Most framing decisions look identical the day the work comes back from the shop. A conservation-mounted print and a standard-mounted print hang on the same wall, catch the same light, and draw the same compliments. The difference is invisible at first — which is precisely why it is so easy to skip. What you are really deciding when you choose conservation mounting is what the work looks like in fifteen years, not fifteen days. That gap between present appearance and future condition is where the entire argument lives, and it is worth understanding concretely before you commit either way.
What 'acid-free' actually means in practice ¶
Paper and board are made from cellulose fibres. When those fibres break down — through oxidation, humidity, or contact with lignin, the organic compound left over from wood pulp processing — they release acidic byproducts. Those acids migrate. A standard mounting board pressed against a watercolour for a decade will transfer its acidity directly into the paper of the work, yellowing it from the back outward. Acid-free boards are buffered, typically with calcium carbonate, to a pH of 7 or above. The buffer does not last forever — it depletes over time — but a quality conservation board from a supplier like Crescent or Bainbridge will hold its pH for several decades under normal conditions. The term 'acid-free' alone is not sufficient; you also want to see 'buffered' and, for works on paper, 'lignin-free' on the specification. Lignin-free matters because lignin continues to oxidise even after acid is neutralised.
The mat board and its role as a physical barrier ¶
The mat board serves two purposes that are easy to conflate. The first is aesthetic: it provides the visual margin between the art and the frame rebate, controlling how the eye enters the composition. The second is structural: it holds the glazing away from the surface of the work. Glass or acrylic pressed directly against a photograph or a drawing creates a microclimate. Humidity condenses, mould develops, and in the case of photographs the emulsion can physically adhere to the glazing surface. A 4-ply mat — roughly 1.4 mm thick — creates enough separation to prevent that contact. For oversized prints or works with raised media like pastels or heavily worked gouache, a double mat or a spacer behind the rebate is the correct answer. The material cost difference between conservation mat board and standard mat board, on a typical A2 opening, is modest. The labour cost is identical.
Reversible hinges: the principle and the materials ¶
A reversible hinge is one that can be removed from the work without damaging it. That requirement shapes every material choice. Japanese tissue — a long-fibre paper made from kozo or gampi — is the hinge material used across most conservation-grade framing. It tears cleanly under tension, which is a safety feature: if the mounted work falls or shifts, the hinge fails before the paper of the work does. The adhesive used with Japanese tissue is wheat starch paste. It is water-soluble, has a neutral pH, and can be released with a damp brush by a conservator decades later. What you want to avoid is pressure-sensitive tape, including products marketed as 'archival tape.' The adhesive on those products migrates into the paper fibres over time, yellows, and becomes effectively irreversible. We see it consistently on works that come in for re-framing: a brown ghost line at the top edge where the tape sat. That line is permanent.
Backing boards and the rear of the frame ¶
The front of a framed work gets most of the attention, but the rear matters equally. A standard backing board — the thin grey card that ships with most frame mouldings — is made from wood pulp board with no buffering and significant lignin content. Acid migration from a backing board travels through the mount, through the mat window, and into the work over time. Conservation framing uses a 4-ply or 8-ply museum board at the rear, or in some workshops a corrugated conservation board for larger works where rigidity matters. Behind that, the frame is sealed with a paper dust cover adhered to the back of the moulding. That seal does two things: it limits the exchange of air and humidity between the frame's interior and the room, and it prevents insects from entering through the gap between the backing and the rabbet. The dust cover should be a buffered paper, not the standard brown kraft that most framers default to.
When standard mounting is a reasonable choice ¶
Conservation framing is not the correct answer for every situation, and saying so is part of giving honest advice. A reproduction poster bought for a rented flat, a child's drawing framed for the kitchen, a promotional print that will be replaced in a year: for these, standard mounting is proportionate. The distinction we apply at Frame & Canvas is roughly this — if the work is original, has sentimental value that cannot be replaced, or has any market value, conservation mounting is the appropriate baseline. If it is a reproduction with no scarcity and low replacement cost, standard mounting is a defensible choice. The honest version of this conversation is about the work itself and the owner's expectations, not about upselling a service tier.
Glazing: where UV protection fits into the system ¶
Conservation mounting addresses chemical and physical damage from the interior of the frame. Glazing addresses photochemical damage from outside it. Standard float glass transmits roughly 65 to 70 percent of ultraviolet light. UV is the primary driver of fading in works on paper, textiles, and photographs — it breaks molecular bonds in dyes and pigments directly. Museum-grade glazing, whether glass or acrylic, blocks 99 percent of UV transmission and typically sits in a visible light transmission range of 85 to 92 percent. Tru Vue Museum Glass and their Conservation Reflection Control glass are the two products we use most frequently at Frame & Canvas; both are made in the US and available through our supplier network. Combining UV-filtering glazing with conservation mounting gives you a closed system: the interior chemistry is stabilised by the board and hinge materials, and the exterior light damage is largely blocked by the glazing.
What to ask your framer before you commit ¶
Three questions will tell you most of what you need to know. First: what board are you using, and is it buffered and lignin-free? A framer doing conservation work should be able to name the board manufacturer and the product line without hesitation. Second: what adhesive are you using on the hinges? The answer should be wheat starch paste or a reversible methylcellulose. If the answer is any kind of tape, ask to see the product specification before proceeding. Third: will the glazing block UV? Ask for the UV transmission percentage, not just the product name. These are not difficult questions and they should not produce defensive responses. A framer who knows their materials will answer them quickly. The answers will tell you whether what is being described as conservation framing actually meets the standard, or whether the term is being used loosely.
Conservation mounting is not a luxury tier with diminishing returns. It is the baseline for any work you intend to keep. The cost difference over standard framing is real but modest; the difference in condition after twenty years is neither modest nor reversible. Frame & Canvas, London, frames to conservation standard as a default. The work you bring us is treated as if it matters, because it does.