Spelter statuary alloy?

Who knows anything about spelter alloy, as commonly used for cheap fake bronze statuary?
All I know is that it's either zinc or zinc-based alloy, and that it appeared in the later part of the 19th century when the price of zinc metal fell, owing to new smelting processes. It's cast at a lower temperature than bronze, making the moulds cheaper. When suitably patinated it also made an acceptable fake bronze for mass-produced indoor statuary.
Now there's another couple of well-known zinc alloys - Zamak/Mazak and their precursors. These were used for diecasting, most famously for diecast toys to replace lead. As is all too well known amongst collectors, the alloys before Zamak have a failure mode where they crack and distort after some years of age. This is caused by inter-granular precipitation of iron impurities in the zinc alloy. Zamak fixed this by being based on a very high purity zinc alloy, newly obtained from an improved smelting process with an extra reflux purification stage.
My question is this - If diecast zinc alloys of the early '30s don't survive, how does the older and presumably cruder spelter alloy manage? What's in it? How does it avoid these damaging impurities?

On Fri, 23 Dec 2005 13:13:05 +0000, Andy Dingley
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===============FWIW When i worked in the carburetor industry a major problem was the melting of reject die cast zinc components without removing the lead shot used to seal off drilled passages, for example where 2 drilled holes intersected to "turn a corner." Story was that even one piece of lead the size of a BB would cause the entire melt to age/stress crack in a few days to a few months. Several times I have been next to a cargotainer of these parts and have heard them crack.
Uncle George

On Fri, 23 Dec 2005 18:06:05 -0600, F. George McDuffee
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Lead is a worse impurity than iron in this respect, although when smelting it it's easier to reduce the impurity level. Given the purity standards that were needed (and were attained in the '30s) I can well believe your recycling story.
For some long recent period lead shot hasn't been used to seal passageways in diecastings (in UK practice at least). It's cheaper to use a more expensive hard brass plug and to use a four-point staking of the zinc onto the plug to seal it, rather than to risk having lead contamination show up from these conveninet soft lead plugs.

On Sat, 24 Dec 2005 00:23:37 +0000, Andy Dingley
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==============Yes -- my experience is from the late 60s in the US.
Most likely we would have been much better off using brass plugs. As you point out using lead shot was a carryover from the 1920s but so was the management. We still had one area where the cast iron bases for the carburetors were machined that had ovehead shafts and belt drive machinery. That department was a real coal mine. You could just walk past the door in a light colored shirt and it would show the soot.
Company is long out of business. Survived the great depression but could not withstand the MBA management. they milked the cash cow until she died.
Uncle George
Uncle George

On Fri, 23 Dec 2005 23:14:54 -0600, F. George McDuffee
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============More on the management problems --This should make more sense:
We had two groups of management. The production management were the hold overs from the 30/40s and resisted making any changes in products, methods, materials. The accounting and corporate management were all MBA whiz kids who would not allocate funds to update the products, methods, materials, etc. Between the two the squeezed every drop of blood out of the company. The only thing these two groups ever agreed on was "its the union's fault."
Uncle George

On Fri, 23 Dec 2005 23:14:54 -0600, F. George McDuffee
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I worked in the Austin Rover plant in the late '80s, early '90s. The A series lines (the Mini engine) were hacking away at a particularly Victorian grade of cast iron to machine the heads. Everything for 100 yards (including our electronics cabinets) was coated in a thick layer of black carbon dust from the cast iron. When Honda got involved (not before time) they erected a huge plywood partition wall between the old and the new (the Rover 400). Sadly the Mini, steam-driven pile of junk that it was, was the only car Rover marketing ever had a vague success with.