I have vintage lefton salt and pepper shakers in the shape of turkeys. The salt shaker very recently started to develope what looks like a lime coating. (There is not any salt in the shaker.) It is a white flakey substance that is coming from the inside, through the glaze. The salt holes are crusted over and the bottom is beginning to deteriorate. I have soaked it in vinegar, but as soon as it dried, the film returned. Does anybody know what this is and how to stop it?