/Understanding Glass
Understanding Glass 2018-05-08T04:43:44+00:00


The transformation of raw materials into glass takes place around 2,400 °F (1,320 °C); the glass emits enough heat to appear almost white hot. The glass is then left to “fine out” (allowing the bubbles to rise out of the mass), and then the working temperature is reduced in the furnace to around 2,000 °F (1,090 °C). At this stage, the glass appears to be a bright orange color. Though most glassblowing is done between 1,600 and 1,900 °F (871 and 1,038 °C), “Soda-lime” glass remains somewhat plastic and workable as low as 1,350 °F (730 °C). Annealing is usually done between 700 and 900 °F (371 and 482 °C).

Glassblowing involves three furnaces. The first, which contains a crucible of molten glass, is simply referred to as “the furnace.” The second is called the “glory hole”, and is used to reheat a piece in between steps of working with it. The final furnace is called the “lehr” or “annealer”, and is used to slowly cool the glass, over a period of a few hours to a few days, depending on the size of the pieces. This keeps the glass from cracking due to thermal stress. Historically, all three furnaces were contained in one, with a set of progressively cooler chambers for each of the three purposes. Many glassblowing studios in Mexico and South America still employ this method.

The major tools involved are the blowpipe (or blow tube), the punty (or pontil), bench, marver, blocks, jacks, paddles, tweezers, paper, and a variety of shears. The tip of the blowpipe is first preheated; then dipped in the molten glass in the furnace. The molten glass is ‘gathered’ on to the blowpipe in much the same way that honey is picked up on a dipper.

Glass created from complex murrine and zanfirico cane can possess a great deal of detail. Glass can be made with precise striped patterns through a process called cane which involves the use of rods of colored glass. This glass is then rolled on the marver (marvering
[16]), which was traditionally a flat slab of marble, but today is more commonly a fairly thick flat sheet of steel. This forms a cool skin on the exterior of the molten glass and shapes it. Then air is blown into the pipe, creating a bubble. Then, one can gather over that bubble to create a larger piece. Blocks are ladle-like tools made from water-soaked fruit wood and are used similarly to the marver to shape and cool a piece in the early steps of creation. The bench is a glassblower’s workstation, and has a place for the glassblower to sit, a place for the handheld tools, and two rails that the pipe or punty rides on while the blower works with the piece. Jacks are a tool shaped somewhat like large tweezers with two blades. Jacks are used for forming shape later in the creation of a piece. Paddles are flat pieces of wood or graphite used for creating flat spots such as a bottom. Tweezers are used to pick out details or to pull on the glass. There are two important types of shears, straight shears and diamond shears. Straight shears are essentially bulky scissors, used for making linear cuts. Diamond shears have blades that form a diamond shape when partially open. These are used for cutting off masses of glass. Once a piece has been blown to its approximate final size, the bottom is finalized. Then, the molten glass is attached to a stainless steel or iron rod called a punty (or a punty rod, a pontil, or a mandrel) for shaping and transferring the hollow piece from the blowpipe to provide an opening and/or to finalize the top. There are many ways to apply patterns and color to blown glass, including rolling molten glass in powdered color or larger pieces of colored glass called frit. Complex patterns with great detail can be created through the use of cane (rods of colored glass) and murrine (rods cut in cross-sections to reveal patterns). These pieces of color can be arranged in a pattern and ‘picked up’ by rolling a bubble of molten glass over them. One of the most exacting and complicated caneworking techniques is ‘reticello’, which involves creating two bubbles from cane, each twisted in a different direction and then combining them and blowing out the final form.

A lampworker, usually operating on a much smaller scale, historically used alcohol lamps and breath or bellows-driven air to create a hot flame at a workbench to manipulate preformed glass rods and tubes.The modern lampworker uses a flame of oxygen and propane or natural gas. The modern torch permits working both the soft glass from the furnace .

Come visit our Local Studio for a Live Glass Blowing Demonstration!

Toggle Sliding Bar Area