There are numerous descriptions of glass for example art glass, stained glass, coloured glass, tiffany glass, carnival glass, uranium glass, frosted glass, etched glass and crystal, and while all crystal is glass, not all glass is crystal. The basic difference is the lead component of the glass, however this varies from country to country so there is no a common rule that can be applied.
Excerpts from the Buying Guide on the Ebay website help explain –
”Overview of Glass and Crystal
………For starters, most people are not aware that “crystal” actually refers to “lead glass.” Below is a quick chemical composition lesson as well as the different types of glass and crystal that can be found on the market.
…… Glass, as a raw material, normally refers to the soda-lime, which makes up over 90 percent of all the glass that is manufactured today. Soda-lime glass is made from lime, soda, and silica. This is the most typical kind of glass for light bulbs, windows, tableware, and figurines, among others. Because its components are readily available in nature, it is also the most inexpensive.
Borosilicate glass, or Pyrex, is composed of silica, boric acid, soda, and other additives. This kind of glass is often used in the laboratory and the kitchen since it is corrosion- and heat-resistant.
Fused quartz glass is made from melting organic quartz crystals in at high temperatures. This type of glass is typically used for laboratory equipment, halogen lamps, and high-end cameras.
When most people talk about bringing out the “crystal,” they are often referring to a type of glass that is made from silica, lead oxide, soda or potash, and other additives. Lead crystal is prized for its durability and decorative properties. It is referred to as crystal because, years ago, the Italian term “cristallo” was used to refer to Murano glass imitations. In the U.S., glasses with a lead monoxide content of 1 percent are automatically categorized as crystal. In Europe, on the other hand, crystal is defined as glass with a lead content that ranges from 10 to 30 percent.
How to Distinguish Between Glasses and Crystal
Aside from the chemical composition, some of the key differences between glass and crystal are thickness – Compared to glass, fine crystal may be thinner or more decorative because the lead content lowers the working temperature of the glass, making it easier to sculpt and allowing it to be more ornately decorated compared to glass. However it also makes the crystal more fragile, breakable, and prone to scratches.
Glasses, especially those made from soda-lime, are cloudy even when held up against the light. Crystal, on the other hand, is known for its clarity. The higher the lead content in crystal, the greater the clarity.
Similar to clarity, crystal’s refractive quality also has a great deal to do with its lead content. Fine crystal, particularly if it has a lead content that ranges from 36 to 70 percent, sparkles in direct sunlight. Optically clear crystal, another type that contains lead, goes a step further and is polished until it is blemish- and distortion-free. This type of crystal is known for the rainbow prisms it creates when placed under the sun. Glass, on the other hand, is more opaque.
Crystal is typically cut and polished in a precise manner. Additionally, it is also smooth to the touch. In contrast, glass tends to be brittle and sharp. One way to tell if a piece is crystal or glass is to feel the facets and overall design of the item. Crystal is much smoother than glass.
Another key difference between glass and crystal is the sound that it makes when tapped. Crystal produces a ringing sound like a “ping” when it is clinked. On the flipside, glass makes a low sound like a “thud.”
And finally, crystal’s lead content also plays a crucial role in its weight. Because lead is a dense metal, crystal is naturally heavier than glass. Glass is often lightweight to hold, while crystal has a solid feel.