It will happen to most of us at some time, and sometimes it will happen to our clients....You've stored a canvas or painting and no matter how carefully you did that, a dent appears in the canvas. Luckily, it is quite easy to fix!
Turn the painting over, and if there is a paper backing on a framed canvas, remove the paper backing.
Take a mist spray bottle and fill it with warm water. Spray the back of the canvas (never spray the painted side) lightly with water and use your fingers or a sponge to lightly massage the water into the canvas. You do NOT want to spray too much water that it completely saturates the canvas and goes through to the painted side.
Place the canvas somewhere warm to dry, but not in direct sunlight or near a heat source as it may dry too quickly and cause further damage.
The process of the water drying will tighten the fibres of the canvas and the dent will disappear. If the dent is particularly stubborn, you may need to repeat the process more than once.