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  #61   Report Post  
Old June 29th 04, 12:13 AM
Tom McDonald
 
Posts: n/a
Default Copper Casting In America (Trevelyan)

Eric Stevens wrote:

On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman
wrote:


snip

Now
of course the Old Worlders had the advantage of ores which
did contain suitable deoxidizers. They weren't actually casting
pure copper. But the Michigan copper was essentially pure
native copper.


But it wasn't the only source of copper.


Eric,

This thread began, and has mostly developed, around that
Michigan (with some from Wisconsin and Minnesota) native copper,
more specifically its use in the upper Great Lakes area.

Yuri has begun a thread about copper casting outside of this
area. Perhaps that would be a better venue for this more
general discussion of ancient copper.

Tom McDonald

  #62   Report Post  
Old June 29th 04, 03:42 AM
Paul K. Dickman
 
Posts: n/a
Default Copper Casting In America (Trevelyan)


Tom McDonald wrote in message ...
Eric,

In the context of this thread, at least its original context,
the copper was native copper in the upper Great Lakes area of
the US and Canada. That copper is typically well over 99% pure
out of the ground, and does not have to be smelted to remove
impurities. If another context is in evidence, then a
definition of the term 'pure' is needed.

In the cases Yuri noted (e.g.: Egypt, Harrapa, China), that
copper was apparently smelted from ore, and analysis of
individual artifacts would be necessary to describe the ratio of
copper to alloy materials. In one of Yuri's examples, 'pure'
copper artifacts were all below 98.8% copper.

I agree, therefore, that one cannot take a statement that some
artifact or artifact type was 'pure copper' at face value. It
needs to be quantified.

Tom McDonald




Much has been bandied about concerning the purity of the copper from the UP,
but you must realize that the same geological process that separates the
copper also separates several other metals at the same time. It does not
place them miles apart but leaves the next to each other, fractions of a
millimeter apart.
for some clarification we will define some vocabulary.

Native copper
This is copper that was left in it's metallic state by the process that
concentrated it. It can be loose, or they can be stuck in a hunk of matrix
exactly as they came out of the ground with other native metals in close
proximity.
Drift copper
This is native copper that has been pounded from its matrix by glacial
action.
Placer deposit
This is a deposit of native metal that has been removed from it's matrix
by erosion (glacial or otherwise) moved from it's original location (usually
by wind or water) and, by nature of its specific gravity and it's resistance
to the motive force has been concentrate with other bits of metal with like
characteristics.

The native copper of the UP is unusually pure. This does not, however, mean
that every piece of rock with copper in it contains only copper.

Below is snip from a site about gold mining in the UP.

..http://www.geo.msu.edu/geo333/gold.html


In June the following year(1846), Houghton’s younger brother Jacob, found a
vein of native copper on the Keweenaw Peninsula which held a small amount of
gold. An assay yielded 10.25 ounces of copper, 1.75 ounces of silver and 12
grains of gold from the 28-ounce specimen



You can see that this particular sample was nearly 15% silver!

Drift copper has had most of the other materials removed by mechanical
action and is usually very pure.

The specific gravities of silver, copper etc. are actually quite close when
compared to sand and placer deposits may contain these in any mix.

Now as to melting.

These native metals are melted for one of three basic reasons.

One, to change it's shape to a finished product
Even today, casting generally produces products that are inferior to
wrought. It is only used when the form cannot economically be produced any
other way,
It is fairly difficult with pure copper, and frankly, if you found a 3
lb hunk of drift copper you would be better off pounding it to shape.

Two, to amalgamate several smaller pieces into one or more larger ones.
The purpose of this is not ,necessarily, to produce a finished product,
but to produce an ingot . Despite copper's casting difficulties, we have
managed to pour ingots of it for almost as long as we have worked metals.
The beauty of the ingot is that if you make it big enough, you can cut
off the bad parts, melt them into the next ingot and pound the rest into
whatever you want.
However, since parent metal is no longer a single nugget of pure copper,
the purity of the casting can be anything.

Three, to separate the metals from the matrix.
This too produces a fine ingot and in the case of Mr. Houghton's sample,
one with 15% silver .


