VRay for SketchUp Manual

Open file: Chairs-Refraction-Original.skp. We are going to introduce how to add and edit the refraction layer. Select the red chair from above. Select "Materials Editor" icon over V-Ray toolbar to edit chair material.

Add Refraction Layer

1. Click on the "+" to the right of the Chair_Red, and then right click on Refraction Layers. Select Add new layer. You will see the Refraction layer added to the right of the window.

Controlling the amount of transparency

2. If you don't see the transparency from the material preview window, that's because the Transparency is set to black. Use this color to adjust the degree of Transparency. Click on the color and change it to white, which will give you 100% of transparency to the material.

3. Click on the Update Preview again and you will see the transparency, but without its original red color. When you set the transparency to 100% white, no matter what you have for diffuse color, it will not show up. It will render like the image at the bottom.

The color of refractive materials

When you want to apply color to a refractive material, the best way to do this is through the Fog Color, which is located to the lower right of the Refraction dialog box.

4. Click on Fog Color and change it to the same color as the original Diffuse Color. Click on the Update Preview and you will see the red color show up on the material this time.

Image on the left is what you will get. Do the same changes to the other two colors and you will get the image looks like the one to the right. Under Render Environment, change the background color from black to white and see what you will get this time.

Fog Settings Explained

The appearance of Fog depends on three parameters; Fog color, Fog Multiplier, and object size. The Fog color is a very important factor, and the wrong color can make it hard to achieve your desired effect. It is best to set your color to a very light or desaturated version of the desired color. The Fog multiplier will be determined by the Fog color and the object size. The object’s size is important because Fog is created by calculating how much light penetrates an object. Therefore, a larger object will absorb more light than a smaller object. This means that a single setting will not necessarily produce the same effect from object to object. The image below is two spheres with the same material applied to them, but the sphere on the right is 4 times larger. The following images below are tests of different multipliers with a saturated and desaturated color.

Fresnel IOR: 1.55
Refract IOR: 1.55
IOR: 1.55
Fog Color: R244, G250, B230

Fresnel IOR - 1.55
Refract IOR - 1.55
IOR - 1.55
Fog Color - R175, G250, B0

Adjusting Refractions with Index of Refraction

IOR (Index of Refraction) is used to calculate among of the light refracted from a transparent object. The newly added IOR default is set to 1.55. Please see the chart for typical objects' IOR value.

Default set the Refraction IOR to 1.55; please refer to the images below for setting the IOR to create your desired material.

Please note that reflection and refraction IOR values are separate, but to achieve an accurate effect these values should be the same.

The Glossiness of Refractive materials

Both refractive objects and reflective objects have an option setting for Glossiness. The difference is that Reflection Glossiness only affects the surface, whereas Refraction Glossiness will have an effect on the object’s transparency.

The Glossiness of a refractive object is usually used to represent different type of glass, for example, frosted glass. The refractions will become more blurry as the value is decreased, and at a certain point these refractions will become so blurry that they prevent what is behind the object from being distinguished.

Refraction Glossiness default is set to 1.00, please refer to images below for impacts on different settings of Refraction Glossiness.

Images below set the Refraction IOR to 1.55, you can see the Glossiness changes gradually from 0.85. It changes rapidly between 0.80 and 0.75. When the setting for Refraction Glossiness remains the same, different Refraction IOR will change the Glossiness of the object.

Just like the intensity of the Fog Multiplier affects its transparency, the Refraction Glossiness in thicker objects becomes more obvious.

Image below shows the influence of Refraction Glossiness material to objects behind it. Objects further away become very blurry.

Shadows of refractive materials

There is an Affect Shadow option to the right hand bottom corner of the Refraction dialog box, default is unchecked. When checked, the color of the transparent object will affect its shadow and it's not black anymore. The shadow also becomes more depth as well.

It is recommended to always have Affect Shadows checked, as it produces a more realistic effect.

Images below show the difference with and without the Affect Shadows checked.

Double-sided material

Under Options of each material, you will find this Double-sided selection. Default setting is checked. This option is particularly important for transparent material. When this option is unchecked, light that enters the inside surfaces will not be rendered and show up black. The reason to have this option is that sometimes you may want to uncheck this option when render object with translucent material in order to get the right texture.

Unless you want to create some special effects, please have this option checked.

The double sided option will not have any affect on the shadows of the object.

Translucent material

We've talked about changing the Diffuse color to get the degree of transparency we want to create before. White means 100% transparent, black means 100% opaque. You can create translucent materials with colors anywhere between white and black. But now we want to introduce a different translucent material. It is related to special light absorption materials.

Open file: Translucency.skp and render it, you will get image like below. You will see that colors where partitions meet the outside box and at the base of the box are darker. This is because the thickness of the object changes and the light travel distance changes also. So the degree of light absorption varies. To create this kind of material, you have to check the Translucency option under the Refraction.

Check the Translucent box under Translucency first. Thickness is for control of light pass through the object, the unit for this is unclear. Keep these three settings as default. Other items required to change include:

1. Double-Sided must be unchecked so the light can get through to the inside of the object. This setting is extremely important.

2. Change the IOR to 1.

3. Decrease the Refraction Glossiness to a value below 1.

4. Do not use white color for the Transparency because that will turn the object to completely transparent and become dark after rendered due to absorb too much light. Do not use black color, either. That will not allow light get through the object at all. Pick a color anywhere between Val 80~150 will give you the best result.

Many rendering engines use Sub-Surface Scattering (SSS) to create this kind of material. This material is good for creating things like: wax, skin, milk, cheese, plastic and jade which all have a little translucency in it.

Translucency is created by absorbing light to the object's surface so the color of the object will show up a little darker than its original color. If you still think that it's too dark even though the original color is set to the highest Val 255, the best way to fix it is increasing the intensity of your light in the scene.

Below are some examples.