What is the scientific name of that colored rough gloss in some materials.

What is the scientific name of colored rough gloss in materials ?

I am not a scientist in materials, but I think to see in some materials a rough colored gloss, like in satin, sports-wear, fabric for tent, hair, fibers, and maybe some stones, pearls, shells, skin, fish.

I make those with a diffuse shader ( = already rough glossy , right?), with a rough glossy ( 0.3 roughness) colored without Fresnel ( anyway if I should put Fresnel here, Fresnel effect almost disappears ? ). And on top of that I put a colorless, sharper reflection which has than Fresnel.

I used to call it metallicness, but I suppose that is a wrong name. So what is that rough colored gloss I think to see in those materials ?

Often we talk about the translucency, transparency, etc of a material, but this colored-rough-gloss property, I don’t see people talking about it.

gloss reflections

but if you want more control then use the PBR nodes setup
gives a more physically correct set up!

happy cl

Reference pictures would be helpful to understand what you’re referring to. Something like what I’m attaching below? Shiny fabric like this or satin is IMO particularly hard because the visual qualities are created by very small surface textures that are hard to simulate correctly with bump or normal maps. For satin, I’ve had some success with mixing anisotropic glossy shaders. In fact I would guess that a lot of what you’re referring to (hair for instance) is similar to anisotropy. Which basically just means that the reflection is stronger in one direction than another.

Attachments


Iridescence?

All dielectric materials have non colored gloss (meaning, white reflections). Only metals have colored reflections (so copper or gold will tint reflections). You can have glass with powdered metal embedded in it (or on it), or mixed into paint (flecks in typical car paint).

Iridescence is an effect seen in some (very few) materials (found in nature but also pearlescent paint), but you can’t make these in Cycles (excluding the hack or fake attempts which also I have been toying with).

For basically 99% of dielectric materials, just stick with white. You may find materials which allows tint influence in center (Disney iirc?), but I’m not sure if you would use this to simulate real materials or fake some other stuff.

@RickyBlender: Gloss reflections could also refer to the coating right? I am looking for a name specific for rough colored gloss with or without pbr fresnel. On my materials I put at the end the pbr fresnell coating or reflections which are colorless and often sharper.

@Spiderbrigade:
Yes I attach here some examples below. Mhh, anisotrophic glossy shaders, and what color do you give them, and do you put a coating on top? Here I attach a node setup for sand in this case. ( Maybe a bad example because sand doesn’t have much of that rough-colored-glossy-without-fresnell. ) But anyway, this is a basic nodesetup for materials I will use.
There is a glossfix node that is to correct the rough gloss. It looks more like the diffuse this way. ( I preffer to put Ashikmin to CGX).

@IkariShinji: Iridescence ? Hmm, I will dive into that. As far as I know it has some similarities with what I mean. Might be interesting.

stc=1stc=1stc=1

I forgot where I got the glossfix node got from, somewhere here on BA.

Interesting, and that is what I read in most post or articles, but find it hard to agree with. I wonder, Satin is not a metallic, but why does it look so metallic? Right now I am looking at my satin curtains, and see there the white reflections, but also clearly ( I think) that rough colored gloss which looks metallic. And also when we look at the hair BSDF in Cycles ( reflections) we see that it is using a gloss, and we color it. ( I used to put a non colored gloss on top of it ).

Gloss has to do with lamps specular reflections
or from HDRI maps

like some metals have a different colors function of angle of light rays

happy bl

Thanks for posting images. What you’re referring to is definitely caused by micro-textures of various kinds. Look at the satin image you posted - the “RCGWF” has a definite structure to it caused by the fabric weave. The cloth threads present a complex surface for the light to bounce off of. Technically, fresnel is still happening here, but the micro-scale normals are not the same as the overall surface normal so the light goes off in different directions.

