The molten glass flows from the melting pot into the lower portion of a form. The top piece of the form is then lowered, molding the glass into its shape. After the glass has been formed, it is referred to as green glass, but the glass is reall y transparent and amber in color.

After the glass has been formed, it is allowed to cool slowly, so as to avoid a lot of internal stress in the glass. When the glass has cooled to room temperature, it is inspected based upon some strict guidelines. This is so that the best poss ible product can be passed along to the customer.

In this final stage, the green glass molds are reheated to change the glass into a ceramic. This is done by changing the internal structure of the glass from random to crystalline. The material is heated and held at a temperature around 760° C or higher for over 20 hours. The formation of crystals in the material depends upon the rate of their growth and the number of nuclei that are formed. The glass cannot form its own nucl ei, so metal oxides are added as nucleating agents to the glass during the mixing process. By separating the nucleation and the crystallization process it allows the heat that builds up within the ceramic to dissipate without causing any undue stress to t he material.

For Corning Wareä , the molds are heated at a constant temperature for around 30 hours. After this amount of time, the amount of crystalline structure is roughly the same as the thermal expansion coefficient and is 98-99% crystalline. An example of the relationship between the thermal expansion coefficient and heating time is shown below.