anaclastic glass

Wiktionary

1. n. A glass or phial, shaped like an inverted funnel, with a very thin convex bottom that can be made concave or convex by sucking out or blowing in air.

GNU Webster's 1913

1. adj. a glass or phial, shaped like an inverted funnel, and with a very thin convex bottom. By sucking out a little air, the bottom springs into a concave form with a smart crack; and by breathing or blowing gently into the orifice, the bottom, with a like noise, springs into its former convex form.