Features ingots, shipwrecks, and international color trade, using modern archeology and materials science to trace the rich history of materials

Today, glass is something on ordinary kitchen shelves. But early in its history, glass was gleaming to the king.

Thousands of years ago, the pharaohs of ancient Egypt surrounded themselves with these things even after their deaths, leaving behind amazing specimens for archaeologists to discover. In the tomb of King Tutankhamun, there is a decorative writing palette and two blue headrests made of solid glass, which may have supported the heads of sleeping royals. His funeral mask is inlaid with blue glass inlays, which alternately decorate the king's face with gold.

Andrew Shortland said that in a world of pale yellow, brown and sand tones filled with more practical late Bronze Age materials, glass — full of blue, purple, turquoise, yellow, red, and white — would Offering the most eye-catching colors other than gems, archaeologists at Cranfield University in Shreveham, England. In the material grade, glass will be slightly lower than silver and gold, and its value will be as high as gems.

However, many questions about precious materials still exist. Where did glass first appear? How did it work and color, and spread in the ancient world? Although there are still many mysteries, in the past few decades, materials science and technology and reanalysis of unearthed cultural relics in the past have begun to fill in the details.

In turn, this analysis opens a window for understanding the lives of artisans, merchants, and kings in the Bronze Age and the international connections between them.

Glass, whether ancient or modern, is a material usually made of silicon dioxide or silicon dioxide, which is characterized by its atomic disorder. In crystalline quartz, atoms are fixed at regular intervals in a repeating pattern. But in glass, the same component—a silicon atom bound to oxygen—is arranged upside down.

Archaeologists discovered that the history of glass beads can be traced back to the third millennium BC. The glazed surface based on the same material and technology is earlier. But in the late Bronze Age-between 1600 and 1200 BC-the use of glass seems to have really started in Egypt, Mycenae, Greece, and Mesopotamia, also known as the Near East (located in what is now Syria and Iraq).

Unlike today, the glass of that era was usually opaque and saturated in color, and the source of silica was crushed quartz pebbles, not sand. The clever ancients figured out how to lower the melting temperature of crushed quartz to the temperature reached by Bronze Age furnaces: They used the ashes of desert plants, which contained large amounts of salt, such as sodium carbonate or bicarbonate. These plants also contain lime-calcium oxide-to make the glass more stable. Ancient glass manufacturers also added materials that gave the glass color, such as dark blue cobalt or yellow lead antimonate. These components fuse in the melt, providing the chemical clues researchers are looking for today.

Mark Walton, a materials scientist at Northwestern University in Evanston, Illinois, said: "We can start analyzing the raw materials used in glass production and then come up with where in the world it came from." He is an article on materials science and materials in 2021. Research the archaeological artifacts and artworks in the annual review.

But these clues only let researchers know so far. When Shortland and his colleagues investigated the origin of glass about 20 years ago, glass from Egypt, the Near East, and Greece seemed to have chemical similarities, which were difficult to distinguish based on the technology available at the time.

Blue glass is an exception, thanks to the Polish-born chemist Alexander Kaczmarczyk, who discovered in the 1980s that elements such as aluminum, manganese, nickel, and zinc were marked with cobalt, giving the glass a dark blue color. By examining the relative amounts of these substances, Kaczmarczyk's team even traced the cobalt ore used to color the blue to its mineral origin in a specific Egyptian oasis.

From where Kaczmarczyk stopped, Shortland set out to understand how the ancient Egyptians handled this cobalt ore. This material is a sulfate-containing compound called alum and does not melt into the glass. But in the laboratory, Shortland and his colleagues reproduced the chemical reactions that craftsmen in the late Bronze Age might have used to make compatible pigments. They created a dark blue glass, which is actually similar to Egyptian blue glass.

In the first few years of this century, a relatively new approach provided more insights. This technique is called laser ablation inductively coupled mass spectrometry or LA-ICP-MS, which uses a laser to remove tiny material spots that are invisible to the naked eye. ("For a museum, this is more acceptable than taking a big hammer out," Shortland said.) Then it uses mass spectrometry to measure a set of elements, creating a chemical fingerprint of the sample.

