We often look right past it. Or, at least, through it. Glass is one of the oldest materials humans have manufactured and one of the more interesting.
The origins of glass are lost in antiquity. No one knows exactly where the first glass was made. Indeed, as glass can occur naturally in the form of obsidian from volcanoes, it could be argued that glass pre-dates human history.
But the first deliberate production of glass has been postulated to have occurred around 3000 BCE in the Middle East, possibly in Egypt or Mesopotamia or even along the coast of the Mediterranean or even all three locations at about the same time.
The requirement for soda and for sand has led archeologists to a few likely sites and excavations have discovered very old and serviceable kilns.
Pottery has an even older history and glassmaking could be considered an off-shoot of the pottery industry. The glazing of pottery began around 8000 BCE and glazing is really glass formation on the surface of clay using many of the same basic compounds as in glassmaking. The skills developed for making glazes would transfer to making glass, leading to the notion glassmaking could have originated in a number of locations.
Roman historians, such as Pliny, tell us that the invention of glass was actually an accident. Phoenician traders noticed a clear liquid developed when the blocks of stone they used for cooking interacted with the sand beneath them.
While it is possible this is the original discovery of glass, the intensity of the fire required to melt sand would have meant the fire was unsuitable for cooking. However, some ancient fire pits were routinely used over and over again and developed a form of glazing on their inner surfaces.
In any case, what we do know is that Egyptian glassmakers were producing glass vessels by 1500 BCE. The first manual we know about on glassmaking appeared around 650 BCE written on stone tablets. And we also know the techniques for glassmaking were spread throughout the Mediterranean by Phoenician traders.
Early Egyptian craftsman used a method called "core-forming" for making vessels. A core of compacted sand, clay, and dung was dipped into a pot of molten glass and then tipped upside down so that the glass flowed over its surface. The surface could be made smooth by rolling the vessel on a flat surface.
The glass was allowed to harden and the core scrubbed from the inside, resulting in a semi-clear vessel. This technique is still used today albeit in a slightly different form and not just for making glass objects. The disadvantage to the method is that the core must be re-built or sculpted for each individual piece and removing the core sometimes resulted in debris trapped on the surface.
A major advance in glassmaking took place early in the first century when glass blowing was discovered. The glass "gather" at the end of the tube is literally blown out by the glassmaker in much the same way that we now blow bubbles out of gum. The resulting bulb could be fashioned by rolling or cut and re-attached to generate quite intricate works. Modern glass blowers still employ essentially the same techniques.
Glass blowing also allowed for the mass production of uniform items. Instead of free blowing the glass, the gather could be placed inside a mold and the glass blown into the shape repeatedly, generating a uniform bottle or cup.
Modern machinery is now used to blow glass into molds to make a wide variety of glass bottles and jars. The distinctive ridge down the side of a jar is a product of this method as it forms where the two halves of the mold meet.
Glass blowing was also used to generate sheet glass. A large bubble was blown and allowed to sag in on itself, generating a flat sheet of glass. A square sheet could then be cut but the distinctive nipple where the rod was attached remained. As such, the glass was transparent to light but not particularly good as a window for looking out of.
Sheet glass without distortions was made by rolling the blown glass into a cylinder and then cutting off the ends. A slice down the length of the cylinder, and some careful manipulation, results in a large flat sheet. With the invention of better methods for making flat glass, windows really came into their own as architectural features.
Modern sheet glass is made by floating molten glass on a large pool of liquid tin. It produces a much flatter glass with few defects.
In the end, though, all glasses are really just a flux of silica and a few other components melted to generate a hard, brittle, transparent, amorphous solid. But despite its simplicity, it is difficult to imagine what our lives would be like without it.
