Did I mention the artifacts have pictures of a burning dwarf ? I have four dwarves down, one fire imp caged, two killed, one roaming free on the surface, and a single magma man still at the bottom of the magma pipe. The fortress is still young, so no military yet. I think will give a shot at markdwarves
--
Aykavil
Making lots of Obsidian is quite easy if you know how to pump water to the level of the magma vent. Channel out an area for the obsidian "factory" (I prefer to drop just below the surface and dig (not build) a series of up ramps. You don't have to worry about cave ins or getting stuck like channeling and as long as your ramps are only one z level underground, the dwarfs will clear out an entire area pretty quick.) Prepare to pump water into this area by placing your last pump on ground level.
Create a channel leading from this new formed open area to the magma and let it fill up (even partially) with magma. Pump water over top of this magma making sure not to cap the magma pipe to turn it into obsidian, channel out the factory originally and clear out the obsidian. Rinse. Repeat.
Side View:
_ = channel
X = rock
M = magma
~ = water
P> = pump from water to pit
above P>
water ~~~XX______XXMMMMM
I normally place my crossbowmen on a wall surrounding this area if there are creatures in the lava. The wall lets them get a good shot and it also helps control the water for efficiency. Just don't put a wall where you need to dig out the magma channel. (You can also build a floodgate out of magma safe material, but it's not the easiest stuff to come by. Check the wiki.)