3rd Asia Pacific Precious Metals Conference on 09-11 June 2019 at PARKROYAL on Beach Road, Singapore..., Mark your dates for 16th India International Gold Convention on 01-04 Aug 2019 at Amritsar, Punjab...
 You are here : Home > Mining & Refining
 
 

Gold Refining Techniques Of A Medieval Islamic City Revealed By Experimental Archaeology

Tue June 18 2019

 

Archaeologists working at the medieval market city of Tadmekka recently discovered a set of ceramic molds used to cast metal coins. Tadmekka is located today in the country of Mali on the edges of the Saharan desert. During the Medieval period, the city’s strategic position made it a key player in the trade of ivory, textiles, glassware, and gold.

 

In his Book of Roads and Kingdoms Al-Bakri, an eleventh-century Arab historian, visited this critical trade outpost and noted something unusual about the gold coins being used in Tadmekka.  The dinars, or gold coins, were “bald.” That is to say, the coins had not been stamped with the identifying marks of a ruler or even of the city itself.

 

The lack of a stamp on these coins was deliberate. “At this time, the minting of coins was closely controlled by the Abbasid and Fatimid caliphates in the Middle East and North Africa, and Islamic rulers in West Africa did not possess independent authority to produce an inscribed coinage,” note Gianluca Pastorelli, Marc Walton, and Sam Nixon in their new joint research paper.  As a result, the discovery of coin molds at Tadmekka offers archaeologists a window into the informal economy of medieval Islamic empires.

 

Pastorelli, Walton, and Nixon’s work is part of a new museum exhibit, Caravans of Gold, Fragments in Time: Art, Culture, and Exchange across Medieval Saharan Africa, at The Block Art Museum of Northwestern University. The exhibit’s curator, Kathleen Bickford Berzock, notes that “the legacy of medieval trans-Saharan exchange has largely been omitted from Western historical narratives and art histories, and certainly from the way that Africa is presented in art museums.”

 

In the exhibit catalog, published by Princeton University Press, Pastorelli, Walton, and Nixon were able to come together and shine light on to an intriguing process by which the residents of Tadmekka were collecting low quality gold nuggets and purifying them to create high quality “bald” dinars.

 

Nixon has led the archaeological excavations at Tadmekka for more than ten years.  In addition to the coin molds, his excavations have also recovered a fragment of a ceramic crucible used to melt gold.  Such crucibles are rare in the archaeological record since they are usually broken to extract all possible traces of gold.  The recovered crucible fragment included an intriguing glassy substance that led Nixon and his colleagues to hypothesize that crushed glass had been used in the refining process.  Acting as a flux, glass was believed to remove oxide mineral particles from the gold resulting in higher levels of purity in the end product.

 

Indeed, scanning electron microscopy and particle-induced X-ray emission analyses of small fragments of gold found in the coin molds from Tadmekka demonstrated that the goldsmiths were working with gold that was 98% pure.  To test Nixon’s hypothesis, Bickford Berzock brought materials scientists Walton and Pastorelli on to the project. Together they conducted a series of experiments to see if they could refine gold following this model.

 

Walton and Pastorelli mixed gold dust with sand from nearby Lake Michigan to mimic the alluvial gold dust that West African minors would have extracted from streams and soils in the region.  They then added crushed soda glass to the mixture and fired the sample to 1000 °C for up to seven hours.  After this firing process the gold and glass had separated with the glass removing a majority of the added sand leaving behind a purified gold button at the bottom of the test crucibles.

 

This collaborative research between archaeology and materials sciences confirms that the medieval Islamic goldsmiths of Tadmekka had not only found a way to work around the authorities by issuing unmarked dinars, but that they had also discovered an ingenious way to make the most out the gold deposits available to them.

 

 

Source: https://www.forbes.com