I have several pieces of pottery in an antique mall. Today, I found several pieces of my pottery had a white deposit on top of the glaze and even what appears to be under the glaze. I believe it is salt effloresence. These pieces have been at the antique mall for approximately 4 months...but the white deposit appeared just recently. It appeared to be under the glaze on one piece and is now pitting. Has anyone experienced? Any suggestions on how to avoid it?