Some people believe every single word of Plato's account to be true, while other people believe every single word to be totally false. Yet there are small details, like the mysterious alloy called "Orichalcum" which one translator, Sir Desmond Lee considered to be "a completely imaginary metal" but actually exists in the Andes as an alloy of gold and copper. Here is what Karen Olsen Bruhhs writing in "Ancient South America" has to say about it... "Copper and copper alloy objects were routinely gilded or silvered, the original colour apparently not being much valued. The gilded copper objects were often made of an alloy which came to be very important in all of South and Central American metallurgy: tumbaga. This is a gold-copper alloy which is significantly harder than copper, but which retains its flexibility when hammered. It is thus ideally suited to the formation of elaborate objects made of hammered sheet metal. In addition, it casts well and melts at a lower temperature than copper, always a consideration when fuel sources for a draught were the wind and men's lungs. The alloy could be made to look like pure gold by treatment of the finished face with an acid solution to dissolve the copper, and then by hammering or polishing to join the gold, giving a uniformly gold surface."

An axe head from Tiwanaku, Bolivia.
Made of "orichalcum" – a mixture of gold and copper with a small percentage of arsenic
- the untreated surface is darkened with copper oxide

The process was further explained and demonstrated by Adam Hart-Davis in his programme "What The Ancients Did For Us" screened by the "Open University" (BBC2) 2nd March 2005. Since gold was not used as a currency, it was valued more for its colour and beauty, gold being the "sweat of the sun" and silver being the "tears of the moon." Taking a small piece of Tumbaga consisting of 50% gold and 50% copper, the alloy was hammered into the shape of a miniature mask suitable for mounting on a finger ring.

  a small block of orichalcum before working       the metal is punched into the shape of a mask

At this stage it looked like polished copper before being annealed by heating with a torch to a cherry-red colour at a temperature of 500º.

the untreated alloy of orichalcum      heated until it turns cherry-red

The alloy was then quenched in water whereby it turned black due to the copper on the surface oxidising and turning into copper oxide on top of the gold.

quenched in water it turns black due to the copper oxide
the copper oxide is dissolved in a solution of alum

The alloy was then immersed in a hot solution of Alum whereupon like some ancient alchemical process, the copper oxide dissolved away revealing a shining gold surface of quote "the most noble of the metals looking like pure gold."

left, the alum dissolves away the copper oxide to reveal a gold-like object
right, Orichalcum after the copper has been dissolved from the surface