A question from the past 上市 Deposited
Cast Coins
- From jlorenzo@ob.ilww.com Fri May 24 09:46:58 2002
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Date: Fri, 24 May 2002 16:46:37 -0000
To: colonial-coins@yahoogroups.com
Subject: Cast Coins: A question from the past
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From: "njcopperjohn" <jlorenzo@ob.ilww.com>
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Let me say before I start this post that no numismatic paper has
affected me more in terms of numismatic importance than the paper
that Charles Smith and Phil Mossman did in April,1998. When I read
this paper I really did agree with every statement but one back in
April, 1998 when it was published. I suspect the authors knew a
little more than they printed but having dealt with Phil before I
know that he at times can be a conservative writer and wants to be
absolutely certain that information that he publishes is very
accurate with not much chance for error. This is good. I should learn
to be a little more like this individual. Having said all this Phil
and since we are starting again on this metallurgical attribution
pathway again the line which I was uncomfortable with was on page
1783 of CNL Vol.38, No.1 which reads:
The major constituent was always copper, in order to yield the
expected look, but beyond that, the soupe-du-jour was poured into the
mouth of the coin mold.
I disagree 100% with this statement Phil and here are my reasons:
1.Lead is frequently added to copper alloys to increase their
machinability today. The role of lead back then was for this reason
but in copper alloys to the counterfeiter it was two-fold, to act as
a lubricant and for easier release from the mold of the finished
copper alloy cast coin once the process was over.
2.Copper tin alloys or tin bronzes are known for their corrosion
resistance. Tin also adds ductility and greater wear resistance to
the finished copper alloy composition. Tin is not a accidental
addition in this mix.
3. One major differentiation on the study coins was specimen #19 the
high zinc piece this counterfeiter simply used brass as its base
alloy for this cast composition.
4. Zinc alloying with copper to give brass accounts for its
appearance 'at times' in your results.
5. If I was to make the perfect copper cast alloy composition product
it would be unquestionably a copper/tin/lead composition.
Quantitative varaition of tin and lead is simply there with the base
copper because its 1750.
6. These cast coins are not in my opinion haphazard mixtures but very
accurately pre-determined alloy compositions.
7. The metal iron is a contaminant of the manufacturing process in my
opinion as iron from my studies has no value in a copper alloy make-
up. Agree???
8. Further, lead is practically insoluble in solid copper and it
solidifies last in the cooling process in the mold it forms as pure
lead in the grain broundaries of the cast coin. Lead values on the
interior of these cast coins will be lower and the amounts of lead in
the original mix must also be lower is an important consideration in
future studies. Agree?
9. It seems the American made? casts follow this same generic formula
of Copper/Lead/Tin with some contaminants again as expected
infrequently showing up and being reported. Agree?
Phil -just thought I bring the metal analysis discussions up a notch.
Respectively Submitted
John Lorenzo. - 2002-05-24
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