top 5 fake stone tips...

[inkydigit]

fake stones can be difficult to get looking right (especially displacements), I am fishing for any tips that you care to share, I am not really looking for clip files, but descriptions and explanations, though clip files may be useful in some cases!!!

I have sometimes used voronoi displacements to break up the regularity of the shape of the stones, but this does not always translate easily when scaling up or down....

[Hetzen]

I'll be interested in what people chime in with. Can't say I've really got to grips with the shader.

Something that's quite effective, is to put a subtle amount of reflectivity on, depending how dry you want them. Something like 0.3 or less.

[inkydigit]

Hetzen, definitely!... some specularity can work wonders in adding 'realism'...

[Esgalachoir]

I've been trying to make more realistic looking rocks myself, and I've discovered that if you use some clamped perlin noise as a negative displacement on top of a single power fractal, you can get a nice "pockmark" effect.  Basically, you set up your perlin noise, adjust the color with a color adjust shader until you have little white dots, then adjust the scale to your taste.  It looks better if you have multiple layers of this kind of noise at multiple scales each with different levels of displacements.  I imagine that with some smart blending you can make some pretty interesting patterns, similar to certain types of volcanic rocks.  It would probably look nice on asteroids as well on a larger scale instead of your regular crater shader.
You don't want the initial power fractal too noisy, or else you lose the pockmark effect in the pattern...
I was trying to make large chunks of obsidian in this image here(It needs some more work when I can get to it)...but you can see the eroded effect the pockmarks give...
One more thing, I'm not entirely sure if this effect occurs in obsidian 

[inkydigit]

thanks Esgalachoir, interesting technique, definately possible to get some nice porous lava type stones, and obsidian is definately not porous, more like glass!
cheers
Jason

[Henry Blewer]

I set up the fake stones using a separate surface layer. Normally I use the same colors as the rock faces on the basic terrain. The smallest details are closest to the surface layers inputs for color and displacement. I match the scales yo the size of the fake stones 'group' (consisting of several scale sizes from group A, 0.1 to 1; then group B, 2 to 10, etc.)

If a blend by shader at the bottom of the fake stone node is used, keep the fuzzy zone large. This avoids 'exploding' stones.

[FrankB]

one things that works great for me as a starting point is to create a displacement on the stone in the following way:
- feature scale = 1/3 of the stone size
- largest scale = stone ssize
- smalles scale = 1 cm, or if the stone is less than 10cm, I go into millimeter scale (but it can give problems in renders potentially)
- displacement = 1/6 of the stone scale
- noise type = perlin ridges, although the perlin mixes work well too

So this is a starting point, but it's easy to tweak things from there.

Regards,
Frank

[inkydigit]

thanks njeneb and Frank....very useful!