Tom writes:">Dan Mouer mentioned sherds 1 cm in diameter.  That seems
awfully large to be
>a gizzard stone.  How large are gizzard stones anyway?"
 
My statement was misleading. Actually the sherd is a thin square of
fine underglaze blue Chinese export, about 1760s, roughly 1 cm.
square and perhaps 10mm thick. I wouldn't want anyone to accuse me of
postmodern imprecision.
Dan