3: Glass Melting

Production of glasses by melting involves four steps: batching, batch melting, fining, and homogenization. Batching involves the selection of raw materials, calculation of the concentrations of each material, weighing, and mixing of powders, and occasionally, liquids. Batch melting involves the decomposition of the raw materials to form the initial melt, and control of temperature and atmosphere during the time of formation of the liquid. Specialized techniques are often required for production of glasses from non-oxide and/or toxic materials. Fining, or removal of bubbles, occurs by either bubble rise or bubble absorption. Bubble rise is assisted by formation of large bubbles during batch decomposition, by low melt viscosity, and by use of proper particle sizes for batch components. Special chemicals known as fining agents are often added to batches to promote fining. Finally, production of a homogeneous glass requires the elimination of the heterogeneities inherent in producing a melt from a large number of components with widely different properties.