While perusing the wiki to solve the mystery of a drowned fish, I came across this bit:
"Casting a cage in obsidian will not harm the occupants (though the temperature might if the cage is subjected to magma for very long)."
This led me to the question: What about freezing a cage? One winter embark later, here are my results:
I used a meeting zone, a pillar and a floor to cause a minor cave-in, resulting in two trapped dwarves. One, a visiting Mason diplomat, went berserk at the outrage of being attacked. The other, a friendly Engraver, was more cooperative and remained a citizen of the fort - listed as "No Job (Caged)" in the citizen screen.
An aquifer, floodgate and surface-exposed room were used for controlled freezing. Constructing the cages in the appropriate tiles first and then freezing them had an odd result, allowing me to view the cages and see the dwarves' flashing faces despite them existing on top of/inside of an ice wall. Deconstruction of the cages was possible through the ice wall, resulting in the item teleporting to the nearest pathable adjacent tile.
A second method of dumping the cages onto the floor had a better result: solid ice walls with no indication of an item or unit inside, except for their status on my unit screen. With my test subjects incarcerated, I marked the time and began to wait.
While the Engraver died around when a dwarf might have died of thirst, the berserk visiting Mason did not. Not all !!science!! ends in drastic revelations, sadly, but it was nice to conduct an experiment. That said, there are some potential applications here:
-Creatures that can break out of cages might be safely contained within an ice wall.
-Necromancers, Vampires, Werebeasts and Undead could similarly be contained if necessary.
-Gremlins and other mischievous creatures may not be able to access an ice-encased cage.
-Had I a mechanism to run magma under the floors, it would be possible to unfreeze these poor souls on demand, even in adventure mode. I do not know if adventurers can interact with cages, however, and would appreciate any !!science!! information there.
Sadly, my dream of preserving dwarven children as popsicles until they reached maturity was thwarted. But such is the toil of dwarven !!science!!...