nudie drinking glass- how??

[tigers]

dear folks,
you know those drinking glasses with pinup girls or guys on them whose clothing disappears when the glass is filled with a cold drink?
how do those work?
and you know those similar glasses with a clothed hottie on the outside and the same hottie bared on the inside? how is that done? silkscreen twice? decals? how is it waterproof?
DANDY products in chicago used to make the disappearing-clothes kind, but i can't find any info on them.
thanks!!!

tigermanx

[hawksgirl]

Disappearing clothes: maybe temperature-activated inks, like they use on those make-up Barbie dolls and such. Thats my best guess.

[Squink]

-No answer here, just a couple links, and some speculation:

Nudie glasses like these, made by Libbey.
The pictures are decals, and were produced at least as far back as the 1940's, so the tech isn't going to be very high.

The disappearing parts are white and, if I recall correctly, somewhat rough. I wonder if condensation on the decal caused the frosted bits to go transparent. There'd be no need for special inks to do it that way, but I don't have a glass handy to check.