Framing a Painting – Canadian Conservation Institute (CCI) Notes 10/8

Increasing the width of the rabbet

The width of the rabbet can be increased by carefully using hand tools (e.g. chisel, side-rabbet plane or router with a guide ring). It is best if the work is done by someone familiar with these tools. Working with tools near the frame’s thin rabbet must be done cautiously and without applying so much pressure that the thin face of the rabbet splits or its decorative coatings chip. Figures 2a, 2b and 2c describe one method of increasing the width of the rabbet.

Increasing the depth of the rabbet

The depth of the rabbet can be increased by adding wood strips attached with glue or with wood screws to the back of the frame (Figures 3a, 3b and 3c). If increasing the depth of the frame, add wood strips that are thick enough to be flush with the back of the auxiliary support.

Decreasing the width of the rabbet

If the frame opening is slightly too large for the painting, fill a space larger than 3 mm (1/8 in.) with small strips of a stable foam (e.g. Ethafoam, Volara) or a piece of cork to prevent the painting from shifting in the frame. These materials are compressible and will permit some expansion of the wood when RH rises. It is not necessary to extend these strips the entire length of the rabbet. Attach the strips to the side of the rabbet with white glue or double-sided tape to keep them in place.

Padding the rabbet

It is very important to prevent the paint surface from coming into direct contact with the frame’s rabbet so that the painting’s front edges are not damaged. If edge-strips are not present or are not appropriate, pad the frame’s rabbet. Padding the rabbet is often the most appropriate option as long as there is no raised impasto along the painting’s edges and the paint in contact with the rabbet can withstand some contact and pressure without crushing or breaking. Padding the rabbet should be done after confirming the fit of the painting in its frame and after making any necessary modifications to the frame.

Various materials are suitable for padding the rabbet to prevent abrasion to the painting’s surface. A colourfast, nylon velvet ribbon or synthetic felt can be attached to the rabbet using white glue. Some closed-cell, crosslinked polyethylene foams with integral skins (uncut surfaces) (e.g. Volara) would also be suitable and would provide a smooth, “slippery” surface that the painting can rest on without snagging. Foams having dimensions of 1 cm (25/64 in.) wide by 1.5 mm (1/16 in.) thick or 1.5 cm (19/32 in.) wide by 3 mm (3/32 in.) thick are useful and can be easily cut to the desired width of the rabbet. The foams can be attached to the rabbet using white glue, preferably acrylic, or double-sided tape. Double-sided tape must be stable, of high quality and possess a high tack. Ensure that continuous and strong adhesion can be achieved between either the ribbon, felt or foam and the rabbet’s wood surface. Ensure that the padding is thick enough to provide slight cushioning of the paint surface and is wide enough to cover the width of the rabbet but not be visible from the front when viewing the framed painting (Figure 4). Dark-coloured padding is much less visible along the edges of the painting than lighter colours.

If attaching the padding with glue, wait 24 hours before placing the painting in the frame to allow the glue to dry completely and the volatile compounds from the glue to dissipate.

Synthetic felts, with an acrylic pressure-sensitive adhesive on one side, can also be used as a padding or cushioning material. When ordering such products, specify that you need an acrylic or polyester felt and that a stable acrylic adhesive has been used. Fine-celled, crosslinked, closed-cell foams with integral skins (uncut slippery surface) (e.g. Volara) that have a stable acrylic adhesive are also suitable. Products with natural rubber adhesives may not be suitable to use near a paint surface. Manufacturers can change their product formulation; therefore, it is difficult to recommend a specific product. It is best to work with a supplier or manufacturer who can state with certainty the product’s composition and who understands and respects that only a stable product must be used near an artwork.

Edge-strips

When used with a frame, edge-strips which extend above the surface of the painting will prevent the frame rabbet from damaging the fragile paint surface, particularly if there is fragile impasto around the edges (Figure 5). For a painting that is meant to be framed and for which a permanent frame is not yet available, adding edge-strips to the tacking edges of the auxiliary support (stretcher or strainer) can help protect a frayed tacking margin. They also prevent damage to the painting’s edges until it is framed. The disadvantage of using edge-strips is that additional screws need to be added to the tacking margin that will pierce the canvas support. An L-shaped edge-strip, which is attached to the painting on the reverse side of the auxiliary support, rather than on the tacking margin, is a good alternative.

