Raw materials for glass vary depending on the specific type of glass, but some are key to a majority of glass making endeavors, and one in particular is found in almost every type of normal glass. While one material is used as the primary component of almost all types 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 glass type and its components, all materials are rendered into a fine powder before being made into glass.
Silica, or silicon dioxide (SiO2) as it is known, is the primary 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 for most silica. This type of glass is rather expensive to make since it requires very high temperatures to melt and vitrify the silica. It is used primarily for laboratory glass and specialty containers that require very high temperature tolerance and resistance to expansion or contraction due to changes in temperature.
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 its main component, but sodium carbonate and oxides of aluminum, magnesium and calcium are added to the silica with these additives typically comprising 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. Utilizing one of the next most common raw materials for glass, this kind 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 improved light dispersion and reflection that is prized for its quality and is used in fine tableware and art objects.
Other raw materials for glass can be added to the base of silica 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. Cerium oxide for example gives glass ultraviolet (UV) absorption properties. Boron oxide makes very hard, heat-resistant glass like that marketed under the Pyrex brand. Cullet, which is recycled glass, is often used as a raw material as well.
Certain additives called fining agents are often added to glass to reduce the size and frequency of bubbles in glass. Common table salt, sodium sulfate, and various oxide and hydroxide compounds are used for this purpose. Some types of specialty glass contain materials such as fluorine and various metal oxides and phosphates, particularly those of alkaline metals like calcium, lithium and potassium .