Iron Work and Santubong
The Santubong delta iron working industry began in 615 AD at the earliest and 900 AD at the latest and stopped around 1380 AD. They used a single Carbon 14 date and associated Chinese stoneware and coins and some religious artefacts of the Buddhists era to date the iron. Both of these early dates fit in nicely with the arrival of the first ruler in ~960 AD. The oral history we have collected says the first rulers came from Tanjungpura in the mid ~900 AD.
There were three major sites. These include the earliest, Sungei Jaong, with Sungai Buah coming next (which then silted up), followed by Bongkisam which ceased production in 1380. This last date seems to coincide with the lack of Ming Pottery from China which Harrisson called it the “Ming Gap”. It seems the lack of Ming pottery was caused the lack of iron.
The bog ore from which the iron was smelted was only 16% iron. This produced slag (left over waste) which was 66.7% iron (Fe0). The iron produced was 96.0% pure. The similarity of the slag from the three sites indicate a similar procedure was used.
Was the ore from Bau? The data indicates that there was not any indications of copper, antimony, arsenic or sulphur which is found in the Bau slag. However, the evidence was too slight to say it either was or was not from Bau.
How was the iron smelted?
A small clay pit is dug, 30 cm deep, 8 cm square at the bottom increasing to 23 cm at the top. This serves as the smelting furnace. Two large bamboo canes, about 1 meter long and 8 cm and 10 cm in diameter were used for cylinders. A smaller cane is inserted to the bottom to act as a tweer. These tweers are so placed as to admit a jet blast about six cm above the bottom of the pit. A bundle of feathers (to spread out the air from the tweers, I think) act as a piston.
The pit is half filled with wood charcoal on which is placed a certain quantity of iron ore. In about a half an hour the whole is fused. The slag is then allowed to run off and the metal is taken out to another similarly constructed furnace where the heating is repeated in order to refine the iron. Because of the silica found in the slag, the temperature must have reached 1150 C. The cooling of the slag must have quite slow because of the appearance of crystallized iron. If the iron had been quickly cooled these patterns would not have formed.
After this, the liquefied iron is poured on a stone. It is then shaped for parangs and for export. One to two kilograms of iron are required to make one parang.
One of the properties of this iron was the accidental addition of phosphorus to the iron. This addition, from the burning wood, produced an iron which was excellent in the making of weapons. This accidental addition made Sarawak iron in high demand. In an interesting quote by Burns,(I don’t know who he was as there is only a small reference in the bibliography) states the Kenya people could make iron of different hardness or softness by varying the type of wood used. This means they would have to know which wood contained high or low quantities of phosphorous when burned or which woods made different types of iron.
In the great debate about whether the articles found by Harrisson were either crucibles or nozzles, the authors state they were nozzles. They were probably used to conduct air onto the glowing coals to increase temperature.
We can state the accidental addition of Phosphorus to the iron from the burning coals made Sarawak Iron the very best for making parangs and swords.
Fr: Chemical Analysis of Iron, Iron Slag and Pottery Remains in the Prehistoric Iron Industry of the Sarawak River Delta. by F.E. Treloar Department of Physical Chemistry University of Melbourne in the Sarawak Museum Journal, December, 1975
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