpha cellulose and will not do it. Museum grade board is cotton rag, lignin free all the way through, and is the best available.

The price difference on a small mount is small enough that there is no real argument. On a print worth framing at all, ask for conservation board at minimum and specify the backboard too, because framers will sometimes upgrade the front and leave grey card behind the work.

How to attach the print, and what not to use

The correct method is hinging. Strips of acid free gummed linen tape or Japanese tissue with starch paste along the top edge only, so the paper hangs and is free to expand and contract. Polyester photo corners are even better because nothing is stuck to the artwork at all.

What not to use, in order of how often it happens: masking tape, which goes brittle and brown and leaves adhesive in the paper. Clear office tape, which yellows and bonds permanently. Dry mounting, which glues the whole sheet to a board and is irreversible. Double sided foam pads, which dent the paper from behind.

Also do not trim the border to make the print fit a frame. The white margin is part of the object, it gives the mount something to overlap, and cutting it is the one mistake that cannot be undone later.

Float mounts, and what we actually send

A float mount shows the whole sheet including its edges, sitting on top of a backing board rather than behind a window. It needs spacers so the glass clears the paper, and it only looks right when the edge is worth showing, which usually means a deckle edge or a visible plate mark.

Our prints are not made for floating. They arrive with a thin white border, which is a handling margin rather than a feature, and they are intended to go behind a window mount where that margin is hidden.

To be plain about it: the frame in the product photographs is a mockup and is not included. The Longest Night and Visitors both ship rolled in a tube, and the mount and frame are yours to choose. If you only upgrade one thing in that process, upgrade the board.

Questions people actually ask

How wide should a mount be for a print?

Around 5 cm for small prints, 6 to 7.5 cm at 12 by 16 inches and 7.5 to 10 cm at 18 by 24. The mount should be clearly wider than the frame moulding, and anything under about 3 cm starts to look like a cutting error.

Do I actually need a mount, or can the print touch the glass?

You need the gap. Paper pressed against glass through humidity cycles can bond to it, leaving glossy patches or tearing the print when the frame is opened. If you want no visible border, ask the framer for hidden spacers instead.

What is mat burn?

A permanent brown line left on a print where acidic mount board touched it, usually along the bevel of the window. It develops over ten to twenty five years and is prevented by using conservation or museum grade board front and back.

What tape should I use to mount a print?

Acid free gummed linen tape or Japanese tissue with starch paste, hinged along the top edge only, or polyester photo corners which touch nothing. Never masking tape, clear office tape, dry mounting or foam pads.

Why is the bottom margin of a mount sometimes wider?

It is a framing convention that adds 10 to 20 per cent to the bottom, because the optical centre of a rectangle sits above the geometric centre and pictures are seen slightly from below. It suits portrait formats and is unnecessary on squares.