My mention of a "commercial" chalcedony was my repeating of something Adam Aaronson posted not too long ago.
I assume, possibly wrongly, that the non-bought-in-block stuff was created by the glassmaker from different colours of glass as well as (sometimes) the inclusion of silver salts.
I got the impression that the commercial bought in block stuff just "created" the chalcedony effect as it was worked.
Maybe we need Adam to clarify?