MURANO GLASS- Unusual OYSTER SHELL Color & Look

We've collected and sold hundreds of Murano Glass ashtrays over the years and some were quite unusual and colorful, but this one is special. The black outside layer is actually an opalescent deep purple and the inside rings and striations are a clammy grey/red and white. You can actually see right through the layers of color. The under-base is recessed and polished, the shape is of a clover leaf and it measures approximately 6"across and 3" tall. When I look into it, it reminds me of a recently shucked oyster or clam shell. Anyone know which of the Murano Factories specifically made this Ashtray? I suspect AVEM but it's a guess. RER(BOB)