Brief History of Glass
Simple ingredients …
History of ‘Odsidian’ is a natually occuring glass-like substance, produced by the intense heat of volcanoes, it was used by humans for generations, as decoration or split for a sharp edge, but how and when the first man-made glass was produced is a mystery.
There is a theory that suggests mediterranean sailors discovered it accidentally in their fire places upon the beach whilst ashore, they may have mixed together a type of soda with sand and limestone, then noticed a ‘clear’ hard substance among the ashes, if this were the case then the sailors had discovered the same ingredients that are still used for glass manufacture to this very day.
Because of wars and conquests the knowledge of this discovery found its way to Egypt, where the oldest known pieces are dated to about 2000 B.C.. It was the Egyptians who then started the first known ‘glassworks’ dated to about 1400 B.C., and it is believed that Alexander the Great was actually buried in a glass coffin!.
By around 500 A.D. the Roman empire had spread this glass making knowledge throughout the Mediterranean and into British history. In British history in particular the glass making process continued to evolve, and by the 7th century it had already significantly changed.
The ‘crown’ method had been developed, this involved spinning a ‘blob’ of molten glass on the end of a pole to create a flat disk of glass, which was then cut into small pieces. The crown technique developed again by adding a disk to the end of the pole before the glass ‘bubble’ was spun, this still only resulted in the production of small pieces as the quality near the centre of the disk, the ‘Bullseye’, was too bad to use. (ironically the ‘Bullseyes’ are now the most sought after pieces!).
The next development of significance was the ‘cylinder blown’ method, where large ‘bubbles’ of glass were blown and then had the ‘top’ and ‘bottom’ of the bubble cut off to leave a cylinder. This remaining cylinder was then cut down the length, heated until soft, and then opened out by beating it flat on a stone bench using wooden paddles. It is believed cylinders up to 12metres long were cut this way, this process continued until the 19th century with only minimal improvements in production techniques, and the size of the finished glass was still very limited.
1913 was the year that witnessed the next major change in production, when a ‘continuous’ process was developed of drawing up a stream of glass from a vat of molten glass, the edges were held by knurled rollers which controlled the width. The most sucessful of the slightly different forms of this technique was the ‘PPG Pittsburgh process in the U.S.A..
The quality of this glass however was on the whole poor, as the thickness of the glass could not be controlled, this resulted in bad optical quality due to distortion. If glass was needed for shopfronts for example or high-end use it had to be polished down, this was done by casting glass and ‘grinding’ it down using a mixture of sand and iron oxide, as you can imagine this process was VERY messy.
In 1938 this way of making glass was developed into a production line which cast a continuous sheet of glass which was polished on both sides simultaneously, the drawback to this was that the production line itself was huge, measuring hundreds of feet in length, which in turn made the glass expensive. However, this method is still in use today.
‘Float’ glass is now the standard type in use today, and we have Sir Alistair Pilkington to thank for it, he invented the process during the late 1950’s. The technique involves the glass floating on a bed of molten tin, whilst being heated from above.
The finished glass is remarkable in that it needs no further processing before use apart from cutting for distribution!, the glass has an optically good finish and is the type used in 90% of the worlds flat glass. The SK1 float line in Sweden was ‘switched on’ by Pilkingtons in 1976, during a non-stop production run lasting TEN YEARS, it produced an amazing TWO MILLION tonnes of glass. The second non-stop production run (from 1986 to 1999) saw the production of 3.1 MILLION tonnes of float glass!.
Non-stop production lines of glass are now common in many plants around the world, We have come a long way through history, and the creation methods of glass have changed dramatically, yet the ingredients are basically the same as in the bottom of the mediterranean sailors campfires.