Rubbing alcohol to tighten a canvas
Hi all, I have a question about oil paintings that I cannot find the answer to anywhere. I hope someone can help me!
I had been told that you can spray rubbing alcohol on the back of a stretched painting if the canvas becomes loose in order to tighten it again. I've done it before with no problems. But recently I did it on an oil painting and something weird happened: around some small cracks in the painting (it's pretty old) there appeared some cloudy white residue (?). I have no idea what it is- when I gently rub it with water, it disappears, but reappears once dry. I suspect the canvas was not primed, but I'm not sure.
I'm not so much interested in the cause (though it would be helpful for future reference) but more in how I can fix it. I'm able to touch it up but since that's such a pain in the butt, I wondered if anyone has experience with this kind of problem and if there is some other way to fix it. Any ideas would be greatly appreciated!
Thank you so much in advance! :]