Brewer's: Venice Glass
The drinking glasses of the Middle Ages, made at Venice, were said to break into shivers if poison were put into them.
`Tis said that our Venetian crystal has Such pure antipathy to poison, as To burst, if aught of venom touches it.
Venice glass, from its excellency, became a synonym for perfection.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894