Hi all!
So I've been tasked with making a mushroom cloud in Carrara; as in the explosion from a nuclear bomb.
I had a few theories about how to do it, but my ideas aren't working :(
For now I only need it for some still renders, but I have to do multiple views so the could can't be 2D.
My first approach was to model the cloud, but that's as far as I got. I'm not sure how to go about texturing it; I was thinking terrain shaders might do the trick, but I've been messing around for a while and my eye is starting to ache.
Any ideas guys?
Y'all rock!

I'd create it using multiple layered cloud elements inside each other.  Then use custom procedural shaders on each layer to simulate different light levels, colors and granularity.  This would also have the benefit of allowing you to modify each cloud layer and texture for the animated render.  Sorry, I can't be more specific, but I think you should make custom shaders.  The built ins just aren't designed for this kind of effect.

Quote - Hi all!
So I've been tasked with making a mushroom cloud in Carrara; as in the explosion from a nuclear bomb.
I had a few theories about how to do it, but my ideas aren't working :(
For now I only need it for some still renders, but I have to do multiple views so the could can't be 2D.
My first approach was to model the cloud, but that's as far as I got. I'm not sure how to go about texturing it; I was thinking terrain shaders might do the trick, but I've been messing around for a while and my eye is starting to ache.
Any ideas guys?
Y'all rock!

It's going to be tough with just the volumetric clouds, because there aren't any good deformers for them. The shape of a mushroom cloud can be divided into a column, a hemisphere with an upward bulge on the flat side, and a torus for the edges that sink as the outer edges cool. You might be able to simulate those shapes with one cloud for the column, one with a flat bottom for the top, and several small ones spread out at the edges for the rim sinking.

The Primivol plugin from Inagoni would probably get you closer to what you want. I haven't used it myself, but I hear great things about it. You should be able to do your basic shape with a simple model, then fill it with the cloud texture of that plug in.

Another possibility would be to use a particle system. Make a polygon mesh for your basic shape, with an alpha mask that makes it completely invisible. Set your particle emitter in the mesh, and constrain the particles to stay inside the mesh. A wispy, smoky image on a smal splat primitive (such as you might use for a plain column of smoke) might get you in the general neighborhood. It might even make sense to have two emitters, one for the column, and one to spew out particles from the top of the column out to the edges.

 Here is a quickie I did with a simply deformed sphere, a spline mushroom base object and a surface replicator. You can see the source object to the right of the cloud. The spline object has it's visibility turned off. You can expand the image if you want to see more.

This could be enhanced with a little more work on the alpha channel in the shader and possibly even a displacement map. In fact, there's a couple of more things that could be done with extra replicators and maps to control the replication that could add some cool detail. 

The problem with volumetric clouds is the render time and overlap issues where the clouds will render black instead of seamlessly merging. 

Enough procrastinating, back to work...

 I must not want to work today. Here's the same thing with a couple of shader and lighting tweaks. No post work. Carrara's a pretty tidy little package. :D

Awesome!
I appreciate the help guys; I might be gettin' somewhere now :)
I think my first mistake was to make the cloud one single mesh; the umbrella shape you're using Mark allows for a light source to be placed inside the cloud-that's cool!
I was going for a glow/displacement/alpha mix; I didn't think of just adding a light...duh!
Let me give this another try; stay tuned...

My bit of fun with the concept. Brian

 I don't get to play with bombs much! Here's a graphic novel type of A-bomb explosion.

Here's my first feeble attempt at Mark's approach... Still has a ways to go obviously; my handle on Carrara's shaders isn't as deep as it should be. Uh, let's see: Simple (hidden) cloud mesh with a squashed sphere distributed over it via a surface replicator. For the sphere shader: Simple gray color, Noise Factory alpha, turbulence displacement One high-intensity bulb in the middle. I guess this is a good place to start; suggestions? This is FUN!

Well done JT.
Brian

I also thought of the particle emitter method. (Actually it uses at least two, because you're bouncing one off the ground with a wide angle for the base shockwave while another one goes upwards.) But it's tricky as heck to get just right because of all the variables.  Involves having no or low negative gravity, just the right blur effect setting over an applied alpha image (because having actual clouds as a rendered particle object will kill your CPU and take way too long), low particle mass and high air friction, and some things involving particle lifespan in the shader (color and glow channels) to make the clouds look firey and violent... To be honest though, the particle emitter way is likely much more useful for animations where you want to see the cloud rising into the sky than doing something quick for a still image. (And it can look impressive if you manage to get it right, but it's not that easy.)

Gotta admit though, Mark's way is genius for achieving the effect quickly in still pics. No tweaking 500 times and guessing what shape the resulting particle cloud will take.

Paul: I don't know if I'd even wanna attempt this using particles; the complexity of the systems and the rendering times would be off the charts. If I end up needing to animate the cloud, I'll either try some After Effects trickery or try to composite it with Particle Illusion.
Mark: Sweet image! What kind of lighting did you use on the cloud?

 There is only one bulb tucked up in the cloud and a sunlight. I'll post the file up shortly and you can just download it and poke around. :D

You can download my Carrara scene ** here**. 

The original scene used DCG's Starbright for creating the background stars. I've removed that so that the scene is only using native capabilities. 

Have fun!

Thanks for sharing that Mark

Thanks-a-million Mark!
It's very insightful getting a look at all the clever tricks you have going on in this scene; I never would have thought of 'em :)
I really appreciate the help!
JT