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Glassmaking
involves two main steps: (1) Heating and
mixing raw materials to produce molten glass, and (2) Forming the
molten glass into the desired shape. Most glass then receives further treatment
to produce the final product. Making Molten Glass Glass manufacture begins with the careful selection and measurement of raw materials. The most important raw material is sand. Other raw materials used depend on the type of glass being made. Broken glass,
called cullet, is usually added to the raw materials. It promotes the melting
of the raw materials as they are heated. Most cullet is waste from glass-forming operations; some is
obtained from recycled glass products. The raw materials and cullet are heated until they have melted into a spongy mass full of bubbles. The temperature of the melt is then increased to make it more fluid, allowing the bubbles to rise to the surface and escape. The glass at this stage is clear and homogeneous. Adding
chemicals into the mix, with particular chemicals creating specific colors,
makes colored glass. We often call these frits and use them in both coloring a
batch or in a fusing technique. Forming When the glass is first withdrawn from the furnace its viscosity is too low for it to hold any form. As it cools, it flows less easily and can be formed. Blowing. In hand blowing, a mass of molten glass
is gathered on the end of a five-foot stainless steel pipe called a blowpipe or
blowing iron. The glassmaker blows through the pipe, giving the material a
hollow, balloon-shaped form. The glass is further shaped with various metal and wooden tools. It is usually reheated several times to keep it pliable while it is being shaped. Pressing. A measured amount of molten glass is
placed into a form, and a metal plunger presses an engraved mold into the glass
blob leaving behind the raised design. Further Processing After forming,
the glass ornament is heat-treated, by annealing, and later may also be
decorated. As glass cools
from forming temperatures to room temperature is shrinks and solidifies. Uneven cooling would weaken the glass
due to stress so we use annealing ovens, known as a Lehr, to control the cooling
process overnight. Glass objects can then be decorated further. Some glass objects are painted or glazed. Others are etched with hydrofluoric acid or soda blasting, either to produce an artistic design or to frost the entire surface. Designs can also be cut or ground into the surface. |