A new MIT led study uses hospital style CT scans to peer inside 5,000 year old copper slag from Tepe Hissar, revealing hidden metal droplets, gas pockets, and complex arsenic chemistry that reshape what we know about early smelting. (CREDIT: AI-generated image / The Brighter Side of News)

By: Rebecca Shavit/Edited By: Joseph Shavit

The Brighter Side

Today, scientists are trying to understand exactly how those early metalworkers did it, even though most of their furnaces and tools have vanished. A new study from MIT offers a fresh way to see into that distant past, using a technology more often found in hospitals than in dig sites.

Unearthing the First Metalworkers

The research looks at copper smelting waste from Tepe Hissar, an important archaeological site in Iran that dates to roughly 3100 to 2900 BCE. At that time, people in the region were already running complex settlements with long distance trade and early metal industries.

Around 5,000 years ago, people in what is now Iran began turning dull stone into shining metal. By heating copper ore until it melted, they learned to pull liquid metal from rock, a skill that helped launch the age of metallurgy and changed daily life, from tools and weapons to jewelry and trade.

Instead of studying rare finished objects, the team focused on slag, the hard, glassy waste left over after ore is melted. Slag may look like trash, but it carries a record of the smelting process inside it.

“Even though slag might not give us the complete picture, it tells stories of how past civilizations were able to refine raw materials from ore and then to metal,” says MIT postdoc Benjamin Sabatini. “The goal is to understand, from start to finish, how they accomplished making these shiny metal products.”

For you, that means the same lump of waste that ancient workers tossed aside can now help reveal how they mastered one of humanity’s first high tech skills.

Slag As a Hidden Archive

When ore is heated to smelting temperatures, it separates into dense metal and a lighter molten waste. The metal pools at the bottom; the slag floats above it and later cools into a solid block. That solid includes leftover minerals from the ore, bits of furnace lining, trapped gas bubbles, and tiny droplets of metal.

In early copper smelting, those mineral leftovers often contained arsenic and other elements that shape how the metal behaves. Over thousands of years, however, rain, soil water, and chemical reactions can leach those elements out or move them around. That makes it hard for archaeologists to read slag like a clean notebook >>>