Glass Value, Price, and Jewelry Information
Glass has been used in jewelry for thousands of years. By itself, glass is brittle and unimpressive with very little color or brilliance. However, with additives, it can become more colorful, lively, and durable.
All glass has low value. All sold by piece, rather than by carat.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Glass|
|Colors||All and colorless|
|Fracture||Conchoidal, inclusions may cause splintery or granular fractures|
|Hardness||5 - 6|
|Specific Gravity||2.30 - 4.50|
|Enhancements||Coatings, common, easily scratched.|
|Transparency||Transparent to Opaque|
|UV Long||Not diagnostic|
|UV Short||Not diagnostic|
|Absorption Spectrum||Not diagnostic.|
|Phenomena||Aventurescence, adularescence, asterism, chatoyancy, color change, iridescence, orient (by adding coatings), play of color (simulates opal but different mechanism).|
|Formula||Primarily silica (SiO2) with many additives|
|Optics||Isotropic. May show anomalous birefringence.|
|Etymology||From the Proto-German glasam|
Glass is essentially silicon dioxide (SiO2), and quartz sand is its primary source.
This article deals exclusively with the commercially or artisanally created varieties of glass used to simulate gemstones. Natural glasses exist, such as obsidian and tektites. These materials are described in separate articles.
When added to glass, metals and minerals can create many colors. These additives also have other effects. For example, lead is frequently added to raise the refractive index (RI) and dispersion. It also makes the material more durable, a feature characteristic of lead crystal glassware. (Of course, crystal is an inappropriate adjective for amorphous glass). Lead also increases the specific gravity (SG) of some glass varieties. Gemologists may also encounter lead glass not only in simulated gemstones but also in the hemicylinders of refractometers.
Glass can be made and shaped to appear like almost any type of gem. However, its physical and optical properties usually differ significantly from those of the natural gemstones it may resemble.
With just a loupe, gemologists may find many telltale signs of manufactured origins. Glass usually contains inclusions, such as swirl marks and round bubbles, not found in natural gems. Glass pieces molded to appear faceted may also have mold marks, rounded facet edges, and concave facets. These form as the pieces shrink when cooling. (Concave facets are otherwise very rarely encountered in faceted gems). However, note that some glass varieties can actually be faceted, so these wouldn’t necessarily show round edges or concave facets.
Manufactured glass may show an uneven surface sometimes called “orange peel.” However, some natural gems can also show such an effect.
Since amorphous glasses conduct heat much faster than crystalline materials, they will feel warm to the touch, much warmer than most of the gems they may resemble.
Although glasses, both synthetic and natural, are singly refractive, they frequently show anomalous double refraction (ADR).
Trade Names and Varieties
Many glass pieces are indeed shaped like traditional finished gems and given colors and other optical effects that imitate natural stones. Jewelry makers may use such pieces as accents or even center stones in their projects. However, as long as the pieces are disclosed as glass to consumers, this isn’t a deceptive practice.
Sometimes, glasses may be shaped and designed to look wholly unlike traditional cut gems, and these may be used for ornamentation or worn as jewelry, too.
You may encounter many trade names and varieties of glass and glass treatments. The following are some of the most well-known.
Also known as chaton foils, colorless glass with foil backs.
A trade name for a facetable manufactured glass made in Australia.
A glass-like ceramic used as a glaze on pottery as well as for making beads and other objects. The Ancient Egyptians famously used this material as a turquoise simulant.
A black, opaque glass used to imitate jet, especially during its fashion heyday in the Mid-Victorian Era. Although glass usually feels warmer to the touch than the gems it may simulate, natural jet (another amorphous material) actually feels warmer than glass. Despite the name, most French jet came from Bohemia in what is now the Czech Republic.
Most likely invented in Italy in the 17th century and originally named avventurina, after the Italian a ventura for “by chance,” this material actually introduced the term “aventurescence” into mineralogy. Please note that nowadays the name “aventurine” is also applied to natural varieties of quartz and feldspar that display aventurescence. Goldstone may simulate these natural gem varieties.
A rare variety of facetable manufactured glass. Consult the laserblue gem listing for more information.
Common glass, like that used for bottles, with low RI and dispersion, used to imitate gemstones.
Historically, clear rock quartz crystals backed with foil, used to imitate diamonds. Nowadays, the name may also apply to leaded glass pieces backed with foil or metallic paint. The backings can add brilliance and color to the glass.
Purplish glass or quartz pieces sold as opal simulants and sometimes misidentified or misrepresented as rare, faceted scorodites. Sometimes misleadingly referred to as “scorolite opal.”
Discarded manufactured glass pieces weathered for years by ocean water until washed onto beaches all over the world. As known as “beach glass” or “drift glass,” this material has become a popular jewelry item.
Glass used to imitate opal. Silicate glass with Na, Mg, Al, and Ti; hardness = 5.5-6.5; no cleavage; conchoidal fracture; tough tenacity; SG = 2.41-2.51; N = 1.49-1.53 (may show a kaleidoscopic effect in crossed polars).
Historically, a type of facetable glass with a high RI, developed by the Viennese goldsmith Joseph Strasser in 1758 and used as a diamond simulant. Today, the term may also refer to glass with a high lead content or be used as a synonym for rhinestone.
Also known as Vaseline glass, uranium glass gets it typically green to yellow and yellow-green color from the addition of uranium dioxide. This material enjoyed some popularity from the mid-19th century until World War II. Uranium glass will fluoresce vividly under ultraviolet light (UV). Most of the housewares and jewelry items made from this material are safe to handle. However, it may be prudent to have the radioactivity of any piece measured in a laboratory, especially if you’re considering cutting it.
Also known as Imori Stone (after its inventor, Dr. S. Imori) and Kinga Stone, this glass was developed in Japan in the mid-1950s. Its production was discontinued in 1985, and the exact manufacturing process remains unknown. This complex silicate glass can show many colors. Some pieces will display chatoyancy, due to their fibrous structure. It has been used as a simulant for many gemstones, including blue pectolite.
Green Victoria Stone used to simulate jade may be called “metajade.”
- Nephrite simulant: N = 1.61; SG = 3; hardness = 6.
- Jadeite simulant: N = 1.50; SG = 2.80; hardness = 6.
You can easily identify faceted glass with foil backs (rhinestones) by looking at their pavilions. They’re usually opaque and show a different color than you see face up. Richly colored rhinestones are used very frequently in costume jewelry.
There’s no single best way to clean glass jewelry. Some pieces have treatments which may react poorly to typical household glass cleaners or mechanical cleaning systems, especially surface coatings and foil backs.
Follow these instructions for cleaning rhinestones.
Since household dust has a hardness (7), which exceeds that of most glass gemstones, use a lint-free cloth for manual cleaning, and resist the urge to just scrub away dirt or grime.
Mild soap and warm water should be safe for most non-treated pieces.
Although glass may be inexpensive and is certainly not rare, antique pieces may have historical or sentimental value. Furthermore, some manufacturing processes no longer exist, so replacing something like a Victoria Stone, for example, may prove very difficult. Consult with an antique specialist for the best way to clean such pieces.