The last pieces of GLASS left are textures and materials. All a texture consists of is a name, and a texture file (in RGB format -- save as .rgb in GIMP). Remember openGL requires that textures have edges of length 2^n. e.g. 64x64.
A material consists of the standard openGL material options. Just click on a colour to change. The dialog is:
To apply materials to triangles, this can either be done from the triangle dialog (double-click on a triangle), or when the triangle is created. If the GLASS object you are editing has materials, the combo at the bottom of the vertex toolbox can be set to one of them, meaning the next created triangle will have this material. The material is displayed in the area above the combo box. If it has a texture, this will be shown in the area, making it easy to select texture co-ordinates. An example of this is: