Transmission

Transmission controls how light moves through a material.

Note: If Fresnel is not checked reflection may overpower transmission effects.

If set to color, that color will be the degree of transmission of the material.

If a texture map is selected the mapped image will be used to control the transmission of the material.
Both the color and any texture map rely on classical RGB format coding for the reflection. White (RGB 0, 0, 0) equals total transmission, and Black (RGB 256, 256, 256) equals zero transmission.
Color also affects the color of light transmitted through the material.

Transmission color set to grey, and the Diffusion color is set to white.

Transmission color set to red, and the Diffusion color is set to white.

Transmission color set to grey, and the Diffusion color is set to red

Transmission color set to red, and the Diffusion color is set to red.

As for the reflections, transmission can be glossy or not. Therefore, the same glossiness controlling parameters that are available for reflections are available for transmission.

IOR (Index of Refraction)

What makes the transmission effect acting like a magnifying/minifying glass is the Index of Refraction (IOR) of the material. Users can enter the value they need in the IOR field of choose one in the drop-down list (amongst various real-life material IORs).

IOR set to 1.00

IOR set to 2.00

See how in the previous image, the Total Internal Reflection (TIR) increases with the increasing IOR. In jewelry, where materials have strong IORs, the TIR effect is responsible for most of the final appearance of the object and must be carefully handled.

Example of an applied texture map for transmission

Note: IOR has zero affect when transmission uses a texture map.