Conservation Framing: Glazing, Mats and Mounts

Why framing is a conservation decision

Conservation framing treats the frame as the object's closest environment rather than as decoration. Glazing, mat, mount, backing and fixings all touch the work or share its air for years, sometimes decades, and each can protect it or slowly damage it. Poor framing is one of the most common sources of avoidable harm, particularly to works on paper.

The familiar problems are well documented: acidic mats that leave brown lines, pressure-sensitive tape that stains and turns brittle, works dry-mounted to boards so that they cannot be removed without risk, and glazing pressed directly against a surface. None of these is visible from the front until the damage has been done, which is why works acquired in older frames are worth having opened and checked.

Good framing works in the other direction. It shields a work from handling, dust, pollutants and some light, buffers it against changes in the room, and makes it safer to move. A conservator, or a framer experienced in conservation work, should be involved for anything valuable or fragile.

Glazing: UV filtering, glass and acrylic

UV-filtering glazing removes much of the ultraviolet radiation from light reaching the work, and it is widely recommended for works on paper, photographs and other light-sensitive materials. It is not a complete solution. Visible light also causes fading, so filtered glazing reduces the rate of damage rather than stopping it, and decisions about where and how long a work is displayed still matter.

Glass and acrylic each have trade-offs. Glass resists scratching and does not hold a static charge, but it is heavy, and when it breaks the shards can cut or puncture the work. Acrylic is lighter and far less likely to shatter, which makes it a common choice for large works, works in transit and homes in earthquake-prone regions, but it scratches easily and can build up static that lifts loose particles from pastel, charcoal and flaking surfaces. For those media, glass is generally preferred.

Anti-reflective coatings are available for both materials and make a considerable difference to viewing. Laminated glass holds together better if it breaks. Whichever material is chosen, the glazing should never touch the surface of the work.

Mats, spacers and air space

A mat, or window mount, does two jobs. It frames the image visually, and it holds the glazing away from the surface, leaving an air space that reduces the risk of condensation, mould and the work adhering to the glazing. Where a work is floated or shown without a mat, spacers hidden in the rebate of the frame do the same structural job.

Mat board should be conservation grade, typically made from cotton rag or purified wood pulp free of harmful acids. Boards may be buffered with an alkaline reserve or unbuffered, and some materials, including certain photographic processes, are sometimes better housed in unbuffered board. A conservator or a specialist framer can advise which suits a particular object.

Paintings on canvas are traditionally shown unglazed, but glazing can be added for protection in vulnerable settings. When it is, the frame needs enough depth for a spacer so that the glazing sits well clear of the paint.

Mounts and hinges: attaching the work reversibly

How a work is attached inside the frame is the decision most likely to cause permanent harm. The governing principle is reversibility: any attachment should be removable later without damaging the work.

For works on paper, the usual conservation approach is hinges of Japanese tissue attached with wheat starch paste, which a conservator can release with moisture. The hinges are meant to be weaker than the paper, so that if the work is stressed the hinge fails first. Where any adhesive on the work is inappropriate, photo corners or edge strips hold the sheet without anything touching its face. The following should not be used on the work itself.

Backing, sealing and fixings

The back of the frame protects the work from dust, insects and impact. A rigid conservation-grade backing board behind the mount, sealed around the edges and finished with a dust cover, is standard practice. For a canvas painting, a backboard fixed to the stretcher protects the canvas from knocks and vibration and slows the exchange of dust and moisture.

Paintings should be held in their frames with fixings that can be removed without harm, such as flexible metal plates screwed into the frame, rather than nails driven through the stretcher. The rebate of the frame, where the painting's edges rest, is often lined with a soft material to prevent abrasion of the paint along the edges. Hanging hardware should be attached to the frame rather than the stretcher, and sized for the weight.

Questions to ask a framer

Not every framer works to conservation standards, and the word archival is used loosely. A framer who answers the questions below clearly, and who will refer a fragile or damaged work to a conservator before framing it, is usually a good sign.