Editing 40d:Obsidian farming

By mixing [[magma]] and [[water]], dwarves can produce [[obsidian]], a highly valued material. This process can be dangerous, but the dangers can be minimized if approached carefully.  It's advised that players research this before proceeding if they want to avoid too much [[fun]] all at once.

If you have a [[magma pipe]] (not a [[magma pool]]!) and an inexhaustible source of water, you can produce an infinite supply of obsidian by setting up an area for magma to flow (and later the obsidian to be dug/channeled out), and for water to be poured on top of it, creating the obsidian.  The trick is to use only as much magma and water as necessary, so deep water does not prevent dwarves from working in "[[dangerous terrain]]", and the magma pipe has time to refill between harvests.

There are as many designs for "farming" obsidian as there are players who do it.  Below is a basic plan; improvements are up to you and your imagination. For example, using sufficiently advanced pouring and framing techniques, obsidian may be cast into above-ground structures or used to fill unwanted rooms, allowing engravable walls and cave-in resistant areas where before there were none, respectively.

Magma is routed to flow directly into the lowest area, using doors/floodgates of [[magma-safe]] materials linked to a [[lever]] with a [[bauxite]] [[mechanism]] to turn the flow on/off.  Only a depth of 2/7 is needed (1/7 can work, but can also [[evaporate]] before the water is added, causing problems later - 2/7 to 3/7 is perhaps a good target to start with).   

The water reservoir is built 2 z-levels above this with a controlled inflow of water (more linked doors/floodgates), sized to provide just enough water to cover the magma area below at a depth of between 1/7* and 2/7*, to fully cover the magma but allow for [[evaporation]].  The floor of this reservoir is channeled out and replaced with one or more retractable bridges, linked to a (single) lever, to drop the water all at once.  It is not necessary that the amount/depths of water and magma be balanced, only the area.   

:* Clear all dwarves from area, lock/seal all access doors. (Not ''actually'' necessary, but ''strongly'' recommended!)

* Seal your dwarfs away from the magma until it is ''all'' obsidian.  Linked doors are the only "positive" locking system.  If you think you want to do it manually, keep the number of doors to a minimum.

* Try to balance the water - too little means left-over magma (which cannot be channeled around), and too much can [[dangerous terrain|disrupt work]] and evaporation may take too long and water can build up over repeated cycles.

To create a reservoir that measures a pre-determined amount of fluid, use a combination of door(s) (or hatches/floodgates) and drawbridge(s) attached to one lever, one at the inflow and one at the outflow.  When a lever is thrown one way, doors open and drawbridges "raise" (sealing any path they block); when the lever is thrown the other way, the reverse happens, the doors sealing and the drawbridges opening.  Clever use of this fact can allow liquid to fill a "measuring reservoir", which then seals the input while being emptied.  Once all the liquid is emptied, the lever is thrown again, the outflow seals, the inflow opens, and it refills to its full capacity, ready to deliver another pre-measured dose of liquid.

One way or another, whenever handling magma it's a good idea to be sure which lever is which.  Using the [[note|labeling]] function is a good idea, especially if you leave your fortress and come back later.  But a visual cue is also a good idea, either by making the levers of [[The Non-Dwarf's Guide to Rock|different color stone]], or adding colored flooring or walls around/near them.  Perhaps "red" for magma, "blue" for water, and "green" for the lockable doors - whatever works best for you.  And/or placing them in order of use, from left to right.  Anything and everything that makes it safer and more "fool proof" can only be a good thing.