A famous essay by Beatrice Warde used the metaphor of the ideal wine glass to illustrate the function of typography. She argued that typography should be, effectively, invisible, serving to unobtrusively facilitate the communication of the writer's thoughts to the reader as effectively as possible.
While this is a function of typography, and likely the most common function of typography, it may perhaps be argued with validity that this is not the only function of typography.
The specific example she used corresponding to the kind of typography she advocated was, of course, a "crystal goblet".
It occurred to me, recently, to ask, is there such a thing. Did she mean a wine glass made from quartz ("rock crystal"), or one made from what is usually called "crystal" in the area of glassware: glass with 17% or 24% PbO content - what would be called "flint glass" in making lenses? Apparently, it was the latter; as opposed to storing wine for long periods of time in a crystal decanter, drinking wine from a lead crystal goblet isn't considered too hazardous, except perhaps by the government of California.
But that raises another question. I suppose that a crystal goblet doesn't release lead to nearly the extent as a solid lead, or even pewter, mug, but given that the ancient Romans used lead cups to drink from precisely because they imparted a sweet flavor to beverages (by causing them to be contaminated with lead acetate)... well, not only is her position apparently controversial, but it seems her metaphor is deeply flawed.