One of my small glass cups has been used for quite while for colloidal gold. I was at a loss when I tried to clean it such that the ruby red hue in it's wall disapears. I tried soap, dish washing liquid, and hydroperoxide to no avail. Finally I tried a few drops of Lugol's solution and it worked! The only drawback is my index finger got stained with iodine, which dispeared on its own sometime later.
