Ever the efficient baron, I have (re)discovered that nickel cages with goblins in them do not melt in magma, and yet the goblins burn to death regardless. This means no more forging of execution cages to be dropped into magma, instead I simply place the cage (or even put it in a stockpile in the room, building is unnecessary), flood in magma, and wait for the goblins to burn to death.
However, I also noticed something very strange while, ehhmm, tossing out my large wood, copper, silver, and gold cage stores. Specifically, I have noticed that some of these cages melt, releasing their inhabitants, long before the inhabitants themselves become completely disabled. Specifically I have had several incidents of fatless goblins running amok in my magmacution chambers. I theorize that the lower the melting point and specific heat of the material of the cage, the faster the cage will melt, and the least amount of harm will come to the prisoners inside. With renewed talk of dwarven drop pods, I must propose the following idea:
Create a pit, with a ramp and 1/7 magma in it. Place a dwarf with fixed heat armor, or armor that does not transfer heat very quickly(netherwood would work, not sure how to fully outfit him, Whats the best material bay1?) into a cage (Easiest to do if you have criminals -- put dwarf in military, give him gear, temporarily assign a sheriff, build a meltable cage and he will appear in it), finally, drop the cage containing the dwarf from an arbitrary height above the pit. He will take no damage from the fall, and when he hits the ground, the cage should melt, releasing him with only minor burns.
The only use I have thought for this so far is what is perhaps the most epic entrance to an arena I have ever thought of, but uses are irrelevant. The question is, what are the best materials for this, and is modding going to be necessary to make this feasible?