I think I would take some scraps, write on them with a sharpie, let it dry, pour water on it and see what happens, if nothing happens, I think I would put the sharpie scraps into a bag and wash them as you would wash a quilt and dry....see what happens. I know sharpie marker does not stay on some surfaces. I mark my insulin pens with them, it stays on one but not the other. Also I use masking/painter's tap to mark dates on the food I freeze. Sometimes it comes off.