All crystal is a form of glass--but not all glass can be called crystal. In the world of art glass, "cut glass" refers to a decorative technique and is a very complex process in which crystal, which is glass with lead oxide added, is used. Using special equipment, contemporary companies can create and replicate pieces which are not crystal quality but look very similar. In discerning the quality of a given piece, collectors and artists evaluate differences between glass and crystal by determining processing methods, composition and appearance.
The Cut Glass Process
John, C. Roesel of the American Cut Glass Association defines cut glass as "glass that has been decorated entirely by hand by use of rotating wheels." To prevent shattering, Roesel says, glass is softened by adding lead oxide, the key component in crystal. Traditional cut glass, therefore, is actually crystal. However, collectors of lead crystal focus primarily on the quality of the crystal itself. A cut glass collector is interested in the specific cutting patterns, designs, and producers of cut pieces (usually from a given period in history).
Composition of Crystal
Opinions about the exact percentage of lead oxide required for crystal vary. One contemporary crystal manufacturer says the glass must contain 24 per cent lead.
Manufacturers all agree, however, that crystal must contain some percentage of lead oxide. This percentage is an important factor in evaluating the quality of a given object. One explanation for the discrepancy of lead content is that shortages of lead and manpower during World War I resulted in skyrocketing prices as well as a decline in quality which, many collectors and artists claim, has never been fully restored.
Cut Glass Processing and Lead Crystal
Prior to World War I, in what is termed "The Brilliant Period," (1876-1917), all cut glass was considered crystal.
Since the war, manufacturers have been able to cut lesser glass with special equipment, including acid washes and moulds, to replicate cut-glass patterns. Pieces are likely to be called "cut crystal" if the object contains lead oxide and has been manufactured after the Brilliant Period. Usually, a cut crystal piece made before the Brilliant Period will be called "cut glass," but, after this time period, collectors will make a distinction to indicate whether lead oxide has been added, calling a piece "cut crystal" if the lead additive is evident.
Differences Between Glass and Lead Crystal
Leaded crystal can be identified by the specific bell-ring tone that it makes when you "ping" it with your fingers. Because of the lead oxide, crystal weighs much more for its size than an identical item made from glass. Crystal is clearer and more brilliant than glass, and any added colour tends to have a richer, deeper and brighter sparkle. Crystal is not always decorated by the cutting process.
Historic Periods In Cut Glass
Collectors of cut glass are largely interested in pieces made during the Brilliant Period. From 1897 to about 1915, American artists and manufacturer's created some of the world's best cut glass. These objects were cut from pieces of lead crystal with higher lead contents and are known for their brilliance and workmanship. Waterford and Libby, some of the better-known makers of the period, are still in existence today.