This effect is at the core of how Cycles (or any other renderer really) approximates roughness in the glossy shader. There are many techniques for approximating this mathematically with different strengths and weaknesses. The plain glossy shader approximates a surface with random microtexture. The anisotropic shader tries to model something with linear microfeatures which is why it’s used for brushed metal (tiny ridges) or cloth (fibers/threads). The velvet shader assumes a very specific kind of texture based on some measurements of actual velvet.

The problem is that it’s non-trivial to adjust the quality of the hypothetical surface since it’s a statistical model of how light rays will bounce. It’s possible to get close using a very small texture (image or procedural) as a bump/normal, but there are problems with this as well. Basically the shader ignores any generated normals that face away from the camera so you get black spots.

Satin tends to look metallic because of the particular way the fibers reflect. Basically what you get is a reflection that is still quite rough due to lots of micro-bounces (you can’t see your face in a a piece of satin!) but looks sharp because it has strong edges where the fabric curves away. I’m attaching an older satin image using bump and anisotropy which somewhat shows this. When I’m at my blender machine I will try to do some more examples.

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@spiderbrigade:
Thank you for your detailed explanation. ( I am sure I have to read it a few times more later on).

I think that is it! The light bounces in the microstructure which causes the reflection to color. Right after reading this, I tried to simulate this in blender, but failed. A picture is attached.
1st shows the original sphere with it’s pbr reflection ( but with a bit high base reflection to see it better) .
2nd sphere shows a bump (distorted wave with a very high scale), and I expected to see then some rough colored gloss. It turned out to be rough, not colored; Overal the gloss has still the same color.
3nd spere shows a bump and rougher gloss. Also the gloss has still the same color.
I did this test with 16 glossy bounces, 8 diffuse. But didn’t make any difference.

Also a diagram of why I think that the gloss should be colored after an internal bounce. So that didn’t work. I am not sure if it is a limitation of cycles at the moment, or that my theory is not good.

So for now, I will still mix in some colored-rough-gloss when making things like satin despite the theory that a material is or dielectric or a metal.

I had that problem with the black artifacts before with bumpmaps, but thanks to Ace Dragon’s modbump node, the artifacts are reduced. What is does I think is that it reduces the strength of the normals facing away from the camera.

PS:In your picture I see the two kinds of reflections: On top the colorless pbr reflection, and on the front-left the colored glossy. How did you make that gloss on the front left? Did you gave the gloss shader some color?

stc=1

did u look at video on PBR from blenderguru
it gives a good description of this phenomenon

but does not really touch aniso and fibers or hair

happy bl

@RickyBlender

Yes, actually I am using cynicat pro’s reflection nodes. I tried the guru’s shader, but I am not happy the with it’s way to control roughness and reflections.
So I stick with the cynicat’s original node setup. As far as I understand it is mainly for correcting the fresnel at different roughnes levels. ( The rougher the less fresnel effect. That is pretty much it). On top of that I use the modbump by Ace Dragon, the glossy fix, and sometimes I need the IOR flip from Greg Zaal to make materials double sided with the same material.

If you know a way to make satin in Cycles with a pbr approach ( dielectric material), let me know. I doubt if it is possible in cycles to make satin without using a colored rough glossy shader, which is in conflict with the theory that a material is dielectric or a metal.

I did get one PBR nodes for fabric
but did not have time to test it

did you ?

happy cl

@RickyBlender

Yes I’ve seen a PBR fabric shader after I worked for a week on my own pbr fabric shader, but I find my pbr fabric shader much more complete.
The PBR fabric shader you have seen uses a velvet shader which IMO is not very complete; it is just a diffuse shader and it makes a black spot at facing angle.
My eye says that velvet is indeed getting darker, but not in the way the velvet shader does. What IMO happens instead is that at grazing angles the edges are less saturated. And less saturated implies that the edges are lighter, which implies that the facing angle is darker. So additional I made some nodes where you can adjust the color of the grazing angle. ( make it less saturated. ) My theoretical explaination is that a) at facing angle you see the light bouncing between the hairs which have a color and therefore you see that the reflections are colored, or b) you see at grazing angle more the end of the hairs. The hairs are thinner at the end and so you see less color whereas at facing angle you see the thicker parts of the hair and so you see more color.

