Pretty slick stealth gloat............... What our son and i have always done, is scrape them with a pocket knife. It is something i always liked to do when watching TV, or some such. I imagine there is some kinda scientific way to go about it, but we never looked for a better way. We just work on them every now and again, until they are mostly clean. If you don't mind, could you take a photo of them? Some ivories are so very pretty.