Based on this method, in 2009, Shortland, Walton and others analyzed the late Bronze Age glass beads unearthed in Greece. Some researchers suggested that these glass beads have their own glass production workshop. Analysis shows that Greek glass has the signature of the Near East or Egypt, supporting Greece's view that it imports glass from these two places. Although it may have been useful for glass, it is not made locally. Egyptian glass has higher lanthanum, zirconium and titanium content, while Near East glass has higher chromium content.

But where was glass first born? For at least 100 years, researchers have been arguing about two main competitors: the Near East and Egypt. According to some exquisite glassware well-preserved around 1500 BC, Egypt was initially favored. But in the 1980s, after excavators discovered a large amount of glass in Nuzzi, the provincial capital of the late Bronze Age in modern Iraq, the researchers placed their bet on the Near East, which is believed to date back to the 1500s BC.

However, at about the same time, a re-analysis of the archaeological text revealed that Nuz was 100 to 150 years younger than estimated, and that the Egyptian glass industry at that time appeared to be more advanced—again beneficial to Egypt.

But this is not the end of the story. Glass can degrade, especially under humid conditions. With the help of an almost ideal preservation environment in the desert, the objects in Egyptian tombs and towns have been preserved for thousands of years. On the other hand, Near Eastern glass from tombs in the floodplain of Mesopotamia is more susceptible to water attack, which leaches stable compounds and turns the glass into flake powder.

This deteriorated glass is difficult to identify and cannot be displayed, which means that many Near East glasses may be missed. "I think a lot of glass has actually disappeared," Shotland said. "Compared with other things, the early excavation work paid less attention to this kind of sheet front glass."

Bottom line: "At the moment you can't really decide which is the earliest," Shortland said.

It is even tricky to analyze where the glass is made. This is partly because materials are often exchanged, both as finished products and as unprocessed glass to be processed into beads or vessels.

Thilo Rehren, an archaeological materials scientist at the Cyprus Research Institute in Nicosia, has studied the craftsmanship behind Tutankhamun's tombs and other objects. He said that glass helped to link ancient empires together. He said that the kings sent materials to other rulers, hoping to get goods or loyalty in return. The ancient inventory of the late Bronze Age revealed the exchange of ivory, gems, wood, animals, people, etc. Although the role of glass in this gift and tribute convention is not fully understood, the composition of cultural relics also supports glass exchange.

In a glass bead necklace unearthed in Gurob, Egypt, the area was thought to be a harem. Shortland and his colleagues discovered the chemical characteristics associated with Mesopotamia: relatively high Chromium content. The position of the beads suggests that this golden gift might have been given to Pharaoh Thutmose III and a Near East woman who became the king's wife. With the chemical reaction of the case, “we are only now beginning to see some of this exchange going on between Egypt and other regions,” Shotland said.

In the early 1980s, divers discovered the mother vein of this exchange in a shipwreck off the coast of Turkey, which came from 1300 BC and was called the Uluburun shipwreck. Caroline Jackson, an archaeologist at the University of Sheffield in the United Kingdom, said that analysis of its content reveals the global economy. It may be a Phoenician ship during the gift-giving expedition. The ship hauled goods from all over: ivory, copper, tin, and even amber from the Baltic Sea. The excavator took a large amount of colored glass from the sunken ship-175 unfinished glass blocks, called steel ingots, used for glass processing.

Most of the ingots are dark blue with cobalt, but there are also purple and turquoise ingots on board. Jackson and her colleagues cut small fragments from three glass ingots and reported in 2010 that the original glass block originated in Egypt based on the concentration of trace metals.

Another reason why it is tricky to determine where the glass is made is that there is almost no waste in the process. "You get a finished product, of course, it will enter the museum," Lei Lun said. About 20 years ago, this prompted him and archaeologist Edgar Pusch to work in a flea-infested excavation house in the Nile Delta, carefully studying pottery, and looking for signs of an ancient glass-making workshop. The site is close to what is now Qantir, Egypt, and was the capital of Pharaoh Ramses II in 1200 BC.

Rehren and Pusch found that many containers have a lime-rich layer that acts as a non-stick barrier between glass and ceramic, making the glass easy to lift. Some of the suspicious glass containers-including a reusable beer can-contained white, frothy semi-finished glass. Rehren and Pusch also linked the color of the pottery to the temperature they endure in the furnace. At a temperature of about 900 degrees Celsius, the raw materials may have melted to make semi-finished glass. But some crucibles are dark red or black, indicating that they have been heated to at least 1000 degrees Celsius, which is enough to complete the melting of the glass and uniformly color it to produce glass ingots.

