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
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
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
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
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.
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.
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