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  • Polyethylene foam as a frame-padding material for wood panels?ApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2019-01-17 15:25:23 ... Most recent comment 2019-01-19 18:37:32
    Matting, Framing, and Glazing Rigid Supports Oil Paint Art Conservation Topics

    ​I've been trying to come up with a better way to frame oil paintings on (solid, uncradled) wood panels. My current thought is: 

    1. Construct the frame to allow for the appropriate amount of room for expansion within the rabbet. Fill the voids on the sides of the panel with a polyethylene foam (e.g. EthaFoam, Volara, Cellu-Cushion). 

    2. Cut a large piece of polyethylene foam to fit behind the panel, filling the rabbet flush to the back of the frame.

    3. Screw a piece of 1/8" plywood to the back of the frame to hold everything in place. 

    Basically the panel would be surrounded, sides and back, with foam that would hold it firmly in place and keep it centered in the frame, while also not restraining the panel, so that it can move in response to changes in humidity. 

    Is this a sound approach? Is a polyethylene foam material like EthaFoam a good material for this application? 



Answers and Comments

  • EditDeleteModerator Answer

    I will send this to a few experts in the area but as at least one is furloughed at the moment, I will add a few remarks of my own. I hope that someone with greater expertise will weigh in soon.

    Probably what you proposed would work perfectly well for a new painting. However, there are a few considerations to keep in mind when framing or reframing a solid wooden panel. One is to slow the rate at which he panel experiences changes in RH. Museums even go so far as to place the panel within an enclosed envelope. This may be to either maintain (“lock-in”) the humidity conditions when the envelope was created (this is certainly complicated by the fact that RH percentages change with shifts in temperature). A more sophisticated system involves the inclusion of a buffering material (eg silica gel) within the panel envelop. The gel absorbs and releases moisture in response to temperature changes to help maintain a stable RH. This is optimal but entirely impractical for most individuals and galleries.

    Another consideration (which you clearly have thought of) is to make sure that a nonabrasive material is placed/adhered to any part of the frame where the panel touches. Felt has often been used within the rabbet of frames for canvas and wooden panel paintings but would be unappropriated for other objects (eg sulfur in the felt acting on a copper panel, etc). Volara is a reasonable alternative.

    It is also important to not overly restrain the movement of the panel. With changes of RH, wood expands and contracts across the grain (90 degrees to the grain lines. That means that a panel with vertical grain changes dimensions and bows far greater in the horizontal direction that in the vertical direction. In such a situation, we would want to have most of the force holding the panel in the frame at center of the top and bottom of the panel and very little at the left and right edges where the most dimensional change would occur.

    Brian Baade
    2019-01-18 17:53:01
  • EditDeleteModerator Answer


    A critical factor, here, is what type of panel this is, pressed wood, laminated wood, or solid board, since each will have differing expansion/contraction coefficients.  If it is a solid board, it must be given room to expand across the grain and should be secured at the top and bottom of its grain center, only. That allows it to move, along its outsides, and reduces its chance of cracking. If it is laminated wood, it should be less likely to warp and even spacing all around makes sense. The same is true for pressed wood, but attention should be paid to ensure that its edges (especially its corners) are protected from physical insult, as they can be quite vulnerable.  Volara between the panel’s edges and the frame rabbet, both rabbet width and depth, is a great idea and Volara between the back of the panel and a backing board is also a good idea. The backing board can be made of Vivak (PETG) sheet 00.09” or thicker, which can be screwed into the back of the frame and which will be lighter than plywood and will allow one to see into the back of the frame, to monitor conditions, there.  In short, the plan you describe should work well, for all but solid boards.

    All best,

    Hugh Phibbs


    2019-01-19 13:50:10
  • ApproveRejectUn-ApproveUser Comment

    ​A bit more context:

    The panels are solid wood--in this particular case, quarter-sawn black walnut, though in the past I have also used panels made from white oak, Honduran mahogany, and poplar (I no longer use poplar, as it tends to be less stable, and also quite a bit softer, than those other woods). 

    I do understand that the wood needs room to expand in the frame, particularly across the grain (along the grain, it barely moves at all). I factor in expansion when sizing frames using species-specific wood movement calculators, which you can find in a number of places online. Woodworkers use them when fitting panels into paneled door frames or cabinet doors, since if the panels aren't left with sufficient room to expand in the frame, they will crack. 

    The panels I'm working with now, I've planed a bit thinner than what I've used in the past--partly to reduce weight, and partly because I've observed that when working with quarter-sawn, straight-grained wood of a relatively stable species, even 1/4"-thick panels aren't likely to warp much. I should also note that I work pretty small--the panel I am prepping today, for example, is 6 inches by 7 inches. 

    Anyway, I have used offset clips to fix wood panels in frames in the past, in the manner explained above (secure along the end-grain sides only). I'm just wondering if this approach might be better for keeping the panel centered in the frame, while still allowing it to move freely. I drew up a sketch of what I have in mind; basically the panel would be nested in foam on all sides, so that it would be held in place, but also be free to expand and contract across the grain, and the foam behind it would, ideally, be thick enough to allow the panel to warp, if necessary. 

    Regarding the front of the rabbet, where it contacts the painting: I've always used acrylic felt tape as padding, there. Is that a bad idea for works on copper? I had thought that acrylic felt was generally safe to use with anything. 

    2019-01-19 16:55:36
  • EditDeleteModerator Answer

    I understand that modern quarter sawn is generally the best available, but if it can be obtained, rift sawn (what we call radial cut) makes the most dimensionally stable wooden panel.  What you illustrate is probably fine for the size of the panel you are using, however, as both Hugh and I indicated, natural wooden panels are best held into the frame solely in the center at the top and bottom. You method would be fine if you used a very soft foam which would allow a good deal of movement in the panel. Finally, acrylic felt is fine. I was actually referring to felted wool, as I know many people associate the word “felt” with that historical product.

    Brian Baade
    2019-01-19 18:20:00
  • ApproveRejectUn-ApproveUser Comment

    ​Thanks, Brian and Hugh!

    I've looked for rift-sawn lumber, but it's pretty hard to find, even at my local specialty lumber shop that caters to furniture makers. They do get a variety of quarter-sawn woods, though, so I usually sort through that stock and look for boards where the end grain runs as close to perpendicular to the faces of the board as possible. 

    2019-01-19 18:37:32

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