Elements of Color in Stained and Colored Glass
Cobalt, Gold, Lead, Copper and Uranium Have Been Used to Color Glass
|Color is the most obvious property of a glass object. It can also be one of the most interesting and beautiful properties. Although color rarely defines the usefulness of a glass object it almost always defines its desirability.|
The Colored Glass Recipe:
The earliest people who worked with glass had no control over its color. Then, through accident and experimentation glass makers learned that adding certain substances to the glass melt would produce spectacular colors in the finished product. Other substances were discovered that, when added to the melt, would remove color from the finished project.
The Egyptians and the Romans both became expert at the production of colored glass. In the eighth century, an Arab chemist known as "Gerber" recorded dozens of formulas for the production of glass in specific colors. Gerber is often known as the "father of chemistry" and he realized that the oxides of metals were the key ingredients for coloring glass.
The Glass Color Palette:
Once the methods of colored glass production was discovered, an explosion of experimentation began. The goal was to find substances that would produce specific colors in the glass. Some of the earliest objects made from glass were small cups, bottles and ornaments.
Religious organizations were among those who provided incentive to the early glass artisans. Stained glass windows became very popular additions to churches and mosques over 1000 years ago. These artists needed a full palette of colors to make a realistic stained glass scene. This search for a full palette fueled research and experimentation to produce a vast array of colors.
Colors of Duration:
Then, another problem was discovered. Many of the glass colors did not stand up to year-in, year-out exposure to the direct rays of the sun. The result was a stained glass scene of deteriorating beauty. Some colors darkened or changed over time, while others faded away.
Research and experimentation continued in an effort to meet the need for colors of duration. Eventually a full palette of fairly stable colors was achieved.
Metals Used to Color Glass:
The recipe for producing colored glass usually involves the addion of a metal to the glass. This is often accomplished by adding some powdererd oxide, sulfide or other compound of that metal to the glass while it is molten. The table below lists some of the coloring agents of glass and the colors that they produce. Manganese dioxide and sodium nitrate are also listed. They are decoloring agents - materials that neutralize the coloring impact of impurities in the glass.
Widely Known Glass Colors:
Some colors of glass are widely known. Perhaps the best example of this is "cobalt blue" that is produced by adding cobalt oxice to the glass melt. "vaseline glass" is a fluorescent yellow-green glass that contains small amounts of uranium oxide. "Ruby gold" and "cranbery glass" are red glasses produced by the addition of gold. "Selenium ruby" is a red color caused by the addition of selenium oxide and "Egyptian blue" is produced by the addition of copper.
Minerals: The Keys to Coloring Glass
The sources of the oxides, sulfides and other metals compounds used to color glass are minerals. The keys to beauty often come right from the Earth.
Many thanks to Geology.com for this article!