What is a Glass Furnace?
A glass furnace is a large, oven-like structure made for the sole purpose of melting glass in large quantities. Such furnaces are typically kept by artists and workshops that use clear and colored glass as their work media. There are two types of glass furnaces, a pot shaped and an oven shaped furnace. Oven shapes are typically more dangerous to make and use because they are larger, use multiple burners, and generate significantly more heat. A minor fault in their construction can be catastrophic. Pot furnaces are not difficult to make, and are much safer.
Most pot glass furnaces are made from a 55 gallon steel drum. Vermiculite, castable refractory and water glass are all made use of in large quantities for heat-proofing the drum. Thick plywood and sheet metal are also instrumental in making a pot furnace. A saber saw, welding torch and power drill are all used to construct a glass furnace. Most pot furnaces use natural gas as the heat source because it is more fuel efficient. For that reason, a burner and gas regulator will need to be obtained from the gas company. Minor accoutrements include sheet metal screws and heat resistant paint.
Begin by cutting the 55 gallon drum in half so that the bottom half forms the base of the pot. Cover the interior and exterior with the heat resistant paint. Mix up the vermiculite in equal proportions with the water glass to form a sticky, glue-like granulated substance. Lay it down about 3 inches thick into the base, letting it harden before continuing. Mix up the castable refractory, which is a heat resistant, cement-like material, and pour an inch of it into the base. Once this is dried, drill a hole into the side of the drum, roughly level with the top of the castable refractory. This will function as the drain once the glass melts. Some people prefer to leave the drain open at all times, others prefer to fashion a removable plug from vermiculite and water glass. Measure 3 inches down from the top of the drum, and place the sheet metal screws in a ring pointing inward. Cut the sheet metal and plywood in circles one inch less than the circumference of the drum, and coat them both with heat resistant paint. Place the sheet metal circle into the drum so it sits on the screws. Pack more vermiculite and water glass in a layer atop the sheet metal, forming a tight plug. Remove the sheet metal with its drying vermiculite, and place the plywood cover on top. This part will act as a cover for the furnace melting chamber. Drill another hole in the side of the drum, and weld into place the burner. The regulator valve should be behind the burner, which attaches to the natural gas source.