This is my first post here. I am building jewelry components for creating different bracelet designs and have come upon a difficult material to replicate. We have several new bracelet designs that feature Cat’s Eye Beads and my efforts to successfully make a realistic material have fallen short. The effect essentially is similar to anisotropy, but the reflected light appears to come from inside the object. Would anybody be able to assist? Thank you!
Volumetric anisotropic reflections aren’t supported by cycles (and I don’t know of a renderer that does).
The best you can do is experiment with anisotropic reflection combined with either translucency or SSS to give the semi transparent base material with an anisotropic reflection.
To give it the appearance of depth - you could then overlay a glossy shader on top of this base material using the fresnel node to control the falloff.
Another possibility that seems to work - is to actually model the catseye accurately.
Cats eye looks the way it does because it has needle like micro structures within it which reflect the light anisotropically.
My idea is to use an inverted hair particle system. If you comb all the hairs into the interior of your sphere so that they all line up - then apply an anisotropic shader to the hair particle system - you get a volumetric anisotropic reflection. This technique could be used for any fibrous minerals.
Combining this approach with say the volumetric scatter and absorption would get you pretty close I think. I have done a couple of experiments and it seems to work in principle (finer more numerous hair would probably look better though).
One problem that I haven’t found a solution to is how to stop the hairs coming out the other side - ideally I only want to show hairs that are within the volume of the sphere - does anyone know if blender can cut hairs at a boundary (kinda like a boolean function for hair?). Obviously I can cut them manually - but it’s very time consuming.
That’s really an impressive result moony. And it would be awesome if someone could show me how to cut the hairs to truncate on a defined surface! In the past I have painstakingly cut each hair to length in the particle edit mode by placing a separate reference object and then zooming in close with the cut tool. Wouldn’t it be awesome if we could just make a surface (such as the opposite side of the sphere) the cut brush?!
Very impressive indeed, but I have to say, I’ve never even heard of such a phenomena before 
And I still can’t wrap my head around what is actually going on optically. Some interresting effects here, almost all were completely new to me:
That’s an interesting phenomena… and nice render moony! have you tried mixing the hair material and a transparent with ‘isTransmission Ray’ as a factor? it should render the hairs only inside a glass object.
and thanks for the link CarlG. It gave me lot’s of things to think about!
Thanks moony for your time and effort on this. I have yet to come up with a believable material yet, but your link to the retroreflective effect has me hopeful. I’ll post whatever I come up with.
Interesting appearch secrop.
I had a play and its quite a nice effect. I also found that if you replace the bottom Anisotropic shader with a glossy instead that has a roughness around 0.3 - you get a decent looking moonstone type effect from essentially the same node group.
Nice work.
it’s a fast way to fake some internal reflectancy. Not the best, for sure! it works ok with spherical objects, but others than that get’s kind of strange. At least it’s still a possible way to get this light interaction without some complicated volumetric shader yet to be writen…
After some experimenting with your setup Secrop, I realized it would not work for my application. One issue was the center of the bead would interfere with the reflections coming through. I gave the center of the bead a transparent material to combat that issue, but also found the reflections were opposite of what they should be. I am working on more of a physically accurate approach by using many filled curves, similar to the hairs moony tried, set just inside a separate glass object. The HDRI image I am using has a tree that breaks up the light source, so that is why there are two bands in my sample.
Hi,
I am goldsmith and lapidary.
I know that this is an old post but perhaps some of you are still on the forum.
I am new in blender and 3D and I want to render a star rose quartz in blender.
I understand the mecanism of chatoyancy and asterism and made test of modeling in blender but i don’t have as good result as yours.
I am at this point for the moment.
http://pasteall.org/blend/index.php?id=48494
And here is the hdri used for the project :
326-free-hdri-skies-com.hdr (5.5 MB)
I have a star effect on the rutile needles but it is very ligth when i put my quartz cab on it (layer : cabochon_vierge) it is worth. Do someone have a better solution to make star effect and keep transparency and refraction as on a star rose quartz cab.
To have a look of the type of rendering i want , here is the photo of a star rose quartz i made : https://www.facebook.com/qlemouland/photos/a.151702585007449/151702688340772/?type=3&theater
Here are explained the asterism in details : http://www.nordskip.com/rose.html
Thanks by advance for your help,
Quentin.
