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Anyone have an idea of how to go about making a marble material that has some subtle SSS, as well as deep refractive cracks? In other words, cracks that you couldn't feel with your finger, but would perceive visually? Polished marble tends to have cracks that you can see but not feel.

Render time is not a concern, hit me with your most contrived solutions...

(My hunch was a simple 2-layer material: color on BSDF #1 and transparent glossy BSDF #2 with a deep normal map for the cracks? Then turn on SSS for #2?)

You can do volumetric cracks using geo which is only visible to refl/refract. That geo needs a special mxm which is just a coating with the bsdf turned off. Tom's idea originally.



And you can try texturing the trans of your sss, but you wont get truly veiny volumetric effect thats impossible. The first image uses normal maps on the metallic flakes which helps them look submerged, esp for animation.

Eric, thanks for the response, very helpful. Unfortunately I can't model in any cracks. This particular project requires the reproduction of a real-world marble from a vendor. The resultant renders will be used basically as "preview" or demonstration images, shown to potential buyers, to give them an idea of what the finished sculpture would look like. As such I need to be able to tweak and/or move around the cracks on the fly, so that we can fine-tune it to get it looking accurate.

Here's my start so far, without SSS. As you can see, the cracks are extremely unconvincing. They look more like soft stone cracks than marble veins. EDIT: image has been overwritten, no longer relevant


If you're feeling tremendously helpful, here's my MXM package:
https://dl.dropbox.com/u/2569505/Pink_Marble.rar

Thanks again for the advice.
P.S. - I couldn't find your normal-mapped flaky material in the resources database, would you mind making it available for me to reference for my own material?

using geo which is only visible to refl/refract

Because of that you dont need to boolean just overlap the geos, so not much modelling.

I'm sure your client would be happy with a photo-textured mxm, normal maps manipulate the surface normals so cant help with volumetric veins / cracks.

Put the same texture in trans slot with default sss, and set assym to -.5 or thereabouts, that should do it, but it depends on the mapping too.

eric nixon wrote:

using geo which is only visible to refl/refract

Because of that you dont need to boolean just overlap the geos, so not much modelling.

I'm sure your client would be happy with a photo-textured mxm, normal maps manipulate the surface normals so cant help with volumetric veins / cracks.

Put the same texture in trans slot with default sss, and set assym to -.5 or thereabouts, that should do it, but it depends on the mapping too.

This is great.
Just a question, when you say overlap geometry you mean that you are completely modelling every piece as "joined" (so you have 2 faces overlapping but with opposed normals)?
And just this overlapping parts has got what only refl/refract material?

Thank you,
Rickyx

No.. cracks are single sided geo..., Its just that you dont need to worry about modelling cracks to fit the geo, the thin bumby 'crack' geo just has to intersect the transparent object, then it becomes a visible crack.. you see.

So you can animate the cracks if you want...

And Ricky there are no 'pieces', the visible transparent object remains unmodified.. which makes this quite useable.

To all: For a general guide to faking marble veins, this mxm is a good start.



EDIT:fixed the link
http://www.mediafire.com/?6vcx7q99dkid9z1

I'm having at go at what I recommended (only fair ), and so far so good, heres a wire. I used a voroni fracture to model a honeycomb core (shown in white), but I'm also testing the crack technique, in the screenshot this is the lumpy plane geo.



sl13;


one more sl17;

Awesome Work Eric!

I wouldn't bother with the honeycombe, its slowing down the render too much, perhaps a few submerged pieces near the surface is enough..

honeycombe is creating those dark marble flecks in this render, (doesnt have to be dark, could be any colour)

So yeah beware the honeycombe thingy is very inefficient, 'dont try it at home kids'

However the white crack technique is quite useable (I ended up with a live boolean so its still animatable, but doesnt show up in the marbles topcoat reflection), I just made it hidden to cam in case it intersects the surface due to the displacement...

Brilliant, this is materials beastery

wow brillant really!!
Is it possible to share this mxm Eric?

thanks a lot

The marble is nothing special, just 1 bsdf, and the Vein.mxm can be made in many ways, the key is that it doesnt have transparency and is single sided geo.

vein;

thanks eric for the detail