In its molten state, glass can be shaped by casting, blowing, pressing, drawing or rolling.

Casting

In casting, known since ancient times, molten glass is simply poured into a mould and allowed to cool and solidify.

Blowing

The revolutionary discovery that glass could be blown and expanded to any shape was made in the third quarter of the 1st century BC in the Middle East along the Phoenician coast. It was found that molten glass on the end of a hollow pipe could be inflated like a bubble. In blowing glass a gob of molten glass is gathered on the end of a blowpipe, through which air is blown to form the glass into a hollow sphere or parison. The size, shape, and wall thickness of the glass are controlled by the pressure of the air, the angle at which the pipe is held, and the speed at which the glass cools. The glass is formed into different shapes by the glassblower with simple tools as the pipe is twirled on a special bench. For 2,000 years it was the standard method of glass production and even today, hand blowing is still used in the making of fine decorative glassware…

Pressing

The process of press molding is relatively simple. Molten glass is poured into a patterned mould and forced into shape by the pressure of a plunger. Throughout the 19th century the process was refined and hundreds of patents were taken out for improvements to the technology. Multi-hinged moulds enabled containers of considerable height to be produced. Air pumps gave greater pressure than manual presses and made possible sharper detail, which rivaled cut glass. Moulds continued to improve as special cast iron with a very fine grain became available. Precision lathes and power-assisted routing tools enabled complex shapes to be made and hand finishing was eliminated as moulds incorporating handles were produced.

The relative cheapness of pressed glass and the changing social habits of the Victorians caused an explosion of glassware to be produced at the factories. Bowls and dishes for every possible use began to flood the market. Tableware, fancy goods and glass novelties were affordable by everyone. Penny goods were common from the 1880’s through to 1914.

Molded glassware with an iridescent finish became popular at the end of the 19th century. Shimmering rainbow colours were formed by fixing vapours of metallic compounds onto the glass. Tiffany made iridescent glass fashionable with exquisitely designed pieces in fluid art nouveau shapes. The style was soon copied by the factories who produced the ware at much lower prices. It was made in many different countries but top quality "Carnival " glass was made in America between 1908 and 1928.

Drawing

Molten glass can be drawn directly from the furnace to make tubing, sheets, fibres, and rods of glass that must have a uniform cross section. Tubing is made by drawing out a cylindrical mass of semi fluid glass while a jet of air is blown down the center of the cylinder.

Rolling

Sheet glass, and plate glass in particular, was originally produced by pouring molten glass on a flat surface and, with a roller, smoothing it out prior to polishing both its surfaces. Later it came to be made by continuous rolling between double rollers.

Today the rolling process makes patterned, figured and cast glass products, whereby the semi-molten glass is squeezed between metal rollers to produce a ribbon with controlled thickness and surface pattern (produced by designs incised in the rolls). Wire glass, made by introducing wire mesh into the molten glass before it passes between the rollers, resists shattering when struck. Safety glass, for such items as car windscreens, is made by sandwiching a sheet of transparent polyvinyl butyral plastic between two sheets of thin plate glass. The plastic adheres tightly to the glass and holds the broken shards in place even after hard blows.