Ask the Expert: "I delivered some paintings to a gallery several weeks ago. They were on oil-primed linen which I stretched myself over heavy-duty frames. They were tight as a drum when I dropped them off, but now the gallery has informed me that they have sagged too badly to be displayed. What might have caused this? Is there anything I can do to fix it? I've heard of a tightening spray, and also I know some artists spray water to tighten canvas."
This happens occasionally to every artist, and it's especially troublesome when the picture has already been delivered.
Linen fibers are at their longest when dry; for this reason, linen canvas can go slack if stretched in a humid environment. Manufacturers recommend if at all possible to stretch linen canvas on a dry day. It might be possible you did your stretching when it was humid, and they subsequently became loose.
Tightening spray is not for use on oil-primed canvas; it's best reserved for reversing isolated dimples in acrylic-primed fabric. We don't recommend water for this application since it could soften or swell sizing and affect the oil priming layer.
If your stretchers already have keys in place (small wooden wedges), you could instruct a curator or framer to drive them in a bit more to re-tension the pictures. (This can be tricky if the frame is tight fitting, but a good custom framer should know to accommodate eventual keying out.) If the canvas was delivered without keys, you could have them order the type that matches your stretcher and insert them as shown. If this doesn't work, re-stretching might be necessary.
To remove staples, place the canvas face-down on a hard surface covered with clean cloth. Use a nail puller to carefully lift staples and use needle-nose pliers to pull each. Be especially careful not to gouge fabric. Keep stretchers aligned with the picture and re-stretch. Insert keys until full tension has been achieved.
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