Although this tutorial is about making vases, it applies equally well to making tumblers. First create a template by wrapping a stiff material around the glass and trimming it to size. Roofing paper works well for making templates for clay handbuilding. Building it over the original glass helps to hold the structure. Baby power can be used instead of a non-stick liquid to help the clay to slide off. Don't forget to add a bottom.
GlassWood >>> Glass and wood complimenting each other - Hamburg-based design studio Alexa Lixfeld experiments with textures and colours. The collection of handmade and mouth-blown vases was made in Czech Republic - in area famous for the long tradition of glass production. Using the old molds in which the glass is shaped create a unique duos - perfect in their exactness