Dichroic Glass

[cg_Butler]

Hi all,

 

It's been a while since i've posted on here but I have a question regarding a certain type of glass. Dichroic to be specific.

 

check out some examples here. http://lmgtfy.com/?q=architectural+dichroic+glass It seems in the material sample I have been sent that the shadow colour is different from the diffuse colour and n some examples in a google search ths s also the case.

 

I have no problem creating it to look correct for diffuse, reflection etc, but a different shadow colour I cannot seem to do. It might have to be a post production job.

 

I was wondering if anyone's had to create a similar glass material that has a different shadow colour to its diffuse colour. Lets say cyan/blue diffuse but magenta/purple shadows?

 

Thanks in advance.

Edited September 6, 2016 by cg_Butler

[Chris MacDonald]

I have an idea, give me a while to test it.

[cg_Butler]

Thanks Chris.

 

Just FYI, I have faked it by duplicating the object and applying a glass with a purple tone so the shadows are purple. Hidden it from rendering, and made the blue one not cast shadows. I hope that makes sense.

 

But i'd be interested in seeing if it's somehow possible to do it all in one material, although i don't think that's possible in VRay.

 

Good luck pal!

[Chris MacDonald]

Yeah. I've got reasonably close in so much as I've got a glass material that changes colour based on the direction that light is hitting it, but VRay doesn't currently allow you to map the exit colour - which would be ideal, as I could use the same map and just shift the colour 180 degrees using a colour correction map.

 

That said, I'm not entirely sure ALL dichroic glass exhibits a different shadow colour to the colour of the glass itself.

 

Perhaps it might be worth giving the Thin Film OSL shader that Vlado produced a go

 

It would certainly make it a lot easier than using map within map to create the effect.

[cg_Butler]

Sounds very similar to my setup.

 

I agree that not all dichroic glasses change the shadow colour, but the one I've been spec'd clearly does! I think I'll stick to the "cheat" that I've got as it looks very convincing. I'm not sure mapping the exit colour would work, as it might make the glass appear different as i think you'd have to lower the max depth to get the colour to show and that would make the diffuse colour wrong too. Mapping the shadow colour a material gives would be what I want!

 

I love having these little gems to figure out. Although my brain is hurting having been on holiday for a week. It's tough to jump straight back in to these kind of problems! thanks for taking a look mate. Much obliged.

[Nicolai Bongard]

Probably not what you are after, but the first thing that comes to mind is that you could perhaps use the shadow render element and use that as a mask in Photoshop for a color adjustment, if faking it is good enough.

[cg_Butler]

Thanks Nicolai.

 

It's an option for sure but i always try and do as little post as possible and try and be technically correct. It's highly likely that this sort of thing will have to be tweaked in post so I will use the shadow pass where necessary. thank you.

[Nicolai Bongard]

Depending on your scene, perhaps you could get away with having the original lights exluding the surface the shadow of the glass comes onto, and then placing/duplicating the lights and change the color and have them only affect the surface where the shadows are. Then their illumination would look like the color you want? Obviously this is still a fake way of doing it though, and it may not work depending on how your scene is.

 

Since this effect is something that should be possible to recreate, perhaps try to ask on the chaosgroup forums to see if they have a clever way of doing it.