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[HatfieldCW]

Quick question:  How deep does magma have to be before it'll turn into a tile of obsidian when doused with water?  My obsidian farm is poorly designed, and it takes ages to fill up.  Can I dump the water at 4/7 and get the rocks?

[yuhhaur]

http://www.dwarffortresswiki.net/index.php/Magma
Read through "Producing Obsidian" Section. recommended depth should be 2/7 for magma. IMHO it also depends on whether you pour the magma to water or water to magma. I would suggest that you pour 3/7 of water to 2/7 of magma. This can ensure that there will at least be enough water to fuse the magma into obsidian.

[Albedo]

I believe 1/7 of magma is sufficient - but it evaporates, meaning that if it does, then you lose any obsidian that would be manufactured on that tile, and the water that falls there is just... wet.

Sorry, but your recommendation of 3/7 water is absurd, and shows a lack of actual experience - 1/7 is all you need, but somewhere between that and 2/7 is recommended to avoid the risk of "not enough", and leaving raw magma - which is worse than no obsidian, since you can't safely access the 8 tiles around it.

[decius]

You need 2 of one, to which you add one of the other. If adding water from the top, you need enough water to cover the entire field to 2/7. One per tile will turn to obsidian, leaving 1 on top which allows the rest to flow across.

[HatfieldCW]

Thanks.

[yuhhaur]

let me check and do some calculation.

Code: [Select]

|___X...|    z+1 (water pool) 
    |...X___|z (lava pool)
    |___|    z-1 (obsidian)

X = floodgate
. = open space
_ = pool/reservoir
| = wall

I have a lava pool size of 7x7 (x6 or x7 depth, depends on the flow of the magma) = 294 to 343 magma. Upon release the floodgate it is then flow (at least) 7x7x6 = 294 magma to a 13x13 = 169 obsidian farm. So the depth would be 1/7 or 2/7.
My water reservoir is sized at 7x9x7 = 441 and it is situated 1 z-level above the lava pool. upon open the floodgate at least 7x9x6 = 378 are flowing out to the obsidian farm. So I have 378/169 = 2.2 water per lava for the production of obsidian. Excess water is evaporate fast enough upon my miner's channeling activity.
I am taking into consideration of not 100% of lava/water from the pool/reservoir would flow into the farm.
So what is wrong with 3/7 of water? This would guarantee 100% forming of obsidian.
I can harvest at least 60 obsidian per cycle.

[decius]

let me check and do some calculation.

Code: [Select]

|___X...|    z+1 (water pool) 
    |...X___|z (lava pool)
    |___|    z-1 (obsidian)

X = floodgate
. = open space
_ = pool/reservoir
| = wall

I have a lava pool size of 7x7 (x6 or x7 depth, depends on the flow of the magma) = 294 to 343 magma. Upon release the floodgate it is then flow (at least) 7x7x6 = 294 magma to a 13x13 = 169 obsidian farm. So the depth would be 1/7 or 2/7.
My water reservoir is sized at 7x9x7 = 441 and it is situated 1 z-level above the lava pool. upon open the floodgate at least 7x9x6 = 378 are flowing out to the obsidian farm. So I have 378/169 = 2.2 water per lava for the production of obsidian. Excess water is evaporate fast enough upon my miner's channeling activity.
I am taking into consideration of not 100% of lava/water from the pool/reservoir would flow into the farm.
So what is wrong with 3/7 of water? This would guarantee 100% forming of obsidian.
I can harvest at least 60 obsidian per cycle.

Math check:7x7 magma pool, x6 or x7 deep, can put 7*7*5=245 to 7*7*6=294 magma into the pit. (the last 1 will never flow out, only evaporate).

Assuming no evaporation, that should give you from 76 to 125 tiles of 2/7 magma. But that's not the whole story: When magma flows into a tile containing 1 water, you get steam and 1 magma in the tile. When water flows into a tile containing 1 magma, you get steam and 1 water in the tile. The two can and will go back and forth a little bit before one or the other runs out. That wastes magma.

I suggest you expand the lava pool to 7x9. It should take only a little longer to fill, but should get you the max of 169 obsidian/cycle, and have a little buffer for magma evaporating as it flows.

[Albedo]

So what is wrong with 3/7 of water? This would guarantee 100% forming of obsidian.

Once.  Only the first time. 

As pointed out above, you want the "factory floor" dry before you start the next batch - this can take quite a while if you over-water.  And if you start pushing it then you're either losing production or getting further out of balance.

It'll work, just not as well as it might.

(Are you using floodgates or retractable bridges? The latter are recommended for their even distribution.  A bridge can only be 10x10 at max, so you'd either need more than 1 or just center it and call it good.) (Rather than 13x13, 10x17 would have been better for that purpose - meh.)

[yuhhaur]

I suggest you expand the lava pool to 7x9. It should take only a little longer to fill, but should get you the max of 169 obsidian/cycle, and have a little buffer for magma evaporating as it flows.

Thank you for the suggestion. I rather waste water than magma. That is why I dug my water reservoir to be 7x9 instead of 7x7.

So what is wrong with 3/7 of water? This would guarantee 100% forming of obsidian.

Once.  Only the first time. 

As pointed out above, you want the "factory floor" dry before you start the next batch - this can take quite a while if you over-water.  And if you start pushing it then you're either losing production or getting further out of balance.

It'll work, just not as well as it might.

(Are you using floodgates or retractable bridges? The latter are recommended for their even distribution.  A bridge can only be 10x10 at max, so you'd either need more than 1 or just center it and call it good.) (Rather than 13x13, 10x17 would have been better for that purpose - meh.)

Yea, but my lava/water reservoir are designed that it feeds 2 farm instead of 1. I will have the first farm drying while I work on the 2nd farm. Plus the digging time... more than enough time for the water to evaporates.

And, I use floodgates. 1 reservoir has 2 outputs to 2 farm. My obsidian are piling up before I can used them up.