Traveling around, I occasionally get dents or scratches in my canvases. On a small ding, usually just wetting the back slightly on the deformed spot is enough to stretch the linen back into place*. Recently however I had a long line appear on a commissioned painting which was almost finished (something probably leaned on it in my car). As the painting was done for the most part in the fall, I would have had to wait half a year to paint it again.
Instead I had a professional restorer, Daniella Murphy Corella, come by the studio and take the painting to be ironed. I ended up doing all the work myself under her guidance and I’ll share what I learned.
First off I used a regular household iron. The iron must be able to operate at lower temperatures, i.e. you can place your hand on it without burning yourself (do this carefully). If your iron doesn’t go to just ‘warm’ you can put newspaper between it and the canvas.
Second, you take out all the water from the iron and make sure it doesn’t steam the canvas.
Third, you unstretch the canvas and place it with the painting side down on silicon paper or something that the paint wont stick to.
Then you iron the canvas on the back where the problem area is for a very long time. I probably ironed for over an hour total, applying pressure the whole time. At the end the line was gone and the canvas wasn’t deformed in any way by the low heat. Apparently, if you use high heat (or water), the canvas will get waves in it which makes things much worse.
*One note about wetting the back of the canvas to get rid of dings. In my experience, if it doesn’t come out the first time you wet the canvas, don’t try it a second time or the ground can crack.