Canvas is a great surface on which to paint, but can be subject to dents and bumps when moving and storing, and can stretch and sag when exposed to changing temperature and humidity over time. If not stored properly, with the frame or stretchers securely resting against another frame or flat hard surface, a corner from one painting can poke into the canvas of another, leaving an unfortunate dent. All is not lost, though. There are several things you can do to rectify the situation and smooth out the dent. Following are some tips from readers as well as others.
Removing a Dent or Bump in a Canvas
If you lightly moisten the back of the canvas where the dent is, it should dry smooth. Tip from: Arthur.
If you're trying to remove a small dent in a canvas and the trick of spraying the back with a plant misting bottle full of water doesn't work, try using a professional spray starch in a can. But, like with water, don't oversaturate the canvas. Tip from: jlp1016
Spray the back of the canvas using a plant mister or other spray bottle and rub the water into the canvas with a rag. You don't want to use too much water but enough so that the water works its way into the weave of the canvas. Then press a flat object against the dent for a minute and let the canvas dry. The canvas will become taut and the wrinkle or bump will smooth out.
Another option is to lay the painting face down on a clean thick cotton towel. Then, using a steam iron held above the back of the canvas an inch or so, lightly release steam onto the dent or wrinkle until it is wet (no more than a minute). Wipe off the excess water and then let the canvas dry upright.
You can also use a blow dryer to hasten the drying process and to promote tightening of the canvas.
If the dent or wrinkle is in the corner between the canvas and the stretcher bars you can dampen a piece of paper towel or a sponge and slide it in the space to wet the canvas from the back, and then remove it in order for the canvas to dry and tighten.
Tightening an already stretched canvas is easy: I use a mister or a spray bottle with plain water (cold or hot). Spray the back of the canvas, then using your hand or a damp sponge spread the mist around and right up to and under the stretcher bars. Don't over-wet the canvas -- it's not necessary to wet it to the point of dripping, after all. Cotton duct canvas is made from 100% cotton and you know how cotton shrinks, right? Repeat, if necessary, after it dries, which is almost immediately. Tip from: Linda Folks
The Masterpiece Artist Canvas Tight-n-Up Canvas Retensioner Spray mentioned above can also be used to tighten a loose canvas. Spray the solution over the whole back of the canvas and the surface tighten as it dries.
You can also use canvas keys that come with some pre-made stretchers to correct loose and sagging canvases.