Making Glass

Glass-making has been part of human history for about 5,000 years. The earliest use of glass probably occurred in ancient Egypt, where glass items were considered luxuries found only in the tombs of priests and royalty. Glass vessels were originally made by covering a clay core with molten glass, then removing the core when the glass cooled. When the blowpipe was invented about 100 B.C., glass-makers could create larger containers in a much shorter time. The new art of glass-blowing spread throughout Europe with the advance of the Roman Empire.

Blow Pipe - 86-2480
Glass maker's blow pipe (blow iron), Canada, gift of Tom King
CMC 986.9.1

After the fall of the Empire, glass-making centres were established in Venice, France, Germany, and Britain. In North America, glass-making was attempted as early as 1608, but the first successful glass works began only in 1739. Glass-making in Canada dates from the 1800s.

Plate - CD94-413-055 Glass plate, Beaded Grape pattern, 1898,
Burlington Glass (also made at Sydenham)
CMC D-4013

The basic recipe of sand, soda, and lime has not changed over the centuries, but many variations exist. For example, adding potash and lead improves the quality of glass, while introducing cobalt, sulphur, or other minerals produces colour. Broken glass, known as cullet, is added to the mixture of raw materials to accelerate the melting process. The ingredients for a batch of glass are mixed and melted in special large pots heated by a furnace.

In the heart of the glass works, the dazzling furnace interior

To blow glass, the glass-blower dips the end of a hollow blowpipe through the "glory-hole" into a pool of molten glass in the furnace. The pipe is rotated until the right amount is gathered as a gob on the end, then withdrawn. By blowing through the pipe, the blower can create a rounded, free-blown bottle. The glass is then attached to the pontil iron and cut from the blowpipe. The object can be shaped by using a tool and wooden paddle. By blowing while the gather of glass is held within a mould, the same shape is achieved each time. After the final shaping, the object is placed in an annealing oven to slowly cool and harden.

Cullet - CD94-453-076 Cullet,
excavated on site of Manitoba Glass Company, Beausejour, Manitoba,
gift of Mac Provick
CMC S-37

With the development of the automatic bottle machine in the early 1900s, the blower's skills were no longer necessary. Commercial glass is now manufactured using bottle-blowing machinery.

The automatic bottle-blowing machine

Flat glass for windows or mirrors was made either by blowing and twirling a glob of glass so that a thin round sheet was produced, or by blowing a long tube or cylinder. The tube was cut at both ends, then slit lengthwise and opened out into a flat sheet while still warm. In modern glass works, flat glass is produced in huge float tanks as a sheet formed over molten tin.

PA-15489 Manufacture of window glass about 1930,
lowering the huge glass cylinders prior to cutting

A recipe for 2,000 pounds of amber-coloured glass
(From the Dominion Glass Company papers, National Archives of Canada)
Sand 1,000 (pounds)
Cullet 500  
Ash 390  
Lime, burnt 100  
Borax 3  
Sulphur 2  
Carbon 1  


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