Materials

Strips of 3 mm (1/8 in.) thick basswood, pine or plywood, or thin aluminum moulding can be used. L-shaped wood or metal strips, attached to the reverse of the stretcher or strainer, are good alternatives. They have the advantage of not piercing the tacking margin with screws.

Use matte, non-smudging, black paint (brush or spray application) or polyurethane varnish for wood as an optional coating for the edge-strips.

Use brass or stainless steel screws, 1.5 to 1.8 cm (1/2 to 3/4 in.) long, depending on the thickness of the edge-strip, to attach the edge-strips to the auxiliary support. (The screws should not have to penetrate the wood of the auxiliary support by more than 1 to 1.2 cm [3/8 to 1/2 in.].)

Procedure

Cut strips of wood or metal to the required dimensions. These edge-strips should project 3 to 5 mm (1/8 to 1/4 in.) beyond the surface of the painting. Sand the strips to produce smooth, slightly rounded edges and corners.

When attaching edge-strips, place the painting face up upon a clean surface to determine the placement of the points of attachment. With the painting placed face up, the edge-strip will automatically be flush with the back of the painting. Ensure the points of attachment do not interfere with tacks or staples along the edges. Away from the painting, pre-drill and, if possible, countersink holes in the edge-strips. Keep the number of holes to a minimum, but use enough attachment points to prevent the strips from bowing outward.

Brush or spray the edge-strips with the desired coating. Wait a few days to allow the coating to dry completely.

Attach edge-strips to the painting’s tacking edges using brass or stainless steel screws. Pierce the canvas with an awl, through the pre-drilled holes, before inserting the screws. (An L-shaped edge-strip, attached to the painting on the back of the auxiliary support, is an excellent alternative. This would avoid having to pierce additional holes in the tacking edges.)

Glazing

If glazing is used, never permit the glass or acrylic sheet to touch the paint surface. The framing method must include a spacer to hold the glazing away from the paint surface (Figures 9a, 9b, 9c, 10 and 13).

Glazing provides additional protection from accidental damage and also some air-tightness, which reduces the effects of dirt, dust, air pollutants and environmental fluctuations. Glazing is sometimes warranted for paintings with particularly fragile surfaces or for paintings that are particularly sensitive to RH fluctuations, e.g. that have a history of lifting, flaking paint. Glazing, in addition to a sealed backing board to create a sealed enclosure, may be warranted if there is the risk that the RH could fall below 30% (Michalski 2004).

Glass is readily available and will not scratch easily, but it is heavy and prone to breaking. For this reason, a clear acrylic sheet, which is less prone to breaking than glass, may be the best glazing material for a painting that will travel. Acrylic sheet, however, should not be used for objects with a powdery surface, such as pastel or chalk. Acrylic sheet may cause an electrostatic charge to build up, which may attract loose particles to the acrylic.

Glass or acrylic sheet, treated with an optical coating to reduce reflections, is available. Such glazing materials are nearly invisible from a normal viewing distance. Museum glazing materials with ultraviolet (UV) filters are available (consult CCI Note 11/3 Glazing Materials for Framing Works on Paper). This protection, and expense, may not be required if UV radiation in the display area has been eliminated or controlled at the source to below 75 μW/lm (consult CCI Notes 2/1 Ultraviolet Filters and 10/4 Environmental and Display Guidelines for Paintings). Laminated glass, which provides protection from breakage, is available with excellent optical qualities from specialty suppliers, however at a high cost. Contact a local gallery, framing shop or the Canadian Conservation Institute for information on suppliers.

To incorporate glazing, the frame must be strong and rigid and the surface of the rabbet, against which the glazing will be placed, must be level. Place the glazing in the frame. It should not fit tightly or it may break in response to movement of the wood with handling or RH fluctuations. As a general guideline, leave 3 mm (1/8 in.) between the glazing and all edges of the rabbet. However, frames with wood moldings wider than 10 cm (approximately 4 in.) may need more space. Place an inner wood frame, attached at its corners, against the glazing to act as a spacer between the glazing and the paint surface (Figures 9a, 9b and 9c). Alternatively, attach padded wood spacer strips to the glazing (Figure 10). The depth of the space, between the paint surface and glazing, will depend on the size, rigidity and nature of the painting’s surface as well as on the type of glazing used. Acrylic glazing, which has some flex, may require more space. Suppliers of glazing materials for artworks should be able to offer information on the space required. (The depth of the space could vary between 7 mm [1/4 in.] to 6.4 cm [2 1/2 in.] for small to moderately large paintings.) Pad this inner frame where it touches the paint surface, using the procedure described in the section Padding the rabbet.

