How and When Did People Start Making Glass?
The typical home contains dozens of items made of glass, from canning jars in the pantry to decorative knickknacks on the mantel to the windows and doors that insulate our living spaces and filter light. Despite the surge of plastic products following World War II, this delicate translucent material has maintained its essential place in our homes and daily routines.
Historically, the glass items that we now take for granted were highly coveted luxuries, accessible for a time only to the rich and royal. The evolution of glassmaking has transformed the material from an exclusive work of art to an ubiquitous aspect of modern living. But when — and how — did humans first learn to make this valuable, versatile material?
What Is Glass Exactly?
To understand how glass is made, we must first understand what glass is and how it’s different from other materials. Rather than a single, uniform substance, glass is an unusual state of matter that looks like a solid but acts like a liquid. The formation of glass occurs when a molten substance is cooled so rapidly that its atoms are unable to organize into the latticelike crystalline structure characteristic of a solid. Likewise, these atoms also lack the ability to move randomly, as they would in a liquid. Because of the unusual properties of its atoms, glass is in a distinctly unique category of its own, neither fully solid nor fully liquid, referred to as a rigid liquid or an amorphous solid.
While we typically think of glass as a human invention, it also occurs naturally. Lightning strikes, meteorite impacts, volcanic eruptions, and even some sea creatures can produce natural glasses that are similar in composition to human-made glass. Natural glass is formed when silica-rich sand or rocks are heated to high temperatures and rapidly cooled. Examples include obsidian, created by the rapid cooling of volcanic lava; tektites and impactites, formed by the impact of meteorites; fulgurites, created by lightning striking sand; and even the siliceous (silica) skeletons produced by certain types of sea sponges and algae.
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Glassmaking Is Thousands of Years Old
Ancient glass was made from three primary ingredients: sand (silicon dioxide or silica), an alkali oxide (typically soda ash or natron), and lime. When combined and heated to 2,400-2,700 degrees Fahrenheit, the ingredients fused to form glass.
The earliest evidence of glassmaking includes objects such as beads, pendants, and inlays that were cast in open molds, but glass may have initially occurred as an accidental byproduct in the workshops of Bronze Age metalworkers and ceramicists. While archaeologists have found glass artifacts produced by the Egyptians and Phoenicians dating back to the second millennium BCE, current theory suggests that the first human-made glass dates back even further, to Mesopotamian craftsmen during the third millennium BCE, some 4,000 to 5,000 years ago.
The Birthplace of Glassmaking
Researchers have long debated the birthplace of glassmaking, in part because glass products, as well as the raw materials used for the glassmaking process, such as blocks of colored glass called ingots, were frequently exchanged along trade routes. But advances in archaeology and chemistry have helped researchers better pinpoint the origins of glassmaking to ancient Mesopotamia (modern-day Iraq).
Situated between the Tigris and Euphrates rivers, Mesopotamia was well suited for trading its glass materials and glassmaking knowledge. By the second millennium BCE, artisans had developed sophisticated techniques to shape glass and create vessels. One such method, called core forming, involved creating a hollow vessel by covering a mud core with glass and then removing the hardened mud. Core-formed objects have been found in Mesopotamia, as well as Egypt, where glassmaking also flourished.
Glass trading between Egypt and Assyria was mentioned in the Amarna Letters, a set of cuneiform clay tablets dating to the 14th century BCE that were excavated in the ancient desert city of Amarna, in modern-day Egypt. Not surprisingly, chemical analysis of glass excavated in Amarna found the glass was of Mesopotamian origin. Similarly, the presence of cobalt glass beads in Scandinavian Bronze Age tombs has provided evidence of a complex trading system linking Mesopotamia and Egypt with the Nordic Bronze Age cultures. These findings highlight the extensive trade networks of the ancient world, and demonstrate the far-reaching influence of Mesopotamian glassmaking, even as other cultures began to adapt and develop their own glassmaking methods.
