Fourcault process

At the bottom of the draw is the "pit" or place where the molten glass is sufficiently cooled to be close to forming temperature.

The cooling process uses a device known as a "canal", a box-shaped structure which conveys the glass from the refining area to the pit.

The canal links the pit with the "refining" area, a section of the glass furnace that removes gas bubbles and other sources of imperfection.

The Fourcault process uses a ceramic die to shape fused (or molten) glass into a ribbon of rectangular cross section.

The base of the ribbon is shielded from heat radiation from the fused glass so that it continues to hold the shape imparted to it by the debiteuse.

Sometimes a mild vacuum is applied to the ribbon in this early part of the process since mechanical cooling can induce air currents which impact upon surface quality.

Some manufacturers also will apply sulfur dioxide gas during the draw in order to change the chemistry of the glass on the surface.

Sometimes an expedient measure, using a portable source of heat, can be used to make the checks migrate to the edge of the ribbon where they disappear.

The Float process lets the molten glass settle on top of a pool of liquid tin, so that gravity creates a flat sheet.

Due to various chemistry and physical aspects of window glass the Pilkington Float process produces a vastly superior product.