Glass is one of our most common and often overlooked technologies because it is so common, but that has not always been the case. Glassmaking technology has a history longer than history itself.

Stone-age man shaped obsidian, a volcanic glass created when liquid lava cools too quickly to form crystals, but it took thousands of years to learn how to manufacture and fashion glass from raw materials.

The essential component of glass is silica (silicon dioxide), found in the form of the mineral quartz. Almost all of the modern world’s glass is man-made from quartz sand.

All glasses are based on silica with some type of alkali added to lower the melting point and lime (calcium oxide) added as a stabilizer. Common alkalis are soda (sodium oxide) and potash (potassium oxide). Most common is soda-lime glass, which is used for bottles, jars, everyday glassware and window glass. It is cheap to manufacture and accounts for more than 90% of all glass produced.

Other metal oxides vary the properties of the glass or give it color. Manganese oxide clears the glass and removes the slight green tint caused by the presence of minute quantities of iron oxide. Lead oxide adds weight and brilliance and gives the glass a soft, workable surface.

Boron gives the glass thermal, electrical and corrosion resistance. Borosilicate glasses such as Pyrex are used in chemistry labs, the pharmaceutical industry, for cooking utensils in the home and in bulbs for high- powered lamps.

Optical glasses contain barium, which increases the refractive index, allowing for thinner lenses. The rare earth element cerium absorbs infrared radiation, and various metallic oxides add color: cobalt (blue), manganese (purple), uranium or gold (red), copper (green) and cadmium (yellow).

Legend has it that Phoenician merchants carrying a cargo of saltpeter accidentally discovered how to make glass around 5000 B.C. They supposedly used mounds of saltpeter (sodium nitrate) to rest their cooking pots in the absence of rocks. The heat of the fire melted the nitrate, and when it mixed with the sand on the beach, an opaque liquid formed that hardened into glass.

The Romans began blowing molten glass inside molds sometime between 27 B.C. and A.D. 14. During the first millennium A.D., gradual changes took place in the techniques in producing glass of different qualities and styles, although little is known about the first 800 years.

In the Middle Ages glazing was a luxury, and only royal palaces and churches were likely to have glass windows.

Venice developed into a center of glassmaking in the 13th century. The city passed a protective ordinance that banned imports of foreign glass and glassmakers to ensure that the local craftsmen would preserve the unique style and retain their role as the glassmaking center of the Western world.

The late 16th century saw Venetians migrate to northern Europe where wages were higher. Inevitably the Venetian style mixed with the northern style as glassmaking techniques evolved.

Lead crystal was patented in England in 1674 as the result of a commission to find a substitute for the Venetian-type crystal that was made from quartz and potash. By adding lead oxide instead of potash, the glassmaker produced brilliant lead crystal with a high refractive index.

In the latter part of the 18th century, mechanical technology and the advance of scientific research into the relationship between the composition and properties of glass greatly improved techniques for mass production.

Technology in the 21st century produces an astounding variety of specialty glasses of different compositions and properties such as transparent glass ceramics, infrared-transmitting glass used in night-vision goggles and the tiny threads in the fiber-optic cables that carry information in the form of laser pulses.

Although glassmaking is one of the oldest technologies, the uses and varieties of glass today are more widespread than ever. We take it so much for granted that it has become virtually and truly transparent.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.