Then I am using a rough colored gloss of which I am convinced it is a property of fabric; in the hair BSDF you’ll see that it consists of a glossy shader. ( assing the hair reflection node to a plane and play with the roughness). So the idea of rough colored gloss as property of a dielectric material is not that grazy unless hair is a metallic.

In addition I use a glossy fix node to solve a problem with rough glossy, a modbump node to solve problems with normals ( without that how can we speak of PBR?), and an IOR flip so I don’t have to solidify my fabric and I see the fabric at the backface the same as the front face.

That PBR fabric shader doesn’t use all that.
Here two screenshots of my fabric pbr shader: stc=1stc=1

that is getting crazy !LOL

are you going to share file
may be on blendswap
wish this was integrated in cycles !

but this should take more time to do all the calculations!

happy cl

I uploaded my latest version of the fabric shader v6a on dropbox:

You have to use colorramps for the roughness map and reflection map ( best to put the output of the colorramp first in an emission shader so that works fast). Important for me is that I give the holes in the fabric ( usually black parts) no reflection at all, then your fabric looks quite good at grazing angle as well. With contrast I make the black little holes even more darker.
I rarely like others node setup, especially without manual, so I expect you will experience the same. If I have time I will make a little manual for it. Hope you like it anyway. ( you have to append the material, because the scene is very empty. Nothing inside)

I little busy with a contract right now
but I will try to test it this weekend

and looking forward to test this

thanks for sharing

happy cl

@CarlG

Oh my… that thread about iridescence and diffraction is very interesting, but very complicated. My jaw dropped a few times. Interesting are also Disney’s notes about fabric; Specular tint at grazing angles, more gain at grazing angles, stronger fresnel peak

You are completely right: We are not modelling atom by atom in blender, so we have to approximate. Or what is the use of a skin shader when we don’t model the bones and the veins. I think I got your point there.

Eh yes, Someone said on blender exchange “cycles is physically correct, tweak your node setup”. If Cycles was physically correct I could do the double slit experiment. I really tried it once, but failed ofcourse. The pinhole camera experiment on the other hand was succesfull.

You write “My own disney approach …”. Do you have it somewhere downloadable? Might be something for my toolset. :smiley:

Well, I realize it is getting a bit complicated. So far I think I have to be happy what I got so far.
In my last setup I tried to implement Disney’s note “Specular tint at grazing angles” and “more gain at grazing angles”.

stc=1

I finally found the answer. Below the render shows real geometrie, not a bumpmap. The material is pure dielectric but looks metallic. The reason is that the light is bouncing in the ridges and the reflections take over the color of the diffuse before it reaches the camera. I tried it with a bumpmap as I showed before, but the light is not bouncing in a bumpmap in cycles. So if we make fabric I think we have to cheat by using a rough colored gloss.
stc=1

Had a longer answer, but had a crash due a partially crashed disk. Here is the short version:
No, sorry, was never uploaded anywhere because I couldn’t make it work with a wetting system I was also working on (loosely based on these ideas). It failed due to using real fresnel that gave me unmanageable/unpredictable outputs. Facing^5 as in newer PBR approaches would have fixed that I believe. I was about to grab a screenshot of it, to show the basic of the thinking, but machine crashed as I tried to start Blender - which evidently is on a bad place on a bad disk.

Also it doesn’t look organized enough to be “presented”, and I suspect due to it’s complexity it wouldn’t be as efficient as I would have wanted it to be. It’s basically my own idea of a “limited ubershader” (limited since it didn’t deal at all with refraction/transparent shaders).

Besides, setting it up for yourself is a lot more fun - and frustrating :smiley: - than looking at other stuff. It’s basically just some tricky mixing of different shaders with consideration to slider precedence and how everthing is hooked up together.