Have you ever wondered about how glass can be bent to create windows, such as those often found on corner turrets? If so, then read on.
The process begins with making a template. The radius of the bend is duplicated by creating a glass template. Then the arch of the template is used to fashion the mold for the window. Sheets of steel are cut with the exact bend required and these will form the backbone of the steel cradle onto which the glass will melt and take the form.
Long steel laths are laid across the arched radius of the template, which are then heated before the sheet of custom cut glass is laid across it. Before the glass reaches this point it is cleaned thoroughly and is inspected with an ultra violet light to be certain that the glass is free from any contaminant that might cause an imperfection during the firing process.
In order to prevent the glass from sticking to the mold, it receives a thin coating of detergent, calcium carbonate, and clay. The steel mold is heated for an hour before the glass pane is laid across it and then it goes into the 900 degree gas-fired furnace. But, that temperature is not hot enough to actually make the glass bend.
The glass will sit in the furnace for three hours before the silica molecules become excited enough to bend. At 1300 degrees, the glass bends into the shape of the template. The cooling process also takes place in the furnace, with numerous adjustments in heat and air flow being made in order to ensure that the glass contracts evenly. Slowly, the heat is decreased in different areas of the furnace. This process is called annealing.
Six hours later, a custom bent pane of glass is ready for application, such as for an arched top bent glass window. It is a slow process, but one that cannot be replicated in any other manner. Perhaps knowing that it takes one full working day to fabricate a rounded window for a corner turret window will inspire a bit more appreciation for all of the work that goes into its creation.