According to Roman glass expert E. Marianne Stern, the discovery that glass can be inflated by blowing was made around 90 B.C., and the first blowpipes were probably made of clay. Today, glassblowing is used to make a wide range of decorative and functional objects, such as bowls, vases, amorphic vessels, glass fruit, votive candle holders and sculpture.
Gathering and Centering
To blow glass, you first need to dip the end of your pipe, or blowing iron, into the furnace to gather a globule of molten glass. The globule is often referred to as a "gather," and because of its consistency, it has a tendency to want to slide off the end of the pipe. To stop this, you need to use a technique where you keep the pipe continuously rotating. Use gravity and work with the flow of the glass to center it. You can also roll the blowpipe on the arms of the glassblower's bench, a kind of work station, to keep the gather centered.
In free blowing, you produce the form you want by blowing short puffs of air down the pipe. Blow gently but firmly and the molten glass will start to inflate, or expand. When the temperature of the molten glass has fallen so that blowing is not as effective, you need to place the work in a glory hole. This is a gas-powered refractory chamber, or barrel-shaped furnace, in which you reheat the glass so that you can continue blowing it. The other blowing technique is called mold blowing. For this, you inflate the gather into a preformed mold of metal or wood, so that it takes on the shape and size of the carved out space. You need to control your blowing so that the molten glass reaches every part of the mold interior.
You can roll your work on a polished steel slab called a marver to shape and cool it. If you sprinkle color chips or powder on the marver when you roll your gather on it, the molten glass will collect the chips or powder, giving your work color and design. You can also add color by using solid color bars. You break these up into chunks, heat them in a small kiln, melt them in the glory hole, gather the molten glass on your work and either free blow or mold blow it.