Understand the effects of transparency and translucency in your renderings.
When defining a render appearance that uses Generic Material Properties, remember that reflections on a surface are created by light bouncing off it. Of the light that strikes a surface, the Transparency and Translucency properties specify the amount of light that bounces off the surface rather than passing through or being absorbed by it.
Transparency specifies the amount of light that strikes the surface at a 90-degree angle and bounces off. Translucency specifies the amount of light that strikes the surface at a very shallow angle (close to 0 degrees) and bounces off.
To determine the amount of light that bounces off the surface at any other angle, Revit interpolates between these 2 values. The effects of these values can be altered by the value of the Glossiness property.