Foundations of Construction: Manufacturing a window from a glass cylinder      

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By Susanna McLeod

Special to Ontario Construction News

Crystal clear, smooth, and with strength and energy efficiency built in, modern architectural glass is the eye-catching gem in the contractor’s toolbox. Excellent quality is standard, but in early Ontario, flawless glassmaking was only a dream. Builders were lucky if the window glass was smooth, let alone clear.

Nearly all window glass was imported from the United States or Europe into Upper Canada. Entrepreneurs saw opportunities but making the special glass locally was not economically feasible without stiff tariffs. Several plants opened in Ontario only to close shortly thereafter. In 1881, one eastern Ontario firm managed to achieve intermittent production for two years.

Before opening Napanee Glass Works, John Herring invested two years into visiting several American window glass factories to learn about the industry. Purchasing land close to the Grand Trunk Railway for easy shipping, Herring began construction in June 1881 and completed 10 buildings to house the works five months later.

A furnace for glassmaking was constructed to withstand high heat for extended periods of time. “Furnaces are mainly built of blocks of fire-clay which have received definite forms whilst in a plastic [malleable] condition,” writes Harry J. Powell and Henry Change in The Principles of Glass-Making (G. Bell and Sons, London 1883). “These blocks before being used are allowed to become completely dry, but are not burnt.”

Purchasing state-of-the-art tools, Herring hired experienced European and American glassmakers to operate the equipment. “The furnace comprised ten pots for the melting of the glass, and the daily output was expected to be 80 full boxes, each containing 100 sq. ft. [9.29 sq. m.] of glass,” quoted Antony Pacey in “A History of Window Glass Manufacture in Canada” in 1981. Average annual costs “for wages and supplies was projected to be between $40,000 and $50,000.”

However, struggling with labour union strife and competition from imports from the start, Napanee Glass Works closed after only two years. Herring absorbed a painful loss of about $65,000, said James A. Eadie in Dictionary of Canadian Biography, Vol. 12, 1990.

In the 19th century, flat pieces of glass were mechanically difficult. Enormous cylinders of glass were hand-blown by skilled workers, the pieces as massive as 4m length by 66m circumference, and 1.77m by 1.52m. “After the cylinders cooled, the two ends were cut off and the cylinder split longitudinally,” wrote Pacey “The split cylinder was reheated then handed over to the’flattner.’”

A six-stone coal-fired oven was used “for flattening cut glass cylinders,” according to Eadie. An annealing furnace installed at the Glass Works was the first such remarkable apparatus in Canada. Differing from the traditional kiln, the annealing furnace was “a revolutionary system of lehrs, tunnel-like structures through which the glass sheets were drawn to cool.”

When finished, the glass was rarely close to transparent. As they worked on the sheet, “the founder, skimmer, gatherer, and blower have all stamped their brand upon it,” remarked Powell and Change. Bubbles were elongated by stretching the cylinder, and the surface was dappled with glass threads, speckles, and scratches, and bent from the annealing oven heat. The blower operator had problems with steadiness and the material’s thickness varied from thin to heavy.  “All, however, are not bad,” added Powell and Change, “but, the good are generally in the minority.”

More economical furnaces were developed before the end of the 1800s, Pacey mentioned, and an efficient lehr “was introduced enabling glass sheets to be cooled and annealed in 30 minutes as opposed to the previous seven or eight hours.”

By the next century, advancements made window glassmaking less labour intensive. American inventor John Lubbers invented a mechanical blower, ready for commercial production in 1905. “Using the tank furnace, a ring or ‘bait’ was rested on the surface of the molten glass and then pulled upward in a cylinder produced by pumping compressed air,” stated Pacey. The mechanical system produced glass cylinders up to 12m long with a .76m circumference. The machine “produced better, cheaper and larger sheets of window glass.”

The float glass process was developed over seven long years by Sir Alistair Pilkington in Britain. and ready for production in the early 1960s. “Molten glass, at approximately 1,000ºC, is poured continuously from a furnace onto a shallow bath of molten tin. It floats on the tin, spreads out and forms a level surface,” said “Pilkington: The Float Process,” NSG Group. “Thickness is controlled by the speed at which solidifying glass ribbon is drawn off from the bath.”

The material blend has changed little over the decades, using sand or silica with little impurity, sulphate of soda, and powdered and sifted limestone. Still used in today’s glassmaking, the molten tin container in Pilkington’s float glass process may be up to 50 metres in length.

Modern windows have a common denominator with predecessors. Even the best glass can break.

© 2020 Susanna McLeod. McLeod is a Kingston-based freelance writer who specializes in Canadian history

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