Paul K. DIckman



  #63   Report Post  
Old June 29th 04, 03:45 AM
Gary Coffman
 
Posts: n/a
Default Copper Casting In America (Trevelyan)

On Tue, 29 Jun 2004 09:49:39 +1200, Eric Stevens wrote:
On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman
wrote:
On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman
wrote:
No trick to melting copper. Doing something intelligent with the molten
metal in an atmospheric environment is a different matter. As I noted
previously, casting pure copper is difficult, even today.

But the question is, how pure was the copper.


The native copper we've been discussing is very high purity.
The halfbreed ore does contain silver, but the silver isn't in
solid solution with the copper (copper-silver alloys are difficult
to produce). Instead it is in the form of distinct crystal inclusions
which would melt out and separate before the copper would melt.

In any case, copper can mostly by prevented from oxidising by melting
it under a layer of crushed coal or charcoal. In fact this method was
used for the production of largely deoxised (tough-pitch) copper in
recent time.


A graphite cover was used to prevent oxidation while melting (coal
won't work because of the large fraction of volatiles, charcoal might
be useable). But you also have to deal with the air entrained when
pouring.


Here is a quote from 'Metallurgy for Engineers' Rollason, 2nd Edition,
first published 1939:

Begin quote:
---------------------------------
Production of Tough Pitch Copper. In fire-refining copper the
impurities are removed by oxidising the metal until about 4 per cent
copper oxide (Cu20) is absorbed. During this stage the impurities form
oxides more readily than the copper and are removed as a slag or
evolved as gas. The last impurity so removed is sulphur which is not
completely driven off as sulphur dioxide by mere oxidation, but to
remove the last traces the metal has to be violently agitated by
poling, i.e. introducing an unseasoned piece of wood under the
surface. This causes a miniature fountain of molten copper, and allows
the air to come into contact with the spraying metal. Small test
castings or button castings are taken to indicate the state of the
metal. With sulphur present the ingot spurts just as it goes solid due
to the evolution of gas (SO2), but as the sulphur is reduced in amount
the surface of the ingot sinks in the manner normal to most metals. If
a micro-examination is made of this metal it will be found to contain
globules of copper oxide in the form of a eutectic (Cu-Cu2O). A layer
of crushed coal is then placed on the molten copper, and as poling
continues the copper oxide is reduced and when a content of about 0.04
to 0.08 per cent oxygen is reached the surface of the button remains
level and the properties of the metal are good, in other words
"tough." The lower the oxygen, the higher the so-called "pitch" and
vice versa, hence the name "Tough Pitch." As poling continues past
this point the copper absorbs hydrogen from the furnace gases and when
cast the metal rises on solidification.
These changes in behaviour, micro-structure and mechanical properties
are due to the influence of hydrogen and oxygen on the copper.
----------------------------------------
End quote

The above confirms not only the use of crushed coal but also the
primitive nature of the processes by means of which relatively pure
copper was produced even in the 20th century. Stirring with a piece of
unseasoned wood is a practice which may have roots going back for
millenia.


The quote is a procedure for smelting chalcopyrite ore. That's a very
different procedure from what is required to process pure native copper.
Apples and oranges.

A bottom pour furnace is helpful, but you really need deoxidizers in
the alloy to prevent severe porosity problems. Tin and zinc are the
preferred deoxidizers. Arsenic also works, but the fumes are deadly.
Lead makes the metal more fluid, and assists in filling out the mold.
None of those are naturally present in the native copper we're
discussing.

Also, as a side note, where is the evidence for coal mining or large
scale charcoal production in the area? You don't get to copper
melting temperatures with a simple wood fire. You need a forced
draft fire with a high carbon fuel.


A good bed of well ventilated charcoal will suffice. One often finds
melted copper in the remains of burned out buildings.


A fully engulfed large building, or a forest fire, can produce sufficient
natural draft to reach copper melting temperature, but you'd need a
forced draft for a simple bed of charcoal. For doing very small amounts
of metal, such as small silver jewelry items, blowpipes would suffice, but
for doing anything on the order of the size of the artifacts we've been
examining, a bellows or blower would be required, and a *lot* of charcoal.

