Wootz Steel: Making Damascus Steel Blades

2,400 Year Old Crucible Process of Iron Mongering

Electron Micrograph of Etched Wootz Steel Sample
Electron micrograph of a deeply etched wootz sample illustrating the fine precipitation probably formed by self-tempering of martensite during the final cooling. Published in Durand-Charre et al. 2010. Courtesy Institut National Polytechnique

Wootz steel is the name given to an exceptional grade of iron ore steel first made in southern and south-central India and Sri Lanka perhaps as early as 400 BCE. Middle Eastern blacksmiths used wootz ingots from the Indian subcontinent to produce extraordinary steel weaponry throughout the middle ages, known as Damascus steel.

Wootz (called hypereutectoid by modern metallurgists) is not specific to a particular outcrop of iron ore but is instead a manufactured product created by using a sealed, heated crucible to introduce high levels of carbon into any iron ore. The resulting carbon content for wootz is reported variously but falls between 1.3-2 percent of the total weight.

Why Wootz Steel is Famous

The term 'wootz' first appears in English in the late 18th century, by metallurgists who conducted the first experiments trying to break down its elemental nature. The word wootz may have been a mistranscription by scholar Helenus Scott of "utsa", the word for a fountain in Sanscrit; "ukku", the word for steel in the Indian language Kannada, and/or "uruku", to make molten in old Tamil. However, what wootz refers today is not what the 18th-century European metallurgists thought it was.

Wootz steel became known to Europeans in the early Medieval period when they visited Middle Eastern bazaars and found blacksmiths making amazing blades, axes, swords, and protective armor with gorgeous water-marked surfaces. These so-called "Damascus" steels may be named for the famous bazaar in Damascus or the damask-like pattern that was formed on the blade. The blades were hard, sharp, and able to bend up to a 90-degree angle without breaking, as the Crusaders found to their dismay.

But the Greeks and Romans were aware that the crucible process came from India. In the first century CE, the Roman scholar Pliny the Elder's Natural History mentions the importation of iron from Seres, which likely refers to the southern Indian kingdom of Cheras. The 1st century CE report called Periplus of the Erythraen Sea includes an explicit reference to iron and steel from India. In the 3rd century CE, the Greek alchemist Zosimos mentioned that the Indians made steel for high-quality swords by "melting" the steel.

Iron Production Process

There are three main types of pre-modern iron manufacture: bloomery, blast furnace, and crucible. Bloomery, first known in Europe about 900 BCE, involves heating iron ore with charcoal and then reducing it to form a solid product, called "a bloom" of iron and slag. Bloomery iron has a low carbon content (0.04 percent by weight) and it produces wrought iron. Blast furnace technology, invented in China in the 11th century CE, combines higher temperatures and a greater reduction process, resulting in cast iron, which has a 2–4 percent carbon content but is too brittle for blades.

With crucible iron, blacksmiths place pieces of bloomery iron along with carbon-rich material into crucibles. The crucibles are then sealed and heated over a period of days to temperatures between 1300–1400 degrees centigrade. In that process, the iron absorbs the carbon and is liquefied by it, allowing the complete separation of slag. The produced wootz cakes were then allowed to cool extremely slowly. Those cakes were then exported to arms manufacturers in the Middle East who carefully forged the fearsome Damascus steel blades, in a process which created the watered-silk or damask-like patterns.

Crucible steel, invented in the Indian subcontinent at least as early as 400 BCE, contains an intermediate level of carbon, 1–2 percent, and compared to the other products is an ultra-high carbon steel with high ductility for forging and high impact strength and reduced brittleness suitable for making blades.

Age of Wootz Steel

Iron making was part of Indian culture as early as 1100 BCE, at sites such as Hallur. The earliest evidence for the wootz type processing of iron includes the fragments of crucibles and metal particles identified at the 5th century BCE sites of Kodumanal and Mel-siruvalur, both in Tamil Nadu. Molecular investigation of an iron cake and tools from Junnar in Deccan province and dating to the Satavahana dynasty (350 BCE–136 CE) is clear evidence that crucible technology was widespread in India by this period.

The crucible steel artifacts found at Junnar were not swords or blades, but rather awls and chisels, tools for everyday working purposes such as rock carving and bead making. Such tools need to be strong without becoming brittle. The crucible steel process promotes those characteristics by attaining long-range structural homogeneity and inclusion-free conditions.

Some evidence suggests that the wootz process is older still. Sixteen hundred kilometers north of Junnar, at Taxila in present-day Pakistan, archaeologist John Marshall found three sword blades with 1.2–1.7 percent carbon steel, dated somewhere between the 5th century BCE and 1st century CE. An iron ring from a context at Kadebakele in Karnataka dated between 800–440 BCE has a composition close to .8 percent carbon and it may very well be crucible steel.

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