Editing v0.34:Obsidian farming

{{Quality|Exceptional|20:58, 29 April 2013 (UTC)}}
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Obsidian farming is a method of producing [[obsidian]] efficiently. When [[magma]] contacts [[water]], a tile of unworked obsidian spawns on the meeting point and both fluids disappear from that tile. Obsidian is a moderately-valuable [[stone]] and both magma and water are renewable, resulting in a theoretically infinite supply of mid-value stone goods.

== Floodgate method ==

A typical method of farming is as follows:
* A rectangle hall, 2 z-levels high is dug out/constructed
* Lower level of the hall is fed magma from a [[pump]] (otherwise it will fill very slowly)
* Upper level of the hall is covered in water ([[pump]] is a good idea too)
* Water gets removed (by a [[pump]], opened floodgate etc.)
* Resulting obsidian (on the lower level) is designated for ramping or channeling (floor between levels needs to be removed for the farm to be reused)

For more advanced farms, one can have multiple layers of magma and water - each new layer adds another layer of obsidian, so this method is far more efficient (N - number of fluid layers, (N-1) - number of obsidian layers). Your dwarven ingenuity should be shouting "OBSIDIAN FORTRESS" by now, by the way.

== Bridge method ==

{{diagram|spaces=yes|color=#888|\
      z              z-1           z-2
 ╔══════════╗   ╔══════════╗   ╔══════════╗ 
 ║[#B0B]╔[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]╗[#BB0]┼   ║..........[#BB0]┼   ║++++++++++[#BB0]┼ 
 ║[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║  .[#0BB]╬..........║   ║++++++++++║ 
 ╝[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║   ║..........[#0BB]╬.  ║++++++++++║ 
[#44F]W[#FFF]╥[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║   ║..........║   ║++++++++++╚ 
[#44F]W[#FFF]║[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║   ║..........║   ║++++++++++[#0F0]X[#F00]M
[#44F]W[#FFF]╨[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║   ║..........║   ║++++++++++╔ 
 ╗[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║   ║..........[#0BB]╬.  ║++++++++++║ 
 ║[#B0B]║[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]+[#B0B]║║  .[#0BB]╬..........║   ║++++++++++║ 
 ║[#B0B]╚[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]═[#B0B]╝║   ║..........║   ║++++++++++║ 
 ╚══════════╝   ╚══════════╝   ╚══════════╝ 

}}

Another, possibly simpler, design is 3 z-levels high:
* Uppermost level contains a water reservoir, the floor is channeled out and covered with a retracting bridge (shown in purple), to drop water '''when needed''', and, optionally, a raising bridge (in white) to control water flow; the combination of retracting and raising bridges will result in a measuring reservoir, which drops no more water than necessary. It may also include a door for maintenance purposes.
* Middle level is an access room; floor may be channeled out or ramped out from below, but it should not be there. It should include an access door, and optional drains to remove excess water (shown in cyan); the spare water may be pumped back to the reservoir, dumped in the caverns or an aquifer, or left in a large room to evaporate. Outside the farm must be two levers; one controls the bridges in the water reservoir, one which controls the magma floodgate.
* Lower level is the magma reservoir; the floor should be intact. The magma supply should be controlled by a [[magma-safe]] floodgate (shown in green). Again, this level may include a magma-safe door for maintenance access.

Requirements: 
* 6 mechanisms (8 if measuring reservoir is used), one of which must be magma-safe.
* 1 magma-safe floodgate
* 1 bridge (2 if measuring reservoir is used)
* 3 z-levels you're willing to dedicate to an obsidian farm, with easy access to water and magma.

Operating instructions:
# Open the floodgate and flood the lower level with magma.
# Close the floodgate.
# Retract bridge and drop the water onto the magma.
# Unretract the bridge.
# If necessary, wait until any excess water has drained away - if you built a measuring reservoir, there should be no water left on top.
# Mine the obsidian using channels/ramps.
# Haul the obsidian stones to a stockpile.
# Repeat.

As a bonus, the obsidian casting process can also serve as a convenient garbage disposal.

== Notes ==

*'''Make sure that the Temperature setting is enabled in the [[d_init.txt]] file for obsidian farming to be feasible'''; otherwise, the tiles will not cool down after the obsidian is formed, and dwarves will refuse to get close, thinking it incandescent despite no magma being present.
*Keep in mind all usual precautions for handling big amounts of both [[water]] and [[magma]].
*Unlike water, magma normally flows very slowly and pressure doesn't affect magma at all. Because of this, it's always preferable to pump magma rather than letting it flow, even when the obsidian farming chamber is on the same z-level as magma, or it might take much longer than you'd expect. Pumped magma however ''will'' be pushed up by pressure, up to the z-level of the pump.
*When pouring water over magma without dispensing the exact amount, you'll probably end up with excess water on top of the obsidian. Make sure your design includes a way to easily dispose of this water.
*For the same reason it's usually better to drop water onto magma and not the other way around - excess water is much more manageable than excess magma.
*Remember to turn off any inflow before digging out obsidian, or the moment the obsidian holding it off gets dug out it will resume flowing, likely leading to [[Fire]] and [[Fun]].
*Note that if you add water to a tile which is as little as 1/7th full of magma, you'll create a full block of obsidian. This is particularly useful when you're operating a repeatable [[magma piston]] since one block of obsidian will displace 7/7 units of magma, and you'll only need 1-2 units of magma to make a block of obsidian to get 7 units of magma.