A window mount gives artwork a quiet margin between its edges and the frame. It also keeps the paper away from the glass, hides uneven edges when needed, and makes a small picture sit more comfortably within a standard frame. The work is mostly measuring, marking, and making clean cuts in the right order.
For a first attempt, use a spare piece of mountboard and practise the aperture cut before working on the final board. A sharp blade, a firm ruler, and patience matter more than elaborate equipment.
What you will need
- Acid-free mountboard, large enough to cover the frame opening
- A steel ruler with a clear, straight edge
- A mount cutter or sharp craft knife
- A self-healing cutting mat or other suitable cutting surface
- A pencil and a soft eraser
- Acid-free paper hinge tape or artist’s tape intended for artwork
- The artwork and frame
- A clean, flat table with good light
A dedicated mount cutter makes it easier to produce a 45-degree bevel, but a sharp craft knife can also be used with care. Ordinary household tape should not be placed on the artwork. If the piece is valuable, irreplaceable, or made with delicate watercolour or other friable media, a professional framer or conservator is the safer choice.
Photo by Neon Wang on Unsplash.
Measure the frame and artwork
Begin by measuring the frame’s rebate: the recessed opening in which the mounted board will sit. Do not rely only on the stated frame size, since small frames can vary. Measure the width and height of the opening, then check the depth available for the mount, artwork, glazing, and backing.
Cut the outside of the mountboard just fractionally smaller than the rebate. It should drop in without force, but it should not leave an obvious gap. A millimetre or two of clearance is generally more useful than a tight fit, especially where the frame or board may shift slightly with changes in humidity.
Next measure the artwork. The aperture should be slightly smaller than the sheet so the mount overlaps its edges. This prevents the picture slipping through the window and gives the eye a clean boundary. The overlap need not be large, but it must be enough to hold the artwork securely without hiding important marks, signatures, or deckled edges.
For a rectangular image, write down four measurements:
- The outside width of the mount
- The outside height of the mount
- The width of the aperture
- The height of the aperture
The simplest border calculation is:
border = (outside measurement - aperture measurement) ÷ 2
You may begin with equal borders, then adjust them by eye. Many mounts look more settled when the lower border is slightly deeper than the upper and side borders. This gives the image a little visual weight at the bottom. The difference should be modest; a strongly uneven border can appear accidental.
For a small print, a border of around 45–75 mm may feel generous, while a smaller margin may suit a compact frame. These are starting points rather than rules. Let the artwork’s proportions, tone, and intended setting guide the final decision.
Cut the mountboard to size
Place the mountboard face down on the cutting mat. Mark the outside dimensions on the reverse, keeping the lines square with the board edges. Use the steel ruler as a guide and make several light passes with the knife rather than trying to force the blade through in one stroke.
Keep your free hand behind the cutting direction, never in front of the blade. If the ruler moves, stop and reset it rather than correcting the cut halfway along. A clean, slightly slow cut is easier to achieve than a fast one made under pressure.
Check the board in the frame before cutting the window. If it is too tight, trim the outside edges now. Once the aperture has been cut, the board is more delicate and harder to handle accurately.
Mark the window on the reverse
Turn the board so its back is facing upwards. Measure from the outside edges and mark the four corners of the aperture. Join them with the steel ruler, keeping each line square. These pencil lines indicate where the cut will begin and end.
Before using the blade, look at the front of the board and imagine the artwork beneath it. Check the orientation, the intended top edge, and the position of any signature or important detail. This small pause prevents one of the most dispiriting mistakes: a neatly cut mount with the image placed too high, too low, or upside down.
If the board has a directional surface or a coloured core, mark a small registration line across one outside edge and the corresponding edge of the cut-out. This helps you return the centre section to its original position if you are testing the cut or making a double mount.
Photo by Jonathan Cosens Photography on Unsplash.
Cut the bevelled aperture
A traditional window mount has edges cut on a bevel, commonly at about 45 degrees. The bevel lets a narrow line of the board’s core catch the light and gives the window a more finished appearance than a blunt vertical cut.
Set the mount cutter according to its instructions, or use a knife held carefully against a suitable bevel guide. Work from the reverse of the board, beginning at one marked corner and ending at the next. Stop exactly at the corner mark. Do not cut beyond it to make the turn; each side should be cut as a separate straight line.
