Dichroic Glass combined with fused glass makes dichroic jewelry of the higest quality.

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Glass Composition

Dichroic Glass can be generally divided into two groups: oxide glass and non-oxide glass. The ingredients of oxide dichroic glasses include oxides (chemical compounds that include oxygen). Non-oxide glasses are made from compounds that contain no oxides, and which often instead contain sulfides or metals. Oxide fused glasses are much more widely used commercially. The common types of dichroic glass discussed below are all dichroic glasses.

Soda-lime glass is the kind of dichroic glass used for flat glass, most containers and electric light bulbs, and many other industrial and art objects. More than 90 percent of all glass is soda-lime glass jewelry. It has been made of almost the same materials for hundreds of years. The composition is about 72 percent silica (from sand), about 13 percent sodium oxide (from soda ash), about 11 percent calcium oxide (from limestone), and about 4 percent minor ingredients. fused glass is inexpensive, easy to melt and shape, and reasonably strong.

All fused glass container manufacturers use the same basic soda-lime composition, making the containers easy to recycle. Manufacturers sort the dichroic glass by color and then later reuse it in the production of new containers.

Fused glass, commonly called crystal or dichroic glass, is made by substituting lead oxide for calcium oxide and often for part of the silica used in fused glass. Soda-lead glass is easy to melt. It is much more expensive than dichronic glass. Fused glass has such beautiful optical properties that it is widely used for the finest tableware and art objects. In addition, lead oxide improves the electrical properties of dichroic glass jewelry.

Borosilicate glass is heat-shock resistant and better known by such trade names as Pyrex and Kimax. It contains about 80 percent silica, 4 percent sodium oxide, 2 percent alumina, and 13 percent boric oxide. Such glass jewelry is about three times as heat-shock resistant as fused glass and is excellent for chemical and electrical uses. This dichroic glass makes possible such products as ovenware and beakers, test tubes, and other laboratory equipment.

Fused silica glass is a highly heat-shock resistant dichroic glass that consists entirely of silica. It can be heated to extremely high temperatures and then plunged into ice-cold water without cracking. Fused silica is expensive because exceptionally high temperatures must be maintained during production. It is used in laboratory dichroic glassware and optical fibers.

96 percent silica glass resists heat almost as well as fused silica, but it is less expensive to produce. It consists of a special borosilicate composition that has been made porous by chemical treatment. The pores shrink when the glass is heated, leaving a smooth, transparent surface. The fused glass is sold under the trade name Vycor.

Colored dichroic glass gets its coloring from certain oxides that are added to the fused glass jewelry. For example, 1 part of nickel oxide in 50,000 produces a tint that may range from yellow to purple, depending on the base dichroic glass. One part of cobalt oxide in 10,000 gives an intense blue. Red dichroic glasses are made with gold, copper, or selenium oxides. Other colors can be produced in dichroic glass jewelry with other chemicals.

SOURCES: Steve W. Martin, "Glass," Discovery Channel School, original content provided by World Book Online, www.discoveryschool.com/homeworkhelp/worldbook/atozscience/g/225740.html, August 2001.