Persians Beat the West to Chromium Steel by a Millennium, It Turns Out

Although, it had phosphorus in it too, and by no accident.
Utku Kucukduner

The invention of chromium steel is generally attributed to the West with a history beginning from the late 18th century. It found practical use in the 19th century, and its form as we know today was not around until the 20th century. But new evidence suggests that the invention goes way back to the ancient Persians, about a full millennium back.

Persians Beat the West to Chromium Steel by a Millennium, It Turns Out
Scanning electron microscope (SEM) image of the large steel. Source: Rahil Alipour/UCL

The history of the invention has changed

A recent paper published in the Journal of Archaeological Science details that steel alloys containing chrome were found dating as back as 11th century CE. The steel was probably used in the making of armor, swords, daggers among other items.

On another interesting note, these alloys also contained traces of phosphorus, about 2% to be precise. Phosphorus is used in bringing the melting point of metals in forgery, but on the flip side, it also makes metals more brittle.


The lead author Rahil Alipour, told Gizmodo in a mail, "This particular crucible steel made in Chahak contains around 1% to 2% chromium and 2% phosphorus.” Alipour also noted that this composition would not actually make a steel 'stainless'.

Persians Beat the West to Chromium Steel by a Millennium, It Turns Out
Broken Chahak crucible base where the crucible steel ingot would be solidified. Source: Rahil Alipour/UCL

The discovery was made thanks to a manuscript

The team was led to this discovery thanks to a manuscript written by Persian polymath Abu-Rayhan Biruni titled “al-Jamahir fi Marifah al-Jawahir” or " A Compendium to Know the Gems".

The manuscript led the researchers to Chahak village in Iranshahr, an archeological zone in Iran, which was already known to be an important place for steel production, with evidence of crucible steel production already uncovered.

Persians Beat the West to Chromium Steel by a Millennium, It Turns Out
SEM Image of crucible wall and slag interface and a rounded steel prill trapped in the slag. Source: Rahil Alipour/UCL

"Crucible steel, in general, is a very high-quality steel," Alipour noted and added that "it does not contain impurities and is very ideal for [the] production of arms and armor and other tools."

Biruni's manuscript had a mystery component called rusakhtaj, which translates to the burnt. Later on, this was revealed to be a chromite sand. Chahak excavations led to the discovery of residual charcoal of old crucible slag, which is a byproduct of metal forgery. Radiocarbon analysis revealed that these dated back to between the 10-12th centuries.

Alipour noted, "Previous crucible steel evidence, studied by scholars, belong to crucible steel production centers in India, Sri-Lanka, Turkmenistan, and Uzbekistan. None of these show any trace of chromium. So, chromium as an essential ingredient of Chahak crucible steel production has not been identified in any other known crucible steel industry so far."

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