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On Mats, Part Two: The Importance Of Using Archival Boards

A client recently brought me a frame to refurbish. The piece was an antique print and, although the frame itself was a bit chipped in places and not of the same vintage, it had some sentimental value for her family so they wanted to keep it. The print inside had come loose and initially she brought it in simply to have it remounted, but it quickly became obvious the mat would need to be replaced as well.

An antique print removed from its frame to reveal damage caused by outgassing from the mat

Like those in most frames from this era, the core of the mat was made from wood pulp, which is highly acidic. Over time, the core of the mat reacted with the limited amount of air inside the frame, causing it to become discoloured. The inner yellow line clearly visible in the picture above is not a decorative device; it is the bevel on the mat, which would originally have been white.

Worse though, the acids from the mat core had migrated over time to the print itself, creating a distinct burn line at the edge of the mat, as can be seen in the picture below.

Acids from the wood-pulp core of the mat have created a distinct burn line on the artwork

This is known as acid burn or mat burn and it can occur within just a few years unless acid-free boards are used. Indeed, the standards of conservation framing demand that all materials used in the interior of the frame be acid-free.

It is also apparent in the picture above that the damage extends inward toward the centre of the frame. This is obviously not caused by direct contact with the mat board but rather via a phenomenon known as outgassing, whereby gases are released from the mat core during the oxidation process. Outgassing can be a far more serious problem due to a rather unfortunate confluence of factors known collectively as "the picture frame effect". In short, the pollutants created by the oxidation of the mat board are trapped inside the narrow space between the artwork and the glass. As they build up over time, they can further react with the materials of the artwork itself or with small amounts of moisture inside the frame. This, in turn, can create new pollutants and so on and so on. It is difficult to predict or determine the exact nature of the damage this can cause as it is highly dependent upon the materials inside the frame. The discolouration to the print in the picture below is quite removed from the mat line and may be the result of moisture or secondary pollutants exacerbated by the picture frame effect.

It is difficult to predict or determine the damage which may result from "the picture frame effect"

Fortunately, acidic wood-pulp mat boards are less common these days, though they are still used in cheap frames, particularly those which have been mass produced. However, although you will often see the words "acid-free" used in conjunction with mat boards, that does not mean they are necessarily to conservation standard. Most acid-free mat boards have been pH buffered, which means they are made from the same old wood-pulp but have had calcium or magnesium carbonate added to neutralise the acids. But while they may be of a neutral pH, they still contain lignin, which is another potentially harmful pollutant. These mats have a lifespan of about 10 years, whereas true conservation-grade mat boards have a lifespan of over 50 and up to 200 years.

My standard mat boards are from the Artique Conservation range, which are made from 100% virgin alpha cellulose fibres. Despite being naturally acid and lignin free, these boards are buffered with calcium carbonate, which means they can actually absorb any additional pollutants inside the frame that might arise as a result of outgassing from the moulding or from the artwork itself. Artique boards come in over 170 different colours and are not much more expensive than buffered boards. Although they meet the standards required for conservation framing and are ideal for most framing applications, if a piece requires museum-grade protection I can supply cotton rag mats.

A new conservation-grade mat and 99% UV resistant glass should protect this print for another lifetime

The patches of discolouration made it impossible to match the paper tone exactly, but I found a tone which harmonised with the overall look of the piece, imperfections and all. The new mat was cut slightly small than the original to try to cover the worst of the burn lines, but the text at the bottom of the print didn't leave a lot of room to work with. I replicated the look of the original mat by adding a gold French line to border the window and replaced the glass in the original frame with 99% UV resistant Conservation Clear. Although the damage caused by the old mat cannot be repaired, bringing the frame up to conservation standard will protect and preserve this antique print for another lifetime.

If you have any antique pieces or vintage frames, you should consider having them refurbished with conservation-grade materials, particularly if you see any discolouration to the mat core. The cost of refurbishing a frame is insignificant compared to the prospect of damaging a piece of art or an old photograph which is potentially irreplaceable. Email me today for a quote.

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