How were Chinese coins made?

[PeterD]

It's well known that Chinese coins were cast. The earlier one's were obviously just poured into a shallow mould (or "tree" of moulds) as the reverses are flat. The later ones, though, have a reverse which although usually have no lettering, have a rough surface and raised area around the rim and the square hole. Does anyone know how this was achieved?


Western Han  200-140 BC
Northern Ch'i 550-557 AD

[Manzikert]

Hi Peter

Basically, the early type single sided coins (eg pan liang) were cast in single sided clay or stone moulds, and had little treatment after being removed from the moulds.

The earlier double-sided coins (wu shu, etc) were cast from double sided clay moulds, and had little treatment other than the filing of the edges to remove the casting sprue and any 'flash'.

The later cast coins were cast from moulds made by pressing a number of 'mother' coins into sand moulds, then putting another layer of sand over the other side of the 'mother' coins, separating the two halves of the mould, removing the 'mother' coins and then placing the two halves of the moulds together again. The molten bronze would be poured into channels left in the mould by rods removed at the same time as the 'mother' coins, resulting in a 'tree' of rough coins. the individual coins are broken off the tree, and the raised parts of the faces of the coins polished by rubbing them back and forth over an abrasive surface or by filing the faces of the coins. Finally the coins are threaded onto a square metal rod and the edges of the coins are filed round.

The result is a coin with flat tops to the raised areas, and a grainy surface to the fields, the impression of the sand in the original mould.

That is a very basic explanation, but see http://www.history.ucsb.edu/faculty/roberts/coins/manufacture.html for an illustrated (Japanese) account of the later process.

Best wishes

Alan

[PeterD]

Thanks for your explanation, Alan.

What I don't quite understand is why the second layer of sand of wouldn't just stick to, or merge with the first layer. And how can the second layer of sand then be lifted up to remove the seed coins without it falling apart.

[Howard Cole]

Peter, I can not really answer your question, since I have never done any casting.  But I know that sand casting of three dimensional objects is still done today with modes that split in half.  I know that a special sand is used but don't know how it is prepared to keep its shape.

[Manzikert]

Hi Peter

As I understand it the Chinese used a thin layer of finely powdered charcoal on top of the first layer of sand (but not on the 'mother' coins) as a separator layer between the two halves of the final mould. These days things like lycopodium powder or finely powdered talc are used, but I suspect any very finely powdered dry substance might work just as well.

The secret of successful sand casting is in the preparation of the sand to be used (often it is mixed with a small amount of clay, but even oils and resins can be used) and the careful and uniform compaction of the sand both below and above the item being used to form the mould.

I suspect that with their long history of bronze casting the chinese knew all the secrets

Best wishes

Alan

[Robert_Brenchley]

It sounds like a slow and labour-intensive process. Who would have done the work, slaves? I know nothing of the history of the Chinese economy.

[Manzikert]

Hi Robert

Certainly not slaves from the 8th century at least: many of the descriptions of the process mention the wages of the workers as being part of the expense of casting. One account from 1741 even divides the workers into eight kinds who presumably got different wages, but unfortunately doesn't say what those wages were. In 1657 100 catties of copper (about 60 kilos) made 10,057 cash, and the costs (including wages) for this were 2,695 cash, so the government made a 75% profit.

In 1660 the two mints in the capital alone used 4,430,000 catties (c.2,658 tons) of copper to make about 445,500,000 cash: it may have been labour intensive, but I think the mints must have been a hive of activity during the casting periods. Practiced and skilled staff one has to assume.

Best wishes

Alan

[Robert_Brenchley]

Thanks. That points up some differences between China and Rome!

[Tantalus]

...That is a very basic explanation, but see http://www.history.ucsb.edu/faculty/roberts/coins/manufacture.html for an illustrated (Japanese) account of the later process.

Best wishes

Alan

Thanks for that link and the other information Alan. Very interesting.


Rodger

[samwyi]

Here are some mother coins from Qing Dynasty, they were normally carefully polished:







To compare with the seed coins, here are some regular commercial issues, which looks much cruder: