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Welcome to Rendering Tutorial site. This site is develop to help artist, architects, advertisers, visual artists and hobbyist a place to share, gain and learn from tutorial writers, important knowledge, tricks and tips in using rendering and image processing software. Some of the link here were cross posted from other sites, some of them were develop for this site, and some of them were shared wholeheartedly by different individuals.

Monday, 19 December 2011

Fog Bias_Vray Glass

Playing with the material editor: Posted by

The scene is just a Torus Knot object with V-Ray Sun + Sky. Nothing more.
Here a screenshot to show you how I set this material:

I used the classic V-Ray glass simulation, adding a touch of  ”negative fog bias” .
« Ohh Ciro, wow… it’s amazing! But…what does it mean “Negative fog bias” ?! » :-[
Well, a little introduction about general Fog Color settings is needed. Fog color is used to simulate colorful refractions, the default value is white (glass = neutral). But if we give a color, the glass will result in color: its color will be in relation to the thickness of the object:
  • Thin objects will have light and soft colors
  • Thick objects will have intense and dark colors
Just like the real world.
Here is the effect just for “Fog Color” option:

As you can see, the color intensity changes for thick and thin areas.
Fog Bias! This parameter allows you to adjust the contrast for transition thin-thik areas. If you use negative values you can ​​emphasize the effect producing:
  • darker colors for THICK areas
  • clearer colors for THIN areas
For this reason negative fog bias must be accompanied by a drammatic reduction of the “Fog multiplier” (0.001) to avoid too dark areas.
Here the parameters I used in the first image:
Fog color: 236 – 135 – 5 (rgb) / red color
Fog multiplier: 0,001 / brightens the refraction
Fog Bias: -1.8 / increase contrast thick-thin


Choose a color and balance Multipier FogFog Bias. The reddish color is perfect for “warm glass” , but also with other colors, fun things happen:

( Fog Color = 210 – 238 – 54 / RGB)

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