Some crucibles even contain residual red glass, colored with copper. "We were able to confirm the evidence of glass manufacturing," Rehren said. "No one knows what it should look like."

Since then, Rehren and colleagues have found similar evidence of glass manufacturing and ingot production in other locations, including the ancient desert city Tell el-Amarna, or Amarna for short, which was briefly the capital of Akhenaton in the 1300s. They noticed an interesting pattern. In Amana's crucible, only shards of cobalt blue glass appeared. But in Qantir, where red copper was also used to make bronze, the crucibles excavated mainly contained red glass shards. ("Those people know exactly what to do with copper—it's their special skill," Raelen said.) In the 1920s, Egyptian Egyptologist Mahmoud Hamza even unearthed it in Qantir A large corroded red glass ingot. At a location called Lisht, the crucible containing the glass remains mainly contains turquoise fragments.

Rehren said the monochrome findings at each location indicate that the workshop specializes in one color. But artisans can obviously touch the rainbow. In Amarna, the glass rods excavated from the site — possibly made from remelted ingots — come in a variety of colors, supporting the idea that colored ingots can be transported and traded for glass processing in many places.

Archaeologists continue to pursue the story of glass in Amarna—and in some cases, more carefully repeat the explorations of earlier archaeologists.

In 1921-22, a British team led by archaeologist Leonard Woolley (famous for his excavations in Ur) excavated Amarna. "Frankly, he made a mess of things," said Egyptologist and archaeologist Anna Hodgkinson at the Free University of Berlin. In a hurry and focusing on more gorgeous discoveries, Woolley did not do due diligence while recording the glass. During the excavations in 2014 and 2017, Hodgkinson and his colleagues struggled to find the missing debris.

Hodgkinson's team found glass rods and shards in the Amarna area they excavated. Some were unearthed near relatively low-status households without kilns, which is a headache because of the supposed role of glass in symbolizing status. Inspired by older Egyptian art, which depicts two metal workers blowing into a fire with pipes, archaeologists want to know if a small fire can be used to process glass. They sweat and stink around the flames and find that they can reach temperatures high enough to form beads in fires that are smaller than those usually associated with glassware. Hodgkinson said that early excavators may not find such a small fireplace, so the glass processing may not be as unique as researchers have always believed. Hodgkinson speculated that perhaps women and children were also involved, which reflected the many hands needed to maintain the fire.

Rehren has also been rethinking the use of glass because the commercial towns in the Near East have a large amount of glass and it is shipped to Greece in large quantities. "To me, it doesn't smell like a strictly controlled royal commodity," he said. "I believe that in 5 to 10 years, we will be able to prove that glass is an expensive and professional commodity, but not a strictly controlled commodity." Elite, but not just for the royal family.

Researchers have also begun to use materials science to track potential color transactions. In 2020, Shortland and colleagues reported that isotopes (versions of elements with different atomic weights) are used to trace the source of antimony, an element that can be used to produce a yellow color or make glass opaque. "Most early glass-that was the beginning of glass manufacturing-contained antimony," Shotland said. But antimony is very rare, which makes Shortland's team wonder where the ancient glassmakers got it.

They found that the antimony isotopes in the glass match the current Georgian antimony sulfide or antimonite-containing ores in the Caucasus region-one of the best evidences of international color trade.

Researchers are continuing to study the era of the first glass. Although Egypt has attracted a lot of attention, archaeologists can still excavate many sites in the Near East to find new clues. Due to modern restrictions on moving objects to other countries or even remote locations for analysis, Hodgkinson and other archaeologists are working hard to apply portable methods in the field and cooperate with local researchers. At the same time, many old objects may generate new clues when they are analyzed again using more powerful techniques.

As we continue to shape the historical knowledge of glass, Rehren cautions against the certainty of conclusions. Although archaeologists carefully infer the importance and legend of the cultural relics with the help of records and known cultural backgrounds, only a small part of the materials that were once scattered at any particular location can survive today. "You will get conflicting information, conflicting ideas," he said. All these pieces of information, glass, "you can assemble different photos in different ways."

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