Silica is the main component of most types of glass, with other materials added for specific characteristics or to lower costs. Soda-lime glass is the most common type, while lead glass is denser and clearer. Other materials can affect glass properties, and clarifying agents are often added to reduce bubbles.
The raw materials for glass vary according to the specific type of glass, but a few are critical to most glassmaking endeavors, and one in particular is found in nearly all types of regular glass. While one material is used as the main component of almost any type of glass, many other materials are added for various reasons such as creating a glass with a particular characteristic or to lower the cost or difficulty of the manufacturing process. Regardless of the type of glass and its components, all materials are reduced to a fine powder before being transformed into glass.
Silica, or silicon dioxide (SiO2) as it is known, is the main component of most types of glass. Pure silica is used to make a type of glass called fused quartz glass because quartz sand is the source of most silica. This type of glass is quite expensive to make as it requires very high temperatures to melt and vitrify the silica. It is mainly used for laboratory and specialty glass containers that require very high temperature tolerance and resistance to expansion or contraction due to temperature changes.
The most common type of glass is called soda lime glass with approximately 90% of the glass produced in the world being of this type. Soda-lime glass uses silica as the major component, but sodium carbonate and oxides of aluminum, magnesium, and calcium are added to the silica with these additives typically making up 25-30% of the glass by weight. These additions lower the temperature at which the mixtures melt and vitrify, becoming glass.
Lead glass is another common type. Using one of the most common raw materials for glass, this type of glass is made by replacing some or all of the oxides used in soda-lime and other common glass types with lead oxide. This results in a dense, very clear glass with better light scattering and reflection that is prized for its quality and is used in fine tableware and objets d’art.
Other raw materials for glass can be added to the silica base and can affect the physical and chemical properties of the glass. These materials tend to be metal oxides such as barium, cerium, iron, and lanthanum, among others. For example, cerium oxide gives glass ultraviolet (UV) absorbing properties. Boron oxide produces a very hard, heat resistant glass like that marketed under the brand name Pyrex. Scrap, which is recycled glass, is also often used as a raw material.
Certain additives called clarifying agents are often added to glass to reduce the size and frequency of bubbles in the glass. For this purpose, common table salt, sodium sulfate and various oxide and hydroxide compounds are used. Some types of specialty glass contain materials such as fluorine and various metal oxides and phosphates, especially those of alkali metals such as calcium, lithium and potassium.
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