1. Preliminaries

As well as anything related to raytracing with Blender, because of the supplementary calculus time required by your computer, raytracing is only an option that you should feel free to activate and deactivate. This is done by the mean of the Render menu. The Shading panel shows an option labeled Ray Tracing you will have to activate in order to use raytracing in your pictures. If you do so, you can deactivate the Environment Map option, even if this one shouldn't bother you if you don't.

2. The Mirror panel

In the Material menu, after having added a new material to any object, you will get all the material properties available. The Mirror panel is folded by default. Unfold it, and then check the Mirror option in order to activate raytraced reflections for your object. From now on, its surface will reflect its environment at rendering time; the other buttons and sliders are here to help you controling this reflectiveness.

2.1 Reflectivity

By default, this value is set to 0.00, which is no reflection at all. By increasing this value up to the maximum (1.00), your object will have the same reflectivity as a perfectly polished mirror. Please note that the reflected colors are strictly those of the original environment, whatever is the base color of your object.

Hints: Colored reflections

Just under the Reflectivity slider, you have a color picker that enables the color of the mirror, that will be tainting the colors of the reflected environment. By default, this color is pure white, which is quite perfect for chrome effects. You can use a yellowish color for golds, an orange one for coppers, etc.

The result is rather obvious:

In most cases, you will find very convenient to have the same Diffuse color and the same Mirror color, but as Blender is more orientated toward artistic freedom than realism, you can set the colors the way you really want. Though, if you want the exact same colors, you can hover the mouse cursor on the Diffuse color picker (for example), just issue a CTRL+C on the keyboard in order to copy it, and then move the cursor over the Mirror color picker and CTRL+V to paste the copied color.

2.2 Depth

In our reality, reflecting objects located near each other will reflect themselves up to infinity, and it is possible to spot in the reflects of one, the reflects of the others. Unfortunately, this behavior will require an infinite time of calculus to reproduce. Most of the time, you only need a recursivity level of two or three to get visually attractive results; because of this, the default value is set to 2. Beware: if you foolishly increase the value of this parameter, you will suffer from from drastically longer rendering time if you have many reflective objects in your scene.

2.3 Fresnel

Let's undertake a small experimentation in order to understand this parameter. After a rainy day, go out and stand over a puddle of water. You can see the ground under the puddle. Now, please kneel just in front of the puddle, your face close to the ground, and look again at the puddle of water. The liquid surface part which is closer to you lets you see the ground, but if you move your glance toward the other end of the puddle, then the ground is gradually masked until all you see is the reflection of the sky. This is the Fresnel effect, and this option sets how much of the surface is effected by it; with a 0.0 value, the surface is 100% reflective, even if the casual observer is glancing from above, and with a 1.0 value, it shows only the natural shader of the object.

2.4 Blend

This option sets the blending factor for the Fresnel effect.

Fresnel effect example

The animated picture below shows a glossy ground on which we will apply the Fresnel Parameters: Fresnel 2.50 and Fac 1.35. It shows quite well the Fresnel effect: when the angle of view of the camera is close to the angle of the horizontal plane, then we can only barely spot the patters on its surface and on the counterpart, we see easily the reflection of the sky on its surface. But when the camera is at the apex of the plane, it's mainly its texture that can be seen.

Fresnel effect demonstration - pay attention to the ground reflections

3. Blurred reflections

A careful observation of the objects in our environment shows that glossy objects (reflective, varnished, metallic, etc.) don't reflect the light perfectly, because of some roughness of their surface, for example. The reflections then look more or less blurred. This is the very purpose of the Gloss parameter: with an Amount value of 1.000, the surface is perfectly reflective ; the lower this value, the blurrer the reflections become. Click on the following pictures in order to witness by yourself how the reflections on the ground loose their sharpness when the Gloss Amount value decreases.

From upper left to bottom right: Amount values of Gloss: 1.000, 0.900, 0.800 and 0.700

The Samples value sets the quality of the blur: high values will provide a very smooth blur but higher rendering times. Threshold is the threshold that puts the sampling to a halt if the previous sample doesn't contribute to the pixel at least at this value (as a percentage), even if the iteration has not reached the set Samples value. Anisotropic allows for anisotropic blur to occur (when the value equals 1.000) enlighting the direction of the surface's tangent ; with a null value, the blur is perfectly circular. Anisotropy is especially useful for machined objects (lathed objects, for example).

Max Dist sets the maximum distance a ray will travel in order to find a pixel to reflect ; once this distance is reached, the pixel from which the ray has been emitted will herit one of the two following colors (as set by the Fade-out color drop menu):

  • Fade to: Sky: the pixel herits from the color of the sky, as set in the World menu
  • Fade to: Material: the pixel herits the base color of the material

This last option is very interesting for varnished objects that are reflective only over a short distance.

Article written on December the 26th, 2004.
Updated on November the 17th, 2008 for Blender 2.48a. Comments re-initialized.
Updated on June the 13rd, 2010 for Blender 2.50 Alpha 2.