The Ultra Render engine is capable of producing more realistic transparent or translucent materials. When ultra render is running you can access extra shaders to achieve this effect.
To access ultra shaders, select the object you are editing, open the material panel > select Advanced Options.
Index of refraction
Refraction refers to the distortion or bedding of light that occurs when it passes through a translucent object. A good example of refraction is when something is viewed through a glass of water. Items in or behind the glass appear distorted.
Refraction occurs due to light slowing down as it travels through different mediums. The index of refraction refers to this reduction in speed, and is represented by a number. The higher the refractive index, the slower light travels - for example, the refraction index of plate glass is 1.52 meaning the light travels 1.52 times slower through glass than through a vacuum.
You can look up refractive indexes for different materials easily online. Edit this setting using the slider, or typing in a value.
Transmission is the amount of light that passes through a material. This determines how transparent or opaque the material appears.
Unlike the opacity setting, the transmission setting does not remove the appearance of any textures.
This colour is used to tint transparent materials, like coloured glass. This changes the colour of the light as it is transmitted through the material (unlike the diffuse base colour or colour overlay, which are only applied to material surfaces).
The extent to which light stops at a surface and does not reflect or refract. Surfaces with high absorption appear dark and opaque. Wood is an example of a material that totally absorbs light.
This setting controls the way light is dispersed as it passes through a material to produce a prismatic effect. This is desirable when rendering things like gemstones. Dispersion is diisabled when set to 0.
Anisotropic material settings give you advanced control over the way highlights appear on a material surface. This material type is most commonly used for simulating brushed metal textures.
Sheen refers to light that appears to be reflecting from within or behind a textured surface. This is commonly used to simulate textures like velvet or peach fuzz.