Intangible archaeologies of hot air MONSOON STEEL Intangible archaeologies of hot air

Sri Lanka

Samanalawewa

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

Tangible and Intangible Archaeology 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 model

POTENTIAL With good datasets from archaeological excavations and experimental smelting Visualise and model CFD data Potential as a tool for study and interpretation of ancient pyrotechnologies Potential to make visible intangible archaeology Potential for interdisciplinary knowledge transfer and public dissemination Potential to engage with creative industry to present science and technology THANK YOU