Furnace glass are glass beads made in a glassblowers glory hole or glass furnace. Furnance glass beads begin as a clear glass melted at the end of a blowpipe. White glass is layered over top and a the hole is created by blowing into the gather of hot glass. Color is added and the large mass of glass is pulled out into a long rod of glass with a center hole. The long rod is cut into bead-sized pieces. A few resources for furnace glass are: Penrose Beads and Mingo and Asho . Mingo and Asho share how they make furnace glass beads on their website.
The Charm Bracelet included in today's post is from Ricky Bernstein's site Penrose Beads