Here's a glass bottle with a big chip taken out of it. The image on the left was created using the techniques described in my Refractive Glass tip. It's nice, but there's still something not quite right about it. The glass is uniformly transparent no matter how thick the glass is at a given point.
The image on the right is of the same object, with my Glass Thickener shader script applied to it. Ooh, ahh. Notice how much more detail there is in the refractions, and how the shadows are rendered properly as two shadows, not four.
GThick2 does thickness-attenuated color filtering. It uses a physically-based model, and you can even simulate semi-opaque materials such as apple cider and milk.
