Bone china is also transluscent, but isn't glass.
Real Vitro-Porcelain should be opaque, and will probably show mould seams somewhere (I think)
The name Vitro-Porcelain is misleading, perhaps, to folk who might have little experience of C19 pressed glass. It isn't porcelain but glass (the give away is in the Vitro bit), and being opaque and frequently coloured does have the appearance of china/porcelain.
Sowerby are credited with the invention of 'Vitro-Porcelain', and its success was due possibly to the fact that whilst cheap to produce, it imitated the more expensive genuine porcelain that the working classes couldn't afford.
I've never tried making weight comparisons between real china and Vitro-Porcelain, but would imagine the glass form to be heavier than the china equivalent.
No problem in quoting or linking to old posts by the way.