Glass objects can also be made by pressing or drawing. Pressing can be used to make items, like vases, with quite complicated patterns on them. The patterns come from a mould. These can be expensive to make but are stored in the factory to be reused again.
Drawing is the method used to make tubes like fluorescent lights or scientific glassware. Drawing uses a hollow, rotating tool called a mandrel. Molten glass is drawn over the mandrel while air is pumped in at the top. The thickness of the tube depends on the pressure of the air and the speed of the drawing.
In pressing, the gob of glass is dropped into an open mould and the top half of the mould, called the plunger, is pressed down into it. Only dishes and objects which are wide at the top can be made by pressing. It must be possible to get the upper part of the mould in and out. Pressing can be done automatically or by hand.
Glass tubing is made with a tool called mandrel. Glass tubing is made by drawing. The molten glass is shaped over the rotating mandrel with air blowing through it. This forms the tube which keeps its shape as the machine pulls it away from the furnace. The machine is very long — the tractor rollers may be as far as 120 m (400 ft) from the mandrel.
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