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History of Glass

History of Glass Making

FURNACE (LEFT) The transformation of raw materials into glass takes place around 1315°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 1100°C. At this stage, the glass appears to be a bright orange colour. Though most glassblowing is done between 870–1040°C, "Soda-lime" glass remains somewhat plastic and workable as low as 730°C. Annealing is usually done between 430–480°C. Ingrid Pears uses the finest crystal glass to produce her unique designs which remain maleable for some time.

Glassblowing involves three furnaces. The first, which contains a crucible of molten glass, is simply referred to as "the furnace." (LEFT) The second is called the "glory hole" (BELOW RIGHT)

Glory hole (RIGHT) 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. Ingrid Pears uses three separate pieces of equipment.The major tools involved are the blowpipe (or blow tube), the punty (pontil or punt), bench, marver, seers, blocks, jacks, paddles, tweezers, 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.

Then, this glass is rolled on the marver (Marvering) which was traditionally a flat slab of marble, but today is more commonly a fairly thick flat sheet of steel or graphite. 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.  Newspaper (LEFT) can also be used to shape the glass. The glass floats on a bed of steam on the top surface of the newspaper and shapes the glass.

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 like 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 piece is transferred to a punty, and the top is finalised. There are many ways to apply patterns and colour to blown glass, including rolling molten glass in powdered colour or larger pieces of coloured glass called frit. Complex patterns with great detail can be created through the use of cane (rods of coloured glass) and murrine (rods cut in cross-sections to reveal patterns). These pieces of colour 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.