Forming
The Fourcault Process uses a ceramic die to shape fused (or molten) glass into a ribbon of rectangular cross section. The die, known as a Debiteuse, floats in the molten glass inside of the pit to a prescribed depth which slightly pushes a part of the molten glass slightly above the top surface of the die. A slot is cut through the center of the Debi. which is shaped to produce the best quality of glass.
The Debiteuse is the starting point of the vertical draw, where the glass begins to change from a hot syrupy mass into useful flat glass. We will call the glass from the point of the Debiteuse until it is cut a "ribbon".
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. This cooling preserves the rectangular cross section of the drawn glass by cooling the ribbon glass below the temperature where it would collapse into a column or break back into the melted glass. It is especially important to shield the outside edges of the ribbon from heat so that they are firmer and will hold the rest of the ribbon in a proper shape. In some cases manufacturers will allow the edges to form thicker "bulbs", which are removed after final cutting.
Immediately after being drawn the ribbon is cooled using mechanical coolers so that it maintains its rectangular shape in two dimensions, but assumes a ribbon like structure that extends down into the Debi and upwards into a drawing assembly. This mechanical cooling allows the ribbon to hold its integrity. In the author's experience the mechanical coolers used water, contained in specially shaped radiators, to remove heat radiated by the ribbon.
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.
Read more about this topic: Fourcault Process
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