How did Manufactured Glass Develop in the Bronze Age?
Glass has evolved throughout its history from an object of rare fascination, to having important decorative qualities, and to becoming critical to both art and daily use. Glass likely has its origin as a byproduct in the production of pottery or metals, as under high temperatures ceramic clays or metal production byproducts, including silica, may vitrify forming a glassy-layer. Perhaps the earliest glass anywhere comes from the ancient Near East or Egypt, by roughly 3500 BC, when temperatures in kilns started reaching higher temperatures as kiln technologies improved.
The Origins of Vitrified Materials
In the Near East and Egypt, glass objects took some time to develop, with several key steps and phases first developed and mastered before other developments occurred. The earliest mass manufacturing of vitrified materials were of faience, which are noticeable on objects by providing luster on objects. Faience forms as a vitrification along the surface of ceramics when a layer of quartz is added and it begins to vitrify; however, unlike true glazes, the temperature for firing does not need to be as high. Different minerals can be added to add colors, such as cobalt or copper elements found in minerals for blue and green colors respectively.
In this early stage, faience does not seem to be a media of art so much but more as decoration for other types of objects, such as beads or ceramic objects. Many objects were still relatively plainly decorated, but their colors imitated precious stones such as lapis lazuli. Faience though begins to be seen as more of an important decorative element for beads and ceramic objects, where by the mid second millennium BC we begin to see more colors and decorative elements added to faience. Egyptian blue, a calcium copper silicate pigment manufactured in Egypt, was often added in Egypt as a way to decorate faience objects and later glazes, which provided a blue color similar to lapis lazuli. Small beads of true glass begin to appear by the 3rd millennium BC, but it is not clear these were even intended objects. Early true glass may have simply been remains from the firing process in the creation of other objects such as metals.
True Glass Objects
Vitrified glazes also become popular in the Late Bronze Age (1600-1200 BC), with tiles, ceramics, and wall decorations now made using this material. Perhaps more significantly for the history of glass is that true glass objects begin to develop and expand more rapidly in the Late Bronze Age , indicating that it no longer was simply an accidental byproduct of manufacturing. Very likely the technology needed for their production, including in the firing process and the utilization of alkaline products to create glass, were now well known. This includes sodium carbonate derived from plants that is used in glass production. In the Late Bronze Age, glass is now utilized to make cups and becomes a type of luxury object traded for by elites and perhaps household consumers, which increasingly had greater appetites for wealthy objects. The Uluburun Shipwreck, which had many rare finds, also contained the world’s earliest intact glass ingots, which were used to make glass objects.
The ingots simply indicate that glass was also sometimes made into a easy transportable form before being shaped into its final product. The shipwreck dates to around the 14th century BC and likely represents finds during a period of active trade in the Eastern Mediterranean between the powers in the Near East and the Aegean. As glass was considered a luxury, it is not surprising that a relatively large quantity of glass was found on the shipwreck. While glass technology improved, it was still an expensive product to make given the material and firing process required.
The Commodification of Glass
In the Neo-Assyrian period, roughly from the 9th to 7th centuries BC, colorless glass seems to have been invented, as the first instruction manual, written on a cuneiform tablet, was found in ancient Nineveh in modern day Iraq in the well-known Ashurbanipal library. In the last half of the first millennium BC, during the Hellenistic period, glass technology improves even more with molds now being used to create larger pieces.  However, the most relevant invention was the development of glassblowing, which used a blow pipe on molten glass (Figure 3). This technique made it much easier to create glass, making it now possible to spread its utilization and making it a much cheaper commodity.
The technique was likely invented somewhere in the Near East by the 1 century BC, perhaps along the Syrian coast. Regardless, it is clear this invention now allows glass to spread rapidly throughout the Mediterranean world, as it made the production time much easier by simply inflating glass and shaping it. The Romans and Sassanian empires, along with India, began to utilize glass substantially in their daily use, including in buildings, mirrors, glass vessels, and as decoration.
Not until the late 17th century in Britain, we begin to see another major invention that further changed how glass was mad. This innovation was the use of coal for burning, making it cheaper to fuel production, and adding lead oxide in order to create crystal glass. This was an important development as it allowed now the industrialization of glassmaking, while making glass durable and clear, establishing the basis for today’s glass production industry.
What we see is that glassmaking had a long history from its earliest appearances as a likely accidental byproduct in the firing of objects. While initially it was a restrict medium, mostly used for imitation of precious objects, it became its own medium of art in the Late Bronze Age in the second half of the second millennium BC. By the late first millennium BC, the technologies of glass improved to allow it to become ubiquitous in regions along the Near East, Mediterranean world, Europe, and much of the Old World. The Romans, Sassanians, and Indian civilizations, in particular, helped to spread the use of glass. In the 17th century, new techniques of glass production allow it to become a product that was more industrialized, while making glass even easier and cheaper to make, including improving its production qualities.
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- For information about the earliest history of glass production, see: Macfarlane, Alan, and Gerry Martin. 2002. Glass: A World History. Chicago: University of Chicago Press.
- For information about faience, its production, and use in the ancient Near East, see: Collon, Dominique. 1995. Ancient Near Eastern Art. Berkeley: University of California Press, pg. 110.
- For information on chemical minerals used for decoration, see: Henderson, Julian. 2013. Ancient Glass. Cambridge ; New York: Cambridge University Press, pg. 163.
- For a history of glass during the Late Bronze Age, see: Henderson 2013: 182.
- For information on the Uluburun Shipwreck and the discovery of complete glass ingots, see: Gordon, Stewart. 2015. A History of the World in Sixteen Shipwrecks. Lebanon, NH: ForeEdge, pg. 39.
- For information on this text that describes the manufacturing technique, see: Moorey, P. R. S. 1999. Ancient Mesopotamian Materials and Industries: The Archaeological Evidence. Winona Lake, Ind.: Eisenbrauns.
- For more information on Hellenistic glass production, see: Henderson 2013: 216.
- For information on the history of glass blowing and its technical developments, see: Carter, C. Barry, and M. Grant Norton. 2013. Ceramic Materials: Science and Engineering. Second edition. New York: Springer.
- For information about glass spread in the Old Word during the late 1st millennium BC and early 1st millennium AD, see: Macfarlane, Alan, and Gerry Martin. 2003. The Glass Bathyscaphe. Paperback ed. London: Profile Books.
- For information about the invention of a lead-based crystal glass, see: Edwards, Geoffrey, and Garry Sommerfeld. 1998. Art of Glass: Glass in the Collection of the National Gallery of Victoria. Melbourne : South Melbourne: National Gallery of Victoria : Macmillan, pg. 101.