East Asian coining technology

Started by bgriff99, September 29, 2014, 03:25:38 AM

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bgriff99

Baked clay molds are an exception.   It's slow.   It was the ancestral method of bronze and iron implement casting developed to a science already by 1400BC.   To mass produce metal articles molds were made stackable, fired in room-sized kilns, then used for casting in the position they were fired in.   China was using cast iron more than 2000 years before Europe.    But making pieces by the hundred, not millions.

Coin casting went through a sequence of systems starting with uniface open molds of clay or soft stone.   At the height of mold technology they were actually themselves of bronze, large and elaborate.   Their sections were cast in fine stoneware molds.    I'd have to check to be sure, but that period was in circa 100BC to 600 AD.   I don't know why that was abandoned.

The norm is "sand cast", which actually uses crushed heat-dried pulverized clay mixed with other proprietary ingredients like dried crushed brick, wood ash, fumed tree resin and so forth.   (I suspect it evolved from attempts to reuse fired mold clay from baked molds.)   It was pressed into wooden trays about an inch deep.   It had to be cohesive enough to remain in place held with the rack on its side (its position as metal was poured) and even upside down as they were turned over.   Its working surface was dusted with powdered charcoal flux.    A single loading of mother cash and channel bars would be repeatedly transferred in position from tray to tray in a flip-over sequence that could be done quickly by experienced workmen.   Then ten or so trays would be bound into a bundle for casting.   The same set of mother cash could make bundle after bundle until enough were prepared to receive one crucible of metal.    Most Sung, Ming and Ching cash are sand-cast.

I made a miniature one-coin tray to try making cash.   I succeeded in making some horrible looking ones out of zinc and lead.   I did a lot of sinker, bullet and shot casting when I was a kid in homemade molds, and later musket and pistol bullets in regular steel molds.   Coin casting is a whole other thing.    I reiterated the experience of the Beijing mints attempting to cast with zinc in 1853 or so.   It kept catching on fire.  Adding some lead stops that.   But the Nguyen coins which have been tested are at 99% zinc.    Which also backs up the documentation saying it came from China.    Another interesting junk box coin I found circa 1974 is one of those zinc-lead cash, grayish black, which I picked out thinking it was iron.   The zinc-lead coins at that time were not even listed in catalogs!

When removed from the mold in the form of a tree, individual cash were broken off and pushed onto a square iron rod about a foot long, for edge filing.   A taper at one end allowed the rod to act as a file for center flash.   Sung rosette hole cash are those jammed on each end so as to clamp them tightly while the edges were filed.   From about 1650 Vietnamese cash are usually found to have flash and sprue removed with a cookie cutter tool punched over the obverse.   Some cash appear to have gotten a considerable amount of individual face milling.   Most are just polished in bins shaken back and forth first with fine abrasive, then an oiled material like wheat chaff.   

Vietnamese cash of the Le dynasty 1428-1523, and the Mac 1527-46 appear to have reverted to baked clay molds.  That's just my opinion.   They may have been done that way all along.   Those coming by the 1700's are definitely sand cast.  Something of more interest on cash of more recent centuries is how the mother cash were made.   By direct engraving, or casting, or alteration of existing coins.   There is a short period (1713-22) when it looks like the Beijing mints hammered them into dies.   That reflects considerably on trying to work out dates.   Tin cash from the Malay peninsula and Sumatra are often found to be die-struck on cast flans.   Also sometimes from wooden molds.

These details just begin to touch on the complexity, expense and capital burden to make decent cash, which then had to circulate at about their intrinsic value.   It says nothing of the mining of the several metals needed, smelting and refining, transport and alloy composition, or the perpetual problems of inflation, debasement, counterfeits, export or prohibition thereof, different values, sizes or availability by region, etc.    This is something collectors virtually ignore in talking about them as if they were just popped out, permanently standardized, automatically and easily, with "varieties" being some mystery which however is not worth delving into.

My interest in them was drawn by the fact they were nowhere near fully cataloged.   There was and still is much to learn.    Meanwhile what is already known is poorly distributed, sometimes erroneous, subsequently becomes forgotten, and divided into multiple languages where there is almost no cross-reading.     Chinese numismatics and then Vietnamese took off in a roar shortly after the death of Mao.   Until then, official disdain of having enthusiasm for anything imperial had suppressed it.   For a while it was the all-time golden era for us to acquire Chinese cash, in particular from Indonesia and Sinkiang.   For study, if wanted, cheaply by the thousand.   Right now is still a great time to acquire Vietnamese coins.