Vray Blend Material Coat Material refraction seems to have no effect

[dennisqw]

Hi all, If I have a coat material with no reflection (color = black), and refraction at white with an ior of 1.0 shouldn't my coat material be invisible? This doesn't seem to be the case.
I've discovered this because my real goal is to make a coat material that will only add a specular highlight to the base material (maybe a little reflectivity as I know that comes with any highlights). Instead when the blend amount is set to white (100%) I get an image that looks the same as if there was no refraction.
I know that opacity can have an effect, but that shouldn't be necessary (and I can't really get that to do what I want in any case).
I guess another way of asking this is do the refraction settings have any effect on a coat material. It seems that it does not.

[vladimir_krastev]

Hi, thanks for posting.

my real goal is to make a coat material that will only add a specular highlight to the base material

You could copy the same material as coat and manipulate it's reflective settings.
For example here I've removed the reflection texture and applied colour and glossiness

[dennisqw]

Thanx for your suggestion. It seems a little counter-intuitive to me but makes sense. Unfortunately, it actually won't help me out, and my fault for not including more information in my original question. In that question I was trying to keep it a little more theoretical, because I still don't understand why perfectly clear refraction, no IOR doesn't do what it should. But in any event the reason why I need a beefier reflective highlight in the first place is that my base material is fastSSS2. Although it might be possible to get the highlight I want in that material alone I couldn't figure it out, so that's when I figured I could just add it as a coat layer. So even though your suggestion would work under normal circumstances it wouldn't work here. Any other ideas?

[vladimir_krastev]

Hi, in this case could you share an example of your progress so far and your SSS material settings? If you could setup a simple scene that shows your issue this will be best.

[dennisqw]

Thank-you for your help. I'm uploading the scene along with a render of it. So the teapot on the left is just the SSS material. It looks as expected, it distorts somewhat the background and doesn't have much of a highlight. The teapot on the right is just the regular material with some reflection and the refraction set to1. The teapot is transparent to the background and only shows the highlight. The teapot in the middle is the problem. It has the SSS as the base material and the regular material as the coat. As far as I understand, it should like the one on the left, with the highlight from the right, as theoretically the coat should be transparent to the base, not to the background. (Go to frame 2 to get the same camera framing)

[fixeighted]

Try this version - maybe it's a suitable workaround.

The main difference is using the shellac mode, then tweak the reflections etc., to match your ideal mix.

[dennisqw]

fixeighted I opened your file, and don't see where you used shellac mode. The materials all look the same as before. I did explore that earlier but it didn't give me the results I wanted, but I can look into it again. Thanx for looking into it though. --ds

[fixeighted]

Oops...not sure what happened there but here is an update.

The new texture is to ensure a better comparison of the refraction.

Basic idea is that the coat needs no refraction and only a tiny bit of reflection, boosted by its IOR and set to shellac, which appears to give the required effect.
Maybe that works for you...it is the only method I could think of at the time

[vladimir_krastev]

Hi, what about manipulating the sss parameters? For example if we compare your material to the build in marble (since it is highly glossy) your material differs a lot in these:


All of these parameters reduce the reflectivity of the material. Is there a specific reason for that?

[dennisqw]

vladimir Yes, I understand your question. What I am making is a translucent plastic that gets more opaque as it gets thicker, but it's also fairly reflective. and it also doesn't have much of an IOR. It seems that the SSS2 would be ideal for that, and indeed what I have is just right except it needs some boosting on the reflective highlight. That left teapot looks just like what I want, I just want to add the highlight from the right one. So doing what you suggest I change would be great for marble but not this. The easiest solution is the coat, for which I still remain confused as to why that doesn't work like it should. This seems like a flaw in the programming in any case. And I can imagine other circumstances where I would want the coat to work in this same way.

fixeighted Thank-you for your efforts to continue to work on this for me. From the picture it does look like you came pretty darn close, closer than I could. I'll open the file and try to see what you did. It might get me through this project, but it still doesn't seem like the "correct" way to do this, so I'm hoping that vray central will be able to get to the bottom of it for me.

edit, so it does seem like shellac mode is the way to go. Maybe that was created to avoid the problem I'm having, or maybe it's just a workaround, but in either case I think I can move forward with this. The trick as I see now is to turn refraction to black which I wouldn't have thought of but now kinds of makes sense. (hopefully it will work in my more complicated real scene ) Thanx for your help.

[fixeighted]

No problem with trying this as it's always fun.

Anyway, you needed a way to simply add over the highlight onto your SSS shader, which is exactly what my version does.

Effectively, using the shellac acts like an add function, as it doesn't use any refraction but only the reflection which you can tweak to your liking using the IOR and actual reflection amount.

[dennisqw]