The English language is filled with glass references: people in glass houses shouldn’t throw stones; a particularly vulnerable fighter has a glass jaw; a dazed person is glassy eyed; a cogent point of view is clear as glass.
Maybe humanity’s interest in glass originates in finding and using obsidian – a common, naturally occurring glass formed from volcanic eruptions – but it is generally accepted that glassmaking emerged more than 3000 years ago, in Egypt and Mesopotamia.
Glassmakers developed techniques for casting objects, using earthen moulds, about 1500 BCE, and the craft of glassblowing emerged more than 2000 years ago.
An article about the chemistry of glass, published by the Corning Museum of Glass, run by the US-based glassware giant Corning, says there is no one composition that characterises all glass, but it is basically made from three simple ingredients: sand, soda ash and limestone.
More specifically, it describes “formers”, the largest percentage of the mixture to be melted. In a typical soda-lime-silica glass, the former is silicon dioxide in the form of sand.
Fluxes lower the temperature at which the formers will melt. Sodium carbonate and potassium carbonate, both alkalis, are common fluxes.
Stabilisers make the glass strong and water resistant. Calcium carbonate, often called calcined limestone, is a stabiliser, without which, water and humidity attack and dissolve glass.
Depending on the composition of the glass being made, melting occurs over a range of temperatures, usually 590 to 760 degrees Celsius.
The Encyclopaedia Britannica says that in 1830 French chemist Jean-Baptiste Dumas demonstrated that soda-lime-silica glass was strongest “when the ratio of the three was 1:1:6; this is essentially the modern soda-lime-silica composition”.
Today, our light-filled homes and workplaces, constructed with vast expanses of glass windows, owe much to several competing inventors, but on 25 March 1902, Irving Wightman Colburn patented a machine that made the mass production of glass for windows possible.
Colburn was born in Massachusetts in the US on 16 May 1861.
In 1899 he started developing a way to mechanise the production of sheet glass. As the website Today in Science History explains, by 1906 he had formed the Colburn Machine Glass Company and by 1908 the company had machines operating at two factories.
Colburn’s process began with an iron rod lowered lengthwise into a tank of molten glass. When the rod was slowly raised, some of the thick liquid stuck to the rod, drawing a ribbon of glass horizontally over a set of rollers, which roughly formed a flat sheet of glass as it continued to be drawn out of the molten reservoir.
According to an article published by the University of Toledo, in Ohio, Colburn’s inspiration came to him while eating pancakes with syrup. “He noticed that after cutting the pancakes, the syrup clung along the length of the knife blade as he lifted it. It occurred to him that a sheet of molten glass could be pulled up in a similar manner.”
Although his efforts appeared promising, by 1912 he’d produced only poor-quality glass in limited amounts and was bankrupt. He sold his assets, including his patents, to Edward Libbey, whose Libbey Glass Company, in Toledo, Ohio, was one of the country’s leading glass producers.
Libbey retained Colburn so he could continue developing his process.
Another glassmaking pioneer, Michael Joseph Owens, was born on 1 January 1859 in West Virginia.
A 2013 article in Investor’s Business Daily, by Scott S Smith, describes how Owens joined his father in the coal mines at age nine, but an eye injury led him to become an apprentice glassblower.
By age 15 he was a journeyman glassblower and not long after became a manager at Libbey Glass, Toledo.
In 1891 Libbey opened a plant in Findlay, Ohio, and Owens was put in charge of making the glass bulbs for Edison General Electric’s electric lights.
Owens set about finding ways to simplify the process. First, he came up with a mould-opening device that could be operated by a glassblower by foot. “It was the first major change in glassmaking in 2000 years,” Smith says.
He next developed a paste that would prevent the bulbs from sticking to the moulds.
Smith says these two improvements “lifted productivity nearly 900%” and “lowered the cost of bulbs by 90%”.
With Libbey’s purchase of his patents, Colburn and Owens went to work perfecting Colburn’s process.
By early 1916, they had succeeded, and the Libbey-Owens Sheet Glass Company was formed. A new factory in West Virginia went into operation in October 1917, but Colburn did not live to see his process succeed. He died on 4 September 1917.