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[Leonidas]

The wiki says that when magma and water meet, the water turns to steam and the magma turns to obsidian.  What it doesn't say is: How much?

Suppose that I drop a 4x4 square of 7/7 water into a large pool of magma.  How much obsidian will I get?  And if the magma has multiple z-levels, will the obsidian form at the top and then sink to the bottom?  If I trickle the water into the magma slowly enough, would that prevent the obsidian from forming?  Does each magma square effectively have a temperature rating that remembers how much water has fallen on it?

If I drop one 7/7 square of magma into a pool of water, how much water will the magma turn to steam before the magma solidifies into obsidian?  If I'm using magma to burrow through an aquifer on the same level, will the magma in front solidify and block the magma behind?  If I pour magma into the aquifer-pool from above, will the magma solidify immediately and possibly back up the system, or will it keep on oozing for a while so that the rest of the magma can keep pouring on in?

Sorry if these are hard questions, but I bet that others have already figured out the answers.

[eerr]

2/7+ magma hit with 1/7+ water will produce a full layer of obsidian.

If you start with a layer of water and add magma i'm not sure.

[Chromie]

If you designate a pond over obsidian, one bucketful will not generate obsidian, it will just eliminate one unit of magma. I haven't tested the limits of this though.

If you drop water into magma and it's not connected to anything you get a "a section of the cavern has collapsed!" message and it falls to the bottom. If it is connected to the side (say you're pumping water over the top of a magma pipe) it stays up, just like regular stone. If water flows diagonally, the obsidian formed will still fall, since it's not supported on its' orthogonal side.

If you drop the 4x4 square into magma, you'll get 4 blocks of magma, since it should obsidianify on impact, no chance for the water to spread out.

If I'm using magma to burrow through an aquifer on the same level, will the magma in front solidify and block the magma behind?

It will block. And even if you channel it out, it will keep obsidian-ifying in the same spot. You should drop water/magma onto the other from the top.

[Quietust]

If you designate a pond over obsidian, one bucketful will not generate obsidian, it will just eliminate one unit of magma. I haven't tested the limits of this though.

I've done this (to clear away HFS magma), and it doesn't just remove one unit - it empties out the entire tile.

[Shakma]

I did have a setup once that would occasionally leak 1/7 water and it would only make steam when hitting magma and not destroy any magma.

[XSI]

When making obsidian, try to add water to magma, not the other way around.

It's a lot easier to clear away excess water then it is to get rid of extra magma.

I also believe it's 2/7+ magma, and 2/7+ water, and never had any problems with it, except for when some noble decided not to pull the lever shutting off the water in his room.
(This can be read in 2 ways, and both are correct, I was using the same lever to flood his room and to add the water to the magma.)

[Quietust]

I once flooded my tower-cap farm to remove all of the dead shrubs and saplings (didn't work quite as planned, as it just resulted in tons of ashes), and when I re-irrigated it, a few tiles still had 1/7 magma on them, and when a tile of 2/7 water decided to spread out onto the 1/7 magma, it created a solid obsidian wall.

[Syzgyn]

I found recently that if you designate a pond directly above a layer of magma, the water will just remove individual units of magma.  If you go 2 z-levels or higher though, the same amount of water will turn it into obsidian.  However, if you designate a pond 1 z-level above solid ground and then let it spread out onto magma, that will form obsidian too.

[Derakon]

I've had the same experience as Syzgyn with respect to ponds, and with Quietust with respect to how much magma is needed to make obsidian. Don't rely on a water pumping system to clean away 1/7 magma unless you don't mind doing some digging afterwards.

[Skorpion]

1/7 magma hitting water WILL create obsidian. I've seen that happen when I messed up pressurising it and it overtopped onto the brook.

Obsidian farming is generally best acheived by dropping water on magma. Water's safer and easier to cope with, and you get a muddy floor at the end of it to grow tower-caps and plants on, after you clear the stone off.

[Chromie]

If you designate a pond over obsidian, one bucketful will not generate obsidian, it will just eliminate one unit of magma. I haven't tested the limits of this though.

I've done this (to clear away HFS magma), and it doesn't just remove one unit - it empties out the entire tile.

Huh. Adjacent magma flowing must have confused me then.

[Albedo]

When making obsidian, try to add water to magma, not the other way around.

It's a lot easier to clear away excess water then it is to get rid of extra magma.

The exception to this is if you are not farming obsidian but making something multiple layers deep - then you can layer one upon the other, back and forth, and create a thick block of obsidian to then carve as you wish. This is a classic "formed obsidian tower" method.

Additionally, if you add a measured amount of magma to the water, you will have very little left over - none if you drop it from a retracting bridge system over the target water, so the shapes match. (Or, at least, so there's no excess pouring in after.)

For those times that magma does exist, it's not difficult to have your dwarves only clear out the safe tiles until it evaporates.  A bit tedious, perhaps, but not difficult. 

[Jim Groovester]

If you designate a pond over obsidian, one bucketful will not generate obsidian, it will just eliminate one unit of magma. I haven't tested the limits of this though.

I've done this (to clear away HFS magma), and it doesn't just remove one unit - it empties out the entire tile.

No kidding? That's a handy trick to know.

[eerr]

for refrence, I was using a pump to push the water to the layer above the magma.

I would then either channel out the tiles/dig ramps in the level underneath.
(doors on both levels) and ignore the water inside the pit.


I also made a backup drain into the aquifer with floor bars over it.


I never ever let the water or magma go above 5/7.