Monsoon Steel

Sri Lanka
Archaeological survey and
excavation over a number of years
revealed a major industry (80+
sites) of the 7th and 11th centuries
AD, based on a wind-powered
linear furnace design
Reconstructed furnace from
archaeological evidence
Experimental smelts in 1994 and 2007
mid-smelt - 1994
towards end of smelt - 1994
Flow of air and flame up the front wall - 2007
Smelting at night
Smelting at night gave clues to the complex air flows
through and over the furnace
Breaking apart the
furnace and slag
to retrieve the
metal ‘blooms’
Metal products of smelts
Analysis showed this to be
high quality high-carbon steel
High-carbon steels and Damascus swords
At the time the wind-powered
furnaces of Sri Lanka were producing
high-carbon steel the Early Islamic
writer al-Kindi praised Sarandibi
steel as one of the most desirable
for sword-making
Data visualisation
Data sets
• wind direction and velocity for region and macro-environment
• wind direction and velocity for site-level environment
• wind velocities at furnace level during experimental smelting
• furnace temperatures at tuyere (air inlet) and charcoal bed during smelting
• ore and charcoal fuel charging weights and rates
• tap slag running times
The results of the field
experiments were published in
Nature (379, 1996)
Tangible and Intangible Archaeology
Collected hard evidence – slag waste,
metals, furnace remains, experimental
experience, images, data
How do we ‘capture’ the fugitive but
critical evidence of natural and
managed air flow and combustion?
How do we visualise it and importantly
use it as a tool for further research?
First interpretation of air flow through furnace based on
observations and recorded data (furnace cross-section)
Further research using computational
fluid dynamics (CFD) at Exeter refined
the initial analysis. Paper with Gavin Tabor
published in Journal of Archaeological Science
Arrangement of instruments to measure temperature
Computation of all temperature readings across furnace through duration of smelt (Matt Baker)
Further applications: other furnace technologies
Sri Lanka: small, bellows-driven shaft furnace
last used in early 20th century
Well-recorded example with archaeological,
ethnographic and documentary records
Furnace shape and size reconstructed from excavation and
written accounts
Experimental example built and run in Exeter by engineering
students (MJ Baker, R De Salis, D Dawson)
CFD analysis of airflows including quasi-sinusoidal flow