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 farming techniques, obsidian may be cast into above-ground structures or used to fill unwanted rooms, allowing engravable walls in areas otherwise not possible.

basic approach

There are 3 levels to the standard obsidian "farm"; the lowest for magma/obsidian, the middle for dwarves to dig down and channel the obsidian out once it's been created, and the upper-most for a water reservoir. This is basically all one open area - no floors exist between the levels.

Level +2   ~~~~    <- water reservoir
Level +1           <- work area & access for miners for channeling 
Level 0   xxxxxx   <- magma/obsidian 

 SIDE VIEW

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.

(* The math works like this: Determine the size of the magma level, the number of tiles you want to cover in water between 1/7 and 2/7 when the bridge drops the water. (Better a few too many than a few too few!) Multiply that by 1.5 (average of 1/7 and 2/7). Divide that by 7, and round up to the nearest whole number. This gives the number of 7/7 tiles for your water reservoir.

Some players have a "measuring" reservoir that then dumps water onto the bridge reservoir for even distribution - see below. Others use hatches or multiple smaller bridges to spread the water out across a wider area. As mentioned above, there are many, many different tweaks and "improvements" to this design.)

One Z-level below the reservoir and above the magma a "working area" should remain empty for your future obsidian miners, covering the full area beneath the bridges plus a single row 'ledge' on at least one side (left/west is best). Access to the digging level is only required from this on this mid-level, and lockable or linked doors are strongly suggested.

The area beneath this access area, the lowest, should be channeled out - this is where the magma will be poured, prior to water being added. The easiest/safest ways to do this are one row at a time, from east to west, or by digging ramps and then removing them all. The ledge allows the last row of the whole area to be easily channeled. In-flow of magma into this area is best if kept simple - just put in some gates and dig out a path. If obsidian is created in the middle work level (rather than in the lowest magma level), the water-reservoir bridges will be destroyed when that middle level is channeled out, requiring a re-building process.

The process then is:

• Clear all dwarves from area, lock/seal all access doors. (Not actually necessary, but strongly recommended! (Unless you want to cause a few "unfortunate accidents". Watching magma touch water is truly a sight for the nobs.))
• Fill lowest level (only!) with magma, at least 2/7.
• (Close magma gate(s) if you have them.)
• Drop water from reservoir. (Inflow to reservoir should be sealed to prevent excess flooding.)
• Once water has turned all magma to obsidian, open access to middle area for workers.
• Channel out obsidian, begin hauling (if no bauxite gates are used (see below), do NOT channel "plug" yet!)
• Refill upper water reservoir while harvesting operations are ongoing
• repeat

Note that a ramp can be dug for the haulers, or doors built on the lowest level. These do not need to be magma-safe (as they are not "submerged" in magma), but the obsidian in front of them must be channeled free for them to open. It is (again) strongly recommended that these are locked or link and shut while the magma is flowing.

no bauxite

For a no-bauxite-necessary method of producing obsidian, it's necessary to use water to "plug" the open channel that allows the magma to flow into the lowest level. Once the obsidian is mined and recovered, that "plug" is channeled out last, and the magma flows as above. (Make sure the dwarf who channels out that plug has a safe escape route!) See here.

Dangers

Dangers are many, and experience is a hard teacher. Fun is only funny up to a point. Some of the common dangers/warnings include...

• Be careful pressurizing the lava via pumps, as this can cause the lower reservoir to overflow.
• Be aware of up-staircases or other floor-perforations below the magma level that may cause leaking/flooding.
• Label your levers! (see below)
• 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 disrupt work and evaporation may take too long and water can build up over repeated cycles.

Tricks & tips

self-measuring reservoirs

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/retract (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. The simplest method is to use retracting bridge(s) in the chamber, to drop the water, and a raising bridge in the inflow, to control the water.

As tempting as it is to simply use a door to close the incoming water, it won't work. Levers work on a system which means, in this case, open doors/hatches and retracted bridges happen on the same signal. The only way to do it is to use a raising bridge in the inflow, or a door/hatch on a separate lever.

double-wide magma channels

To designate a large area for channeling, one row must be designated at a time to prevent idiot miners from trapping themselves on an isolated island of stone. While this may be the best use of space, creating double-wide channels for the magma/obsidian (possibly with double-wide bridges/water reservoirs immediately above them) is far easier to designate when it comes time to harvest the obsidian, and no dwarf will ever channel themselves into a corner.

            ......................
            .cccccccccccccccccccc.
            .cccccccccccccccccccc.
            .cc...................
Magma       .cccccccccccccccccccc.
Source -> Gcccccccccccccccccccccc.
            .cc...................
            .cccccccccccccccccccc.
            .cccccccccccccccccccc.
            ......................

 G = Magma-Gate (lowest level)
c = channel (lowest level)
. = floor (mid-level)

labeling levers

One way or another, whenever handling magma it's a good idea to be sure which lever is which. Using the 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 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.

---

Using Pressure

It is very useful to note that magma that is pumped will carry pressure and move up z-levels. It is possible to use this to set up a very simple and foolproof magma farm.

First one level below where you want your farm you set up an access point for magma. Then on the level of your farm you build a pump. Connect the pump with your farm with a pipe on the level below.

(Side View)
        Pump
           |       Farm
           |       |
           V       V
        ######
        # => #_____ _____#
Magma-> ~~##        ######  
Source  ##################

When ready to fill just start pumping.

(Side View)
        Pump(Running)
           |       Farm
           |       |(Full of Magma)
           V       V
        ######
        # =>~#~~~~~~~~~~~#
Magma-> ~~##~~~~~~~~######  
Source  ##################

Once it gets above 2 units on each tile stop pumping and pour water on the farm.

(Side View)
        Pump(Stopped)
           |       Farm
           |       |(Full of Obsidian)
           V       V
        ######~~~~~~~~~~~~ <-- Water
        # =>~#############
Magma-> ~~##~~~~~~~~######  
Source  ##################

Then drain the water and dig up stairs in the obsidian. No need to channel the upstairs will allow your Dwarves easy access from above, and so long as the pump is stopped no magma will flow into the farm.

See also: Obsidian Farming 101, for an excellent forum discussion of this topic.