My 2 cents. apd001 is correct. Both in shader and glass thickness observation. I use a Cycles shader similar to his/hers with the addition of a Fresnel calculation so I can use it on anything from water to crystal in addition to glass. The Glossy roughness controls how frosted the glass surface is and is the place to add maps for etching and the like. Adjusting the Transparency colour will change the colour of the glass itself so as to make water and other liquids thus the Fresnal.