HOW TO MAKE GLASS ~

The properties of glass are varied by adding other substances commonly in the form of oxides, i.e., lead for brilliance and weight, Boron for thermal and electrical resistance, Barium to increase the refractive index(optical), and Cerium to absorb infrared rays. Metallic oxides to impart or decolorize.

All sand on earth has some traces of "iron oxides" and the presence of the iron produces glass of an aqua color in hues ranging greenish to blue. Around 1673, the English used ground flint to produce "clear glass." In 1674, "lead glass" was invented which made glass clear by adding 25% red lead to the batch. We now call this "lead crystal" and explains how the term "crystal clear" came about. Both of these methods were expensive and, due to economic reasons, most old glass is found in aqua. Iron-slag was used in glass recipes from the 1600's to approximately 1860 or so. This made the glass a dark olive green or "black glass."

The year 1880 saw a rise in the demand for "clear" food preserving containers. At this time, manganese was added to the batch to make glass clear. The amount of manganese in a given batch, along with the amoung of ultra-violet rays the glass was exposed to, will cause glass to become purple in various degrees of density. This color was termed sca (sun-colored amethyst). Manganese was most commonly used from 1880 through 1914. WW1 saw our (U.S.) supply cut off by Germany. It was at this time Selenium was discovered and used as a "decolorizing" agent to make glass clear. Glass made with Selenium, that is exposed to ultra-violet light rays, will become either straw, wheat, or honey colored. Clear glass produced from 1914 through 1940 is most apt to change to these colors due to the Selenium content. Modern technology can now separate the iron-oxide out of the sand.

Recipe for Glass...

1. Sand-silca/fine sand or pulverized sandstone

2. Soda (wood ashes)

3. Potash (alkali) lowers the melting point. *used for finer glass

4. Lime (a stabilizer)

Additonal metallic oxides will produce true colors of blue, green, yellow, brown, purple, etc.