Mount board is the part of a frame most people don't notice — until they see a print with the wrong mount, and then they can't unsee it. The mount does more than fill space between the print and the frame. It controls the eye's path to the artwork, protects the print from glass damage, and signals whether a print is decoration or proper wall art.
What mount board actually does
Mount board (also called matt board or mat board, especially in the US) is a thick paper or card border that sits inside the frame, around the print. It has three jobs:
- Visual breathing room — separates the print from the frame so the eye reads the artwork first, not the frame.
- Physical protection — keeps the print from touching the glass. Direct contact with glass causes prints to stick over time, especially in humid rooms or bathrooms.
- Hierarchy signal — a print with a generous mount reads as gallery art; a print without a mount reads as a poster.
When to use a mount
Default: always use a mount. There are only three situations where you'd skip one.
- Edge-to-edge designs — type-led prints, posters, full-bleed photography where the image fills the entire frame is part of the design intent.
- Wall of small prints — for clusters of 6×4 or 7×5 photos in a tight grid, mounts can fragment the wall visually. No mount keeps the cluster reading as one piece.
- Frames smaller than A5 — physically there's no room for a meaningful mount.
Otherwise, mount.
How wide should the mount be?
This is the most common question and the most under-answered. Generic advice ("about 5cm") ignores the relationship between mount width, print size, and frame proportions. The right answer depends on the print size.
| Print size | Frame size | Mount width (all sides) |
|---|---|---|
| A5 | A4 | 32mm |
| A4 | A3 | 42mm |
| A3 | A2 | 60mm |
| A2 | A1 | 85mm |
| A1 | A0 | 120mm |
This scales the mount proportionally with the print. The print always reads as the focus. We cut every size to order — A4 picture mounts, A3 picture mounts, A2 picture mounts and A1 picture mounts, including an A3 mount for an A4 print.
The weighted bottom mount (advanced)
For portraits, fine art prints, and gallery-style framing, professional framers use a weighted bottom mount — the bottom margin is slightly wider than the top and sides. This compensates for an optical illusion: a print with equal margins looks bottom-heavy to the eye because the visual centre of any rectangle sits slightly above the geometric centre.
Typical weighted bottom: top and sides equal, bottom 20% wider. So if top, left and right are 50mm, bottom is 60mm.
Use weighted bottoms for hero pieces, single statement prints, and anything portrait-orientation. Skip for landscapes and grids.
Mount colour
For most prints, bright white. It maximises contrast, keeps the print as the focus, and never dates. Off-white or cream works for warm-toned prints and softer rooms but reduces contrast.
Coloured mounts (sage, navy, sand) are a strong stylistic choice — use sparingly and always pull the colour from the print itself. A sage mount on a botanical illustration with sage in the foliage looks deliberate. The same mount on an unrelated print looks arbitrary.
Black mounts are rare but work on white frames for high-key or ethereal prints. Avoid for anything else.
Single vs double mount
A double mount has two layers of card with a narrow strip of the inner colour visible (often a thin black or coloured line between the print and the main mount). This adds visual sophistication and is the standard for fine art framing.
Single mount for: posters, photography, most home framing.
Double mount for: hero pieces, fine art prints, anything where the framing itself is part of the statement.
Mount thickness
Standard mount board is 1.4mm thick. This is fine for 95% of framing. For deeper-set looks (popular for photography and modern art), use 2.5mm or stack two layers of standard board. Anything thicker requires a deeper frame rebate — check the frame depth before ordering.
Acid-free and museum grade
For prints you care about long-term, specify acid-free mount board. Standard mount board contains lignin, which yellows and breaks down over time and can transfer onto the print itself. Acid-free (also called "conservation" or "museum grade") mount costs 2–3× more but keeps prints intact for decades.
If you're framing original artwork, signed prints, photographs you want to keep, or anything irreplaceable — pay for acid-free. For decorative posters you'll swap out in five years, standard is fine.
Common mount mistakes
- Mount too narrow — print feels cramped, frame dominates.
- Mount too wide — print feels lost, frame feels empty.
- Cream mount with black frame — the contrast between cream mount and black frame fights the print.
- No bottom weight on a portrait print — the print looks like it's sinking.
- Coloured mount that doesn't appear in the print — reads as arbitrary, not designed.
Get the mount right and the frame becomes invisible. That's the goal: the eye should land on the print first, the framing second.