Now why didn't I think to call Case??? That was easy! I called the
  800 number that comes up if I search on Case Cutlery and it turns out
  to be a vendor of Case products (Shepherd Hills Cutlery). They gave
  me the number of the Case factory and I talked with "Jim". He
  immediately pulled out a 1985 catalog and read the description to me.
  It's "an alumina ceramic stone, harder than natural stone and with a
  more uniform textue". He said they get quite a few queries for them,
  but they're no longer made. I guess I'll keep it. Charlie Rodgers
  Clinton, Maryland

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