Insulators with "stuff" inside. Opalescent, bubbles, garbage, and milk.
The light source was a Turtlelite II white LED flashlight, shining up directly under the insulators.

Left: Very nice medium opalescent CD128 Hemingray E-14B.
Right: CD170 with bubbles and lots of snowflakes - does not show up on photos. :(

Left: Am. Insul. Co. CD145 base-embossed in bubbly "Windex blue" with milky swirls
Right: Am. Insul. Co. CD145 base-embossed with milk, garbage and amber crap in the glass.

Left: Milky, bubbly CD135 shoulder-embossed Chicago diamond
Right: CD123 EC&M, exceptionally bubbly and with some steam.

All three: Purple CD161 Californias with bubbles.