The Celtic mother-matrix from Bulgaria: http://balkancelts.wordpress.com/2012/07/28/the-mother-matrix/
Just to clarify the technical aspects of this unique object. According to further research, this is not a master die, but a 'mother coin'. A master die is used for making working dies and working dies are used for striking coins. If the product you make is made of clay, it would not survive a single strike, so this object is not used for striking coins. Instead, it is used as a mother coin for casting coins and indeed, you can make a virtually unlimited number of them. Casting is an ancient technique, used later both in East Asia and in the Roman empire. It produces perfectly usable coins, but with more time, more effort and the coins are more brittle. A 'mother coin' is used to impress the picture a number of times in a clay tablet. A mother coin for the other side is used on another tablet. The impressions are connected by a casting canal, leading to a central casting canal. The two tablets are dried or fired and put together, forming a casting mould, which is carefully filled with molten metal. When the metal is solidified, the mould is broken, the coins are broken from the casting canals and filed to the correct weight. Where this mother coin becomes amazing is that Roman moulds we know were made of stone. The coins were cut directly into the stone, without a mother coin and the stone would obviously not be destroyed after casting. The Celts must have used a softer material, or they wouldn't have made the mother coin. Therefore, it is quite possible that they were using clay, like the Chinese, rather than stone like the Romans. So it appears that the Celtic technology was more similar to the Chinese than the Romans.... (For this info. thanks to Peter at Worldofcoins.eu)
