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[Doomshifter]

I simply cannot find a straight answer for this with the search function.

Say, perhaps, I wished to make a huge obsidian-cast rectangular prism. Utterly massive. Say, for instance, I knew absolutely nothing more about this than the fact that I need water and magma. Would there be one among you fine ladies and gentlemen willing to explain, from start to finish, how to obsidian cast?

Any help whatsoever would be greatly appreciated.

[Retro]

I've always been a bit confused about this myself, having never really given it a shot and finding all explanations to be a bit confusing. I think I've started to wrap my head around it, though - someone's probably definitely going to have to correct me on this, but this is how I understand it to work:

- Build the walls of the cast as a square-based prism up as high as you like - easier to just mine it out later if you want fancy shapes. Extend the prism shell 1z higher than you want the cast to go.
- Build a bridge/group of bridges along the top z-level of the shell and pump magma up to it. Fill the bridge with enough magma to make it flooded 2/7 and 3/7 or so.
- Using a pump stack up to the second-highest z-level, pump water into the shell. Fill it up to 2/7 or 3/7 along the bottom level of the prism, then shut it off.
- Drop the bridges, colliding the magma with the water.
- Shut the bridges, prep more magma, and cover the lowest empty layer of the shell in water again, now on top of the obsidian walls at the bottom.

If I'm right about this, should work just fine so long as you're magma-safe. Just deconstruct afterwards.

DF pros: Am I close enough? I imagine there's a few ways of going about it.

[Doomshifter]

Thanks Retro. I foresee much Fun, as the last time I tried to use a pump-stack I managed to burn the axle powering one and flood everything with magma.

EDIT: Fun with a capital 'F' for 'Flame-related injuries and deaths'.

[Asmodeous]

You can fill it full if you want, you just don't need to. In fact 1/7 will work fine if they don't evaporate before contact.

I turning a whole magma pool into obsidian one level at a time just by dumping a river into it with a 1-tile wide pipe that I would shut off as each layer finished.

[bmaczero]

I think Retro has the basic idea.  Points to empasize:

The cast needs to be a chamber 3z tall.  You'll have a bottom level where the reaction takes place with access doors for hauling away the obsidian, a middle level with access doors so miners can get in to channel out the obsidian, and a top level where the water (or lava, AFAIK it doesn't matter whether you add the lava to the water or vice-versa) can be spread out on bridges before being dumped evenly over the bottom layer, which you fill with the other substance.

If you want to minimize flame-related Fun (why would you want to do that?) you can put the magma on the bottom level and dump water onto it, that's how it's usually done, though I don't see that it matters much.

The wiki has a pretty good article on it.

[Grendus]

There are several ways to cast obsidian.

No matter what, you need a mold. Although you can pour magma over the water, you really want to pour water over the magma. You usually end up with excess on the top, and excess magma is more dangerous (and more Fun^tm) than water. Fill the mold with one liquid, then pour a layer of the other on top.

The more hectic but easier way is to fill one layer of the mold with water/magma then pump the other fluid over it until you have a solid layer of obsidian. This leaves a lot of mess, but it requires less construction. If you alternate liquids, you can build very quickly. You have to be careful though,  it's easy to end up with pockets of magma or water if you don't watch it.

The safer, less dwarfy way is to use a bridge pattern above the mold to drop one liquid onto the other. This removes the problems with excess, and in terms of casting doesn't take much longer, but it's less overhead intensive. It requires a ton more mechanisms though, and requires you start with a larger mold than you would normally.

[WumpusKing]

I think Retro has the basic idea.  Points to empasize:

The cast needs to be a chamber 3z tall.  You'll have a bottom level where the reaction takes place with access doors for hauling away the obsidian, a middle level with access doors so miners can get in to channel out the obsidian, and a top level where the water (or lava, AFAIK it doesn't matter whether you add the lava to the water or vice-versa) can be spread out on bridges before being dumped evenly over the bottom layer, which you fill with the other substance.

If you want to minimize flame-related Fun (why would you want to do that?) you can put the magma on the bottom level and dump water onto it, that's how it's usually done, though I don't see that it matters much.

The wiki has a pretty good article on it.

I think doomshifter is trying to make an obsidian tower. Take the method but just start higher and do it one layer at a time.

Like

pump magma, let it fall to bottom floor; turn it off
pump water, and then it turns into obsidian; turn it off
repeat

Use bridges if you want.

[Arrkhal]

The more hectic but easier way is to fill one layer of the mold with water/magma then pump the other fluid over it until you have a solid layer of obsidian. This leaves a lot of mess, but it requires less construction.

That's what I do.  If I'm trying to preserve dwarven life, I typically will build up the pump stack one pump at a time, so that an overflow is impossible.

[Misterstone]

I started to do this myself on a large scale once, and posted about it here:

http://www.bay12games.com/forum/index.php?topic=16443.15

Like the other said, it works better to pump in lava (one Z layer at a time) then pour water on it.  If the magma is more than one Z layer, only the top layer will form obsidian, and the bottom layers will be full of magma.  Then again, there could be fun (tm) uses for this!

Eventually I got bored and stopped working on it (I have a short attention span).  The main flaw I made was, the pumps that moved the lava were _inside_ the cast, but they ideally should have been on the side of the cast.  Yeah, pretty stupid planning on my part.  If you do this with a much smaller area it would probably go much more quickly.

[Bauglir]

-snip-

[Arrkhal]

After typing all that, I just remembered how pump stacks ACTUALLY work, so I think you'd need two stacks alternating the z-layers they fill, and if you don't want to go to the trouble of setting up two different sources for each pump stack, you'll need 4 stacks total, 2 for each magma and water.

Not really.  The pump that faces away just needs a short little tunnel to reroute the liquid into the mold.  Then you just build a wall so the liquid goes up to the next pump, once the tunnel is safe.

[Quietust]

My last fortress involved obsidian casting - see "Rhymestakes" on DFMA, particularly year 309. My method involved simply pouring alternating layers of water and magma into the mold, switching each time I formed a solid layer of obsidian. The very top layer required a bit of additional trickery, as I had to construct a bunch of raising bridges along the top in order to hold in the final layer of water.

[Bauglir]

-snip-

[Grendus]

After typing all that, I just remembered how pump stacks ACTUALLY work, so I think you'd need two stacks alternating the z-layers they fill, and if you don't want to go to the trouble of setting up two different sources for each pump stack, you'll need 4 stacks total, 2 for each magma and water.

Not really.  The pump that faces away just needs a short little tunnel to reroute the liquid into the mold.  Then you just build a wall so the liquid goes up to the next pump, once the tunnel is safe.

Good point. You'd want to wall the sucker in for safety's sake, anyway. So you can probably actually skip the floors you're going to deconstruct and just build your gear assembly stacks from the tops of the walls one layer down.

EDIT: and since every other pump is going to be submerged in magma, you'll want magma safe pumps and gear assemblies (because the magma will flood that region of the stack, I believe).

Depends on your design. Personally, I use magma proof pumps anyways. Iron is easy to come by (in dig deeper, steel is too if you're tough enough), an if you have garnierite there's nothing better to do with it. Plus, I've had designs that shouldn't have had magma problems get a little magma splash and go to pieces, using iron, nickel, and bauxite is both easier and safer.

[Skorpion]

Personally, I'd build one level at once with constructions, and cast inside it by pumping first magma and then water in via pump stack.

Water being water, you could probably use the same resevoir and pump for the whole thing if you mount it high enough.