In this series of Turbo Tips, we’re giving you an in-depth guide to regular V-Ray Material. We’ll cover the theory behind many of the features of the material and give you specific examples of settings and tricks to use. While the example images are from 3ds Max, the same concepts and settings can be used in V-Ray for Maya. The information covered here is generally useful in V-Ray for C4D, but the specific fields and values may be different.
Last week, we talked about the Reflection tab. This week, we’ll be moving on to:
Refraction
Refraction controls how an object lets light through. For example, if you were to shine a light on an object, how much light would you see coming through the other side? Unlike Reflection, not all objects are refractive. Some typical examples that use this V-Ray material component are: glass, water, transparent plastic, crystal, oil, etc.
The amount of Refraction can be controlled by a number, Map, or Texture. It can be grayscale or colored, but it is recommended to stick to grayscale for more realistic results.
If you are not using Caustics in your scene (most likely you aren’t), turn on the “Affect Shadows” option to get realistic, transparent shadows. Otherwise, the shadows will be too dark.
Adding Color To Refraction
So, how do we actually get colored refractions, if it’s not recommended to use colors in the Refraction amount? We should use the Fog color option, in this case. It works realistically, since thicker parts of the model will be more colored/darker than the thin parts.
Depending on your object’s physical size, you might need to adjust the Fog Multiplier Value. Larger objects will look darker than smaller ones when using the same material.
Use Fog Bias to control the color transitions. Lower values make the color more intense and the transitions sharper, while higher values make the tinting more weak but even. If you adjust both of these parameters (Fog Multiplier and Fog Bias), you should be able to achieve any effect you might need.
Refraction Glossiness
Refraction Glossiness simulates a rougher surface, by diffusing the light rays in different directions. Lower values create a rougher look (frosted or sand-blasted glass, or textured rough plastic), and higher values are for smooth surfaces. Since glossy Refractions are one of the biggest increases for render times, they are usually used in a smaller range. You probably don’t need to go lower than 0.7 to achieve the desired look.
You can use a Texture to create a rougher, more realistic look. If the material is still pretty clean, don’t overdo it and use a map that is mostly pure white with some darker spots/patches. It’s usually a good idea to keep the Refraction Glossiness map similar to the reflection glossiness. Any rougher areas would affect the Reflections and Refractions in a similar way.
Note: As with Reflections, we think it’s best to leave the Subdivs at 8, for the end user (your customer) to adjust for themselves.
Refraction Depth and Exit Color
The Refraction Depth and Exit Color function exactly the same as their Reflection counterparts: bump up the max depth if there are lots of refractive/reflective objects and bring it down if using blurry Refractions.
Refraction IOR
IOR is a very important parameter to set correctly, in order for your material to look believable. Fortunately, these values have been calculated for all sorts of materials, so there’s no need to guess here.
With the Value of 1 (same as air), the rays of light are going straight through the object without any distortion. As you raise the number higher, the rays get distorted more and more.
Acetone 1.36
Agate 1.544
Air 1.0002926
Alcohol 1.329
Amber 1.546
Amethyst 1.544
Crystal 2.00
Diamond 2.417
Emerald 1.576
Ethanol 1.36
Glass 1.51714
Glass, Albite 1.4890
Glass, Crown 1.520
Glass, Crown, Zinc 1.517
Glass, Flint, Dense 1.66
Glass, Flint, Heaviest 1.89
Glass, Flint, Heavy 1.65548
Glass, Flint, Lanthanum 1.80
Glass, Flint, Light 1.58038
Glass, Flint, Medium 1.62725
Ice 1.309
Jade, Nephrite 1.610
Jadeite 1.665
Methanol 1.329
Moonstone, Albite 1.535
Nylon 1.53
Onyx 1.486
Opal 1.450
Plastic 1.460
Plexiglas 1.50
Polystyrene 1.55
Quartz 1.544
Quartz, Fused 1.45843
Rock Salt 1.544
Ruby 1.760
Sapphire 1.760
Tiger eye 1.544
Topaz 1.620
Tourmaline 1.624
Turpentine 1.472
Turquoise 1.610
Water 35’C (Room temp) 1.33
Zirconia, Cubic 2.170
Breaking the Rules
Technically, both the Reflection and Refraction IOR should be the same, but sometimes, you might want to unlock them for artistic reasons. This trick is used when glass or transparent plastic material just seems to lack reflections. In this case, bumping up the Reflection IOR can help in bringing out those reflections. It’s also useful when you want to create a more even distribution of the reflections, without increasing their intensity.
Dispersion
Dispersion controls how the light is split up into different colors when passing through an object. A classic example of this would be a ray of light going through a prism, creating a rainbow effect. Most glass and other refractive materials show at least a little bit of dispersion. The exact amount is controlled by the Abbe number. The basic idea is, as the Abbe number goes lower, the dispersion effect increases. It’s easy to overdo it, but it should actually be pretty subtle.
Since it is quite slow to render, most of the time you can get by without dispersion. We only suggest using it for close-up studio renders of things like jewellery, glass, or crystals.
Refraction & Alpha Channels
Finally, a quick tip to remember: for Refractive objects, it is generally a good idea to set the “Affect Channels” to “All Channels.” This way, your alpha channel will not be solid white, but will be adjusted, depending on the transparency of the object. This is very useful in post-production.
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Next week: V-Ray Material, Part 4: Bump
This series of tutorials was made with our friends at Viscorbel.
If there are any topics you’d like to see in a future edition of TurboTips, let us know in the comments below, or Tweet your question to @TurboSquid with hashtag #TurboTips.