Thanks for your reply, Hoofdcommissaris. However, Im not referring to the Fresnel effect -- but I probably didnt word my question well.

What I would like to know is how to build an object shader that makes the object less transparent in direct proportion to how thick the object is. A thin piece of coloured glass will transmit more light than a thick one. Similarly, if one excludes Fresnel and refraction effects, a sphere of coloured glass will be more transparent near its edges than near its centre, where the glass is thickest.

Can you, or anyone else, help me out with this?