A slab is two things wearing one body: a sealed shell that keeps the world off the card, and a clear window you look through. Take a card out of that shell — or never put it in one — and a shop frame does only the second half. Built properly, a framed raw card is fine for decades. Built the ordinary way, it is stuck to the glass by the end of one damp winter.
▸ THE QUICK VERSION
Nothing touches the glazing. Two to three millimetres of air is plenty; zero is the mistake that takes the card's surface with it.
Nothing adhesive touches the card. It is held by geometry — inert corners, or a well cut to its size.
Measure the rebate before you buy the frame. That lip's depth is the whole budget, and a shallow one cannot hold a safe stack.
Everything in contact is acid-free and lignin-free — mat, mount, backing, sleeve.
The frame has to do the slab's job too
NOTHING IN HERE IS SEALED BY DEFAULT
A slab does four separate things: it suspends the card at its edges with air around it, keeps fingers and dust off, survives a knock, and buffers it against the room's damp. What it does not do is filter light — the sub-chapter above this guide makes that its whole argument, and it is the one job a picture frame is glad to take on.
So framing a raw card is not a lesser version of slabbing it. It is the same problem, assembled by you, from parts a framer sells for prints. Read the drawing below from the front downwards: every layer in it is doing one of the jobs the shell used to do alone.
◆ FIGURE 1 · THE STACK IN SECTION, FRONT OF THE FRAME AT THE TOP
DRAG THE SECTION SIDEWAYS — THE 01–06 KEY SITS OFF TO THE RIGHT →
The rebate
The lip everything sits behind — framers in the United States call it the rabbet.
Glazing
Glass or acrylic. The only layer here sold with a published performance number on it.
The air gap
Nothing at all, held open by the mat's thickness or a spacer strip inside the rebate.
The card
Sleeved in polypropylene or polyethylene, never PVC. Its outer few millimetres sit under the bevel.
Mount board
Conservation board, with a well cut to the card's outline if you are sink-mounting.
Backing and dust seal
A rigid board, then archival tape around all four edges onto the frame.
The air gap is the rule with no exception
WHY GLASS AND CARD MUST NEVER MEET
Glass runs colder than the room. On a cold morning the inside face of the glazing is the first surface in the frame to reach dew point, and moisture forms there as a film you never see. A card resting against that film does what a photograph does pressed to glass: the coating softens, then dries bonded to it. Framers call that ferrotyping. It ends one of two ways — the card stays on the glass forever, or you take its top layer off getting it back.
The gap that prevents it is tiny. A single conservation mat is thin but real; a double mat, or a spacer strip hidden inside the rebate, buys the rest at no visual cost. What you must not accept is the shop frame that arrives as glass, print and grey board pressed together by six metal tabs. That is not a frame. That is a clamp.
The most valuable layer in the frame is the one that is not there — two millimetres of nothing, holding the card off the glass.
Inert in contact, reversible in method
NO ADHESIVE TOUCHES THE CARD. EVER.
One rule about materials, one about method. The materials rule: everything touching the card is acid-free and lignin-free. Ordinary wood-pulp mat board is neither, and it prints its own edge onto whatever it touches — the brown line along the window of a 1980s print is called mat burn, and it does not come out. The grey chipboard in a shop frame is usually the most acidic object in the package. If the card stays sleeved, and it should, make that sleeve polypropylene or polyethylene. What PVC does over years is the business of binders and boxes; inside a sealed frame it does it faster, because the plasticiser has nowhere to go.
The method rule is simpler still: everything you do must undo.
Polyester corners
Inert film corners — Mylar is the familiar trade name — fixed to the mount board, never to the card.
A sink mount
A well cut to the card's outline and thickness, so the mat above holds it flush. Nothing is attached to anything.
Tape, glue, hinges
Every adhesive migrates and stains eventually. Removing one takes solvent or heat, and both take surface with them.
Dry mounting
Heat plus permanent adhesive across the whole back. Irreversible by design, in a single press.
Trimming to fit
Cut the window, never the card. Board is cheap; a trimmed card is worth a fraction of the one you started with.
Spend the rebate before you buy the frame
DEPTH IS THE BUDGET, AND IT IS SMALL
Everything above has to fit behind one lip, and most ready-made frames are shallower than people expect. Price the stack in millimetres in the shop, with a ruler in the rebate, not at home with the parts already cut.
◆ FIGURE 2 · ONE 12 MM REBATE, SPENT LAYER BY LAYER
DRAG THE BAR SIDEWAYS — THE SCALE RUNS ON TO 14 MM →
Glazing buys you one band of the spectrum
WHAT 97 PER CENT ACTUALLY COVERS
Framers sell three glazings. Standard glass and acrylic block some ultraviolet as a side effect of being glass and acrylic. Conservation grade is the one with a threshold behind it: under the framing trade's own guidelines, glazing may only be sold as UV protection if it blocks at least 97 per cent of ultraviolet in the 300 to 380 nanometre range, and the better products reach 99. Museum grade adds an anti-reflective coating — a viewing upgrade, not a preservation one.
Buy the conservation grade, then stop believing it rescued you. The Canadian Conservation Institute is blunt: ultraviolet and visible light both cause fading, and it is a mistake to assume that removing the ultraviolet stops the damage. Broadly, ultraviolet does more of the work of embrittling paper, while visible light does more of the fading. Your glazing removed the invisible band; the band that lights the room is still landing on the card, which is why the guide on light dose matters as much here as it does for a slab.
One thing that never comes up at the counter: in UV-filtering plastics and films the filter is not permanent. CCI puts the general working life of those filters at about ten years. If the plan is to hang it and forget it, glass carries its filter longer than film does.
A frame is not an argument against fading. It is a way of choosing how slowly.
Close it, hang it, and leave the margin alone
THE LAST FOUR DECISIONS
- Build it in the driest room you have, on a dry day. A sealed frame preserves whatever humidity you shut inside it, for years.
- Close the back properly. Rigid board, then archival tape around all four edges onto the frame. That dust seal keeps out dust and insects, slows humidity swings, and makes opening the frame a deliberate act.
- Hang it on an interior wall. Out of any beam of direct sun, away from a radiator, away from a bathroom door.
- Leave the hidden margin alone. The strip under the mat's bevel never sees light, so in ten years it is still the colour the whole card used to be. That strip is your control sample.
The two-minute test before you close it
TAKE IT APART IN YOUR HEAD FIRST
Stand over the open frame and disassemble it mentally. If getting the card out again means peeling, soaking, heating or cutting anything at all, the frame is not safe, and no amount of expensive glass fixes that. Corners release. Sink mounts lift. Dust-seal tape is on the frame, never on the card.
Do it that way and a raw card comes out in ten years looking exactly as it went in — minus whatever light you chose to spend on it. That is the one bill this part of the hobby always sends, and the craft is in deciding how small it is.
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