Bitossi is stamped and was imitated. Anyway, this is a direction to look. On ebaydot com Pottery and Glass board, member wdel gave expert advice on Bitossi and Italian 20th century ceramics but the boards have changed and I don't go there anymore.
Bitossi call this colour "Rimini Blu". Bitossi spelled with double t is a popular misspelling but useful for Search. I am sitting on the fence over whether this is Bitossi. I think the glaze is less smooth than real Bitossi. I've only had a couple of pieces, most memorably a red owl figurine which had a beautiful dense but vibrant glaze.
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