Author: Mag_Alef, Contributing Editor
|While much about the origins of glass remains a mystery, some of the oldest pieces on record were retrieved from Mesopotamian excavations dating back to 2500 B.C. The invention of glass, therefore, is attributed to the Mesopotamians, as is the initial spread of glassmaking knowledge throughout the Near East. The glass industry grew steadily through the second and first millennia B.C., until it suddenly expanded near the end of that era, when a new discovery about glass was made.
|THE GROWING MARKET
Glass was used by ancient people for both decorative and practical purposes. Although the first glass items seem to have been beads and other small ornaments, it's use in larger vessels, sculpture, and dishware became popular.
Throughout the Egyptian, Mesopotamian, and Early Roman empires, glass was associated with wealth, and at times it's value rivaled gold. As knowledge of glassworking techniques spread, the supply and variety of products also increased. Eventually it became economically feasible for people outside of royalty to possess glass. This was particularly true during the Roman Age, when glass production became commercialized towards the end of the first millennium B.C.
| INDUSTRY OVERVIEW
It is believed the development of glass was spawned from the pottery and metals industries. For hundreds of years before the advent of glass, pottery workers created beads and small objects out of faience. Faience is a glazed ceramic that's made by combining silica and an alkali in a high-heat process. The metals industry also used high-heat in it's refining and fabrication processes. It was this combined knowledge of materials and pyrotechnics that afforded glass development in the region.
Although the earliest glassworkers likely combined raw materials on a small scale to create the glass they used, overall the industry developed into two distinct branches. There were the glassmakers, few in number, who refined the raw materials into glass cullet, or chunks. The glassworkers, who were widely located throughout the region, used hot and cold working techniques to fashion the cullet into finished glass products.
| GLASS FABRICATION
The main ingredient of glass is silica. Alone it would make a wonderful glass but it requires such a high temperature to melt, that a second ingredient, an alkali, is added to lower the working temperature. Some forms of alkali that were available were soda, potash, and natron. Unfortunately, the addition of an alkali also makes the glass deteriorate in water.
To counteract this problem a third ingredient, lime, is normally added. However, it's speculated that glassmakers of the time were unaware of the necessity of lime. Ancient glass recipes called for only silica and alkali to be used, and crucibles of "bad glass" with little to no lime content, were discovered in factories that existed centuries later. Therefore, it was likely through trial and error that the most notable silica-harvesting operations were located in areas where the sand naturally contained bits of lime-rich crushed shell. It was also likely by accident the glassmakers discovered that certain plants made the best potash. Again, this was because of their high lime content.
Although little evidence exists about the furnaces and crucibles the ancients used for making raw glass, written recipes give us an idea of the manufacturing process. According to cuneiform tablets from c.650 B.C., the Mesopotamians used a two-step process to create their glass. First, the raw materials were crushed and combined to make a frit, or "batch", that was slowly fired over low heat. Next, it was cooled, ground, and fired a second time over high heat, which melted it into a solid piece of glass. The glass was then broken up into chunks, or cullet, and transported throughout the region.
From the time the first vessels were created in the 16th century B.C., glassworkers used brightly colored glasses. Metallic oxides were added to the batch to produce an array of colors. Cobalt produced rich blues; copper produced blues, greens, and reds; manganese produced purples and pinks; and iron, when combined with sulphur, created amber yellows.
Raw glass contains impurities which gives it a greenish to yellowish tinge. The impurities, often iron, are either present in the raw materials, or leach out from the crucibles during the fabrication process. Early glassmakers found they could create clear glass by neutralizing the iron with small amounts of manganese or antimony.
In larger amounts, the addition of antimony made glass opaque. When it was combined with calcium, the result was white opaque glass. Black glass was made by combining dark transparent purples, greens, or blues with a similar translucent glass. The translucent glass prevented light from traveling through, thus giving the illusion of black glass.
Glassworkers employed many techniques to fabricate their products. Casting was initially used to make beads and small sculptures. This process involved filling molds of sand or clay with crushed glass. The molds were then heated to melt and shape the glass. In later years, the Egyptians designed closed molds into which they poured molten glass through a small hole. This enabled them to create a wide variety of vessels, sculptures and other large objects.
The earliest known technique used to make vessels, though, was "core-forming". This involved applying a removable core of organic material, often grass, onto the end of a long iron, clay, or wooden rod. The core end of the rod was then heated, rolled into crushed glass, and put back into the flame to melt the glass.
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