From the renovator - The hatching egg was in quite good condition good metal, so the black came off with 20 minutes hot alkali soak, and the pitting from the removed black worked down using just a tiny 3 inch by 4inch piece of 1000 grit wet and dry. i.e. did NOT have to grind away much metal, then finished with renaissance wax. Mind you it is not as simple as that in that the how much and how of this and that to do something that works is result of lots of experience. Resulted in something in much better condition and originality than the one in the textbook which had been rather heavily worn down.