A thin padding between the glazing and the wood rabbet may also be required, particularly if the wood surfaces are rough. Similar materials to those recommended for padding the rabbet can be used.

Hanging devices

Attach a suitable hanging device to the frame (consult CCI Note 10/4 Environmental and Display Guidelines for Paintings).

Wood panels and rigid hardboards

Many panel paintings—particularly those with pronounced warps or curvatures, or panels that are very large—require framing methods tailored to their needs. In these cases, contact a conservator for advice. Undistorted wood panels and hardboards, such as Masonite, also require special framing procedures that accommodate their size, weight and dimensional changes when RH fluctuates.

It is extremely important to provide space in the frame so that wood panels or hardboards can expand during periods of high RH. For the same reason, nothing should be attached to the panel itself. Failure to allow some movement of the wood or hardboard support can cause the painted panel to warp or split as the wood responds to RH fluctuations.

How the painting will fit in the frame depends on the time of year and, in particular, on the RH conditions when the framing is done. If the painting is framed when the RH is at a maximum, a minimum of space is required between the side of the rabbet and the work of art (3 to 6 mm or 1/8 to 1/4 in.). If the framing is done during a period of low RH, allow enough space for wood components to swell during periods of high RH. Use the numbers below as a guide (Table 1).

Hardboard can change as much as 0.5% in length and in width during a 50% change in RH. Thus, when framing hardboards of 60 to 120 cm (approximately 2 to 4 ft.), to be safe, allow a 3 to 6 mm space (1/8 to 1/4 in.) on each side between the edge of the rabbet and the work of art.

Solid wood panels can change in dimension up to 3% of the total width with a 50% RH change. The greatest change in dimension will occur perpendicular to the grain of the wood. The space required to permit unrestricted expansion of the wood across the grain during periods of high RH depends on the size of the panel. A panel painting 1 m by 1 m (approx. 3 ft. by 3 ft.) will require 1.5 cm (9/16 in.) of space on each side parallel to the panel’s wood grain. Similarly, a panel painting of 0.5 m by 0.5 m (18 in. by 18 in.) could expand by 1.5 cm (9/16 in.) and will, therefore, require 0.75 cm (9/32 in.) on each side parallel to the wood grain. However, as there will be no space between the painting and the bottom rabbet edge, allow for all the space in this direction to be between the top of the panel and the top rabbet edge.

If the painting tends to shift within this space, a compressible material, such as Ethafoam, could be used to loosely fill the space. Wood panel and hardboard supports may warp due to RH fluctuations. Therefore, when glazing is incorporated into a frame, it is important to provide enough clearance between the painted panel and the glazing to prevent the two from touching should warping occur.

Pad the frame’s rabbet using the procedure described previously.

For small to moderate-sized panels or hardboard, place the painted panel in the frame, followed by a layer of 4-ply matboard. The matboard will help buffer fluctuations in RH. Layers of corrugated plastic sheet (e.g. Coroplast) cut to the size of the painting can be added until the level is flush with the back of the frame. Cut a final, rigid, supporting backing board of wood, hardboard or Plexiglas so that it extends over (or onto) the back of the frame (Figure 13). The backing board will hold the painting in the frame and will seal the painting against dust and dirt. For small, lightweight panels no larger than 0.5 m by 0.5 m (18 in. by 18 in.), a corrugated plastic sheet or a stable, heavy-duty foam board (e.g. Gatorfoam) may be enough of a supporting backing board.

Alternatively, the backing board can be inserted after the layer(s) of matboard such that the backing board is flush with the back of the frame. Frame-sealing tape can be used to create a seal between the backing board and the frame (Figure 14).

Hold the backing board in place with brass mending plates. Bend the mending plates as necessary. When possible, use two screws to attach each plate to the frame only. The rigid backing board should gently hold the painted panel in place (Figures 13 and 14).

Large, heavy panels may require a stronger attachment.

Paintings on rigid card

Paintings on card supports should not be tightly wedged in the frame. Allow a 3 to 6 mm (1/8 to 1/4 in.) space on all sides between the rabbet edge and the work of art.

Pad the frame’s rabbet, following the procedure described previously. Velvet ribbon, synthetic felt, foam or acid-free matboard can also be applied to the side of the rabbet to reduce rubbing on the card's edges.