If using a craft knife, keep the ruler firmly in place and make several controlled passes. The blade should be sharp enough to cut rather than crush the board. A dull blade often produces a ragged face, torn paper fibres, or a bevel that wanders away from the line.
Cut the four sides in the same direction where practical, keeping the board still. When the final cut is complete, lift the centre gently from the back. Do not pull hard. If a small fibre remains, trim it with the blade rather than tearing it away.
Inspect the front. The bevel should be continuous, with corners meeting neatly and no visible overcuts. Tiny irregularities can sometimes be eased with a fresh blade, but large errors are difficult to disguise. This is why a practice cut on scrap board is worthwhile.
If the board has a white or pale core, the bevel may be left as it is. With a coloured board, the exposed core becomes part of the design. Keep it clean, and avoid rubbing the cut edge with your fingers, as skin oils can mark lighter surfaces.
Hinge the artwork to the mount
The artwork should usually be attached to a backing board or to the reverse of the mount with a hinge at its upper edge. The hinge allows the paper to hang naturally and helps avoid trapping the sheet flat on all four sides. Paper expands and contracts with changes in moisture; a fully fixed sheet has less room to move.
Place the mount face down and lay the artwork behind the window, adjusting it until the visible margins are even. Use small temporary pieces of low-tack tape on the outer edges of the artwork or backing board to hold the position while you prepare the hinge. Do not burnish tape onto the picture itself.
For a simple top hinge, attach a short strip of acid-free paper hinge tape to the back of the artwork near the upper edge, then attach the other half to the backing board or mount. The adhesive should touch only the hinge and the support, not the image area. Use two small hinges rather than one long strip for a modest sheet, leaving a little space between them.
A T-hinge, in which a second strip crosses the first on the support, gives extra security while keeping the attachment removable. Avoid pressing the artwork hard into place. Smooth the hinge gently and allow any adhesive to settle according to the tape manufacturer’s directions.
For particularly delicate, valuable, or moisture-sensitive work, do not improvise with wet glue. Hinging methods require appropriate materials and judgement, and conservation mounting may be necessary.
Assemble the frame
Clean the inside of the glazing before assembling the frame. Handle glass by its edges and keep the work area free of loose board fibres. Place the glazed frame face down, followed by the window mount and artwork, then the backing board.
Check the order and orientation before securing anything. The artwork should not touch the glass; the thickness of the mount creates the necessary space. If the stack is too deep for the frame, do not force the backing into place, since pressure can distort the board or mark the paper.
Secure the backing with the frame’s tabs or with suitable framing points. The contents should be held firmly enough not to rattle, but not compressed so tightly that the mount bows. Turn the frame over and inspect it under good light. Look for dust beneath the glass, a shifted artwork, uneven borders, or a corner that has lifted.
Photo by Zack Yeo on Unsplash.
Common mistakes to avoid
Cutting from the front
Marking and cutting from the front can leave pencil lines or accidental scratches on the visible surface. Work from the reverse, then inspect the face only after the aperture is free.
Using a blunt blade
A blade that drags through the board crushes the bevel and tears the paper covering. Replace or refresh the blade as soon as it begins to require force.
Making the aperture too large
A window that exactly matches the artwork can allow a corner to slip through or leave an untidy gap. Make the aperture slightly smaller and check that no important detail is hidden.
Fixing all four edges of the artwork
Four-sided taping can restrict the paper as it responds to its surroundings. For ordinary paper artwork, a properly made upper hinge is a gentler arrangement.
Ignoring the frame depth
A beautifully cut mount is of little use if the assembled layers cannot sit comfortably in the rebate. Test the empty board and check the full stack before applying hinges.
Rushing the corner cuts
Most visible faults begin where two bevels meet. Stop at each corner mark, keep the board still, and make the final part of each cut with particular care.
Finishing the piece
Erase remaining pencil marks from the reverse with a soft eraser, taking care not to rub across the bevel or disturb the hinge. Keep the finished mount flat until it is fitted. Store unused mountboard horizontally, protected from damp and direct sunlight.
A neutral off-white, warm grey, or muted tone will usually let the artwork lead. A coloured mount can work well when it quietly echoes a colour within the image, but the border should support the picture rather than compete with it. Once the proportions are measured and the cuts are deliberate, even a simple standard frame can give a modest work the calm, finished setting it deserves.