Or place your teacup on an ice bed.
Would take long for the liquid to cool through the glass...
Why on earth do you drink your tea out of a glass? Use a teacup or mug like a normal person.
I meant the material is glass. Teacups are made of glass, at least mine are...
ehhh, i thought teacups were made of ceramic or porcelain to be precise, rarely see heat-tolerant glass being used for teacups or coffee cups.
It doesn't really matter, does it? Heat capacity of glass/porcelain is negligible to the capacity of water (it is 4 times lower), but it really depends on type of glass e.g. fiberglass is a good heat conductor. TLDR: You want copper teacup.
some glass tends to crack at elevated temperatures, you don't see wine glass being used as teacups right?
Never had that problem with the glass I use.

thats because thats made of Borosilicate glass. a lot of other glass types cant tolerate sharp temperature gradients, which triggers thermal shock, causing cracks to form.
though tempered glass should be a bit more tolerant of sharp temperature gradients, but not all are.
Copper is a precious material to make a glass with.
i dunno about copper being used as a glass, but i've seen aluminum being used as bulletproof windshields.