Place the painting in the frame. Add one or two pieces of acid-free matboard cut to the size of the painting. Add layers of corrugated plastic sheeting until the level is flush with the back of the frame. As previously described, finish with a firm, rigid board, such as corrugated plastic sheeting or a stable, heavy duty foam board cut to overlap onto the reverse of the frame (Figure 13).

Hold the backing boards in place under gentle pressure with brass mending plates that are attached only to the frame.

Alternatively, if a rigid backing board does not overlap onto the reverse of the frame but fills the rabbet and remains flush with the back of the frame, straight mending plates, attached only to the frame, can be used to hold the layers in place. In this case, a frame-sealing tape should be used as a dust seal (Figure 14).

As an alternative, paintings on rigid card can be matted using a sink mat and can then be framed. This technique is described in Merrily Smith’s Matting and Hinging of Works of Art on Paper (consult the Further reading section).

Enclosed frame or case design

Specially designed enclosed frames or cases provide superior protection against dirt, mechanical damage, spills, air pollutants and sudden fluctuations in temperature and RH. A basic design incorporates glazing (which is held away from the paint surface) and a backing board. Both of these are sealed to the frame using methods appropriate for the situation (McKay 1990, Sozzani 1997 and Michalski 2004). To provide the greatest protection against the deteriorating effects of fluctuating environmental conditions, particularly RH, incorporate a humidity-buffering agent, such as silica gel in a suitable container, behind the painting within the enclosed frame. However, if the glazing and backing board are sealed properly to the frame, it should be possible to create an enclosure that will buffer RH fluctuations up to and including seasonal changes using little or no silica gel. Placing a 4 mm (5/16 in.) matboard buffer in a carefully sealed frame, or a silica gel pack, will provide excellent control during day–night and seasonal RH fluctuations.

An enclosed frame or case design is recommended for paintings exhibited in areas without adequate RH control. It is particularly useful for paintings on supports, such as ivory or wood, that are prone to damage resulting from the support material shrinking and swelling in response to environmental fluctuations. For more information on enclosed frame or case design, contact CCI.

Handling-travel-storage frame

An HTS frame (Figure 15), based on a design used at the National Gallery of Canada, is suitable for most paintings without frames (consult CCI Note 10/16 Wrapping a Painting). This is not a decorative frame but a functional frame for the handling, transportation and storage of the work of art.

Mending plates can be used to attach a painting to the HTS frame. If the painting is to be removed and replaced repeatedly, the screw holes may become incapable of holding the screws. Using threaded T-nut fasteners in the plywood of the HTS frame may prolong the use of the holes. Multi-purpose fasteners or hangers, such as Oz Clips or similar hangers used at the Tate galleries in England, have the advantage of being permanently attached to a painting. They are used in the closed position for display and in the open position for attaching the painting to an HTS frame. When measuring for this type of frame, allow adequate hand space between the sides of the painting and the travel frame so that the painting is easy to position, secure and remove. The sides of the frame should extend beyond the paint surface so that a protective sheet of polyethylene can be stretched across the front of the frame, without touching the paint surface.

Bibliography

Michalski, S. “Risk Analysis of Backing Boards for Paintings: Damp Climates vs. Cold Climates.” In Minimo intervento conservativo nel restauro dei dipinti, CESMAR7, Secondo congresso internazionale Colore e Conservazione, Thiene (VI), 29–30 October 2004. Saonara, Italy: Il Prato, 2004, pp. 21–27.

Further reading

Dahlin, E., ed. PROPAINT – Improved Protection of Paintings During Exhibition, Storage and Transit: Final Activity Report (PDF format). Kjeller, Norway: Norwegian Institute for Air Research, 2010.

Hackney, S. “Framing for Conservation at the Tate Gallery.” The Conservator 14,1 (1990), pp. 44–52.

McKay, H. “A Sealed Frame-Case for a Painting.” Journal of the International Institute for Conservation - Canadian Group 15 (1990), pp. 9–11.

Smith, M. Matting and Hinging of Works of Art on Paper. Washington, D.C.: Library of Congress, 1981.

Sozzani, L. “An Economical Design for a Microclimate Vitrine for Paintings Using the Picture Frame as the Primary Housing.” Journal of the American Institute for Conservation 36,2 (1997), pp. 95–107.

By the staff of the Fine Arts division
Primary author: Debra Daly Hartin
Revised by Debra Daly Hartin and reviewed by Fine Arts staff in 2018.

Originally published in 1993

Également publié en version française.

© Government of Canada, Canadian Conservation Institute, 2018

ISSN 1928-1455