Glass, edges and IOR confusion

[branskyj]

Hi all,

3DS Max and VRay user. Here is my scene- spiral staircase made of glass segments. Each glass segment has chamfered edges and thickness of 0.8cm.

My glass material:

diffuse color- almost completely black 0,0,5

reflection- 128,128,128 and falloff ticked.

refraction-250,250,250

no bump, no distortion.

If I apply an IOR of 1.517 to the refraction slot of the glass material the chamfered edges become well pronounced with dark finish which is exactly what I want. The problem is that the 1.517 IOR makes what is behind the whole glass segment all horribly distorted.

 

If I apply an IOR of 1.002 to the glass material I get the opposite- the edges of each glass segment get completely lost and the dark finish goes away since there is no light refraction happening inside the glass. But at least there is no to minimum distortion after each glass panel which is what I am trying to achieve.

 

In general I am confused as to what IOR for glass should I use when I have glass with thickness (box object) and also what IOR for glass with no thickness (plane object).

 

Thanks for any help.

Edited May 27, 2013 by branskyj

[Ismael]

Here is a beautiful reference, http://www.cgarchitect.com/2013/05/brentwood-luxury-residence

[Stephen Thomas]

If you want the glass to show up darker when viewed on the edge then you don't want to go for a pure white refraction colour. The whole point is that the thicker the glass the more diffuse colour shows up and the less you can see through it, so you need some falloff. For glass I normally use a black diffuse, pure white reflection with fresnel and an rgb of 100,5,240 in the refraction, affect shadows on.

 

This will give you a greenish tint which affects any light passing through the glass and should give you the edge definition you're looking for. You can increase the saturation and decrease the value of the refraction colour to increase this effect. If your IOR is making things look weird then just drop the refraction IOR to 1.0. Make sure to keep the reflection IOR around 1.6 though.

[Chris MacDonald]

The dark edges of glass are caused by total internal reflection/refraction, and what you are seeing is all the way through the long part of the glass with light being absorbed as it travels through it (Hence it being so dark). The often green hue/tint to this is caused by small amounts of iron impurities within the glass.

 

If you are after realism I wouldn't add a colour to the reflection or refraction - as this isn't what happens in real life.

 

The way to approach this realistically is to use the fog colour, as it is "thickness dependant" i.e. it will let light through the thin part of the glass but not as much through thicker parts of the glass.

 

I would start with the settings for a standard/photoreal glass such as this;

 

Pure black diffuse

Pure white reflection

Pure white refraction

Fresnel reflections with an IOR between 1.5 and 1.6

 

This should give you a pretty solid glass base from which to work from. Now would be the time to start playing around with the fog colour to introduce the dark green tint at the edges. It might be worth taking the fog multiplier down to a tenth, or even hundredth otherwise it will be very sensitive to any adjustments you make to the colour.

 

The bias controls the "falloff" point between the thick & thin parts of the glass, for lack of better words. Generally speaking though I never really need to adjust this.

 

Once you've done this you should have some pretty nice looking, physically based glass.

Edited May 28, 2013 by Macker

[notamondayfan]

Before getting stuck into the details of materials, check your geometry is correct. It should have a thickness, no open polys. Also be careful with smoothing groups. To test, remove smoothing groups, and see if you're still getting a distorted image.

 

Dean

[Ernest Burden III]

Also check normals, make sure there aren't doubled polys. Since I rarely do things the 'correct' way, one cheat I use is to separate the edge polys from the 'plane' polys, so I can use a different material on them. That way I make the clear parts look the way I want, and can mess with the edges on their own. Sure, a proper 'physically correct' material should handle both beautifully, but I like the extra artistic control.

[branskyj]

Sorry for the late response (work,work, work) and thank you far all the help, guys.

Well, I feel silly now- as it turns out normals were fine but I had to clear the smoothing groups of each glass panel and that did the trick.

Now my edges are well pronounced and black and there is no distortion in the glass.

Thanks for all advice and tips.

Have a good week.