Let me propose that you conduct an experiment. Go to your local "high
end" audio shop and purchase some oxygen free copper "monster" wire
(similar properties to native copper). Now try to melt it in your backyard
barbeque. The insulation will burn off, but I'll be very surprised if you can
get the wire to melt without a forced air draft and *several* loads of
charcoal.

Making charcoal is an industrial enterprise in itself. I'm asking is there
any evidence of such activity in the area under discussion? So far I
have seen no reference to such activities. Nor have I seen any reference
to coal mining activity in the area. All that has been reported is mining
of native copper deposits.

I believe we are agreed that only atmospheric casting was within
reach of the ancient Native Americans (or ancient Old World
founders for that matter), so we *should* see characteristic
porosity in any pure copper items they attempted to cast.


Only if they used the relatively pure meteoric copper of Michigan. It
was laikely to be naturally alloyed if it was smelted.


Meteoric copper? Perhaps you're thinking of iron. The copper we're
discussing is native copper. Native copper is the result of a natural
geochemical leaching process in certain types of rock formations.
It results in extremely high purity copper.

Now
of course the Old Worlders had the advantage of ores which
did contain suitable deoxidizers. They weren't actually casting
pure copper. But the Michigan copper was essentially pure
native copper.

But it wasn't the only source of copper.


True, there are impure ores present in the region as well. But
there is absolutely no evidence that any of it was mined or
processed prior to the latter part of the 19th century. Further,
the impure ores which are present contain iron and sulphur
as their major contaminants. Those impurities are extremely
undesireable in copper that is to be cast. The ore has to be
smelted to remove those impurities.

No significant amounts of tin, zinc, arsenic, or lead, which
would improve casting qualities, are present in the ores of
the region. So even if the ancients had adulterated their
native copper with these ores, the result would not be an
improvement in the ability to cast objects from the resultant
mixture.

The ancients lacked a scientific understanding of metallurgy,
but they weren't stupid. They proceded by a sequence of trial
and error steps. If they added something, and the result was
worse, they'd quickly understand not to do that again. Since
the Native Americans in Michigan already had access to very
high purity native copper, and any local adulterant they added
would only make its properties worse, I'd suggest that they
quickly learned not to add any adulterants.

Now the situation was different in the Old World. The metalworkers
there had access to adulterants which *would* improve the casting
properties of copper, and they fairly quickly learned to add such
materials to their copper. That's not because they were brighter,
it is simply because they had materials at hand which weren't
available to the ancients of Michigan.

Gary
  #64   Report Post  
Old June 29th 04, 04:31 AM
Tom McDonald
 
Posts: n/a
Default Copper Casting In America (Trevelyan)

Paul K. Dickman wrote:

Tom McDonald wrote in message ...

Eric,

In the context of this thread, at least its original context,
the copper was native copper in the upper Great Lakes area of
the US and Canada. That copper is typically well over 99% pure
out of the ground, and does not have to be smelted to remove
impurities. If another context is in evidence, then a
definition of the term 'pure' is needed.

In the cases Yuri noted (e.g.: Egypt, Harrapa, China), that
copper was apparently smelted from ore, and analysis of
individual artifacts would be necessary to describe the ratio of
copper to alloy materials. In one of Yuri's examples, 'pure'
copper artifacts were all below 98.8% copper.

I agree, therefore, that one cannot take a statement that some
artifact or artifact type was 'pure copper' at face value. It
needs to be quantified.

Tom McDonald





Much has been bandied about concerning the purity of the copper from the UP,
but you must realize that the same geological process that separates the
copper also separates several other metals at the same time. It does not
place them miles apart but leaves the next to each other, fractions of a
millimeter apart.
for some clarification we will define some vocabulary.

Native copper
This is copper that was left in it's metallic state by the process that
concentrated it. It can be loose, or they can be stuck in a hunk of matrix
exactly as they came out of the ground with other native metals in close
proximity.
Drift copper
This is native copper that has been pounded from its matrix by glacial
action.
Placer deposit
This is a deposit of native metal that has been removed from it's matrix
by erosion (glacial or otherwise) moved from it's original location (usually
by wind or water) and, by nature of its specific gravity and it's resistance
to the motive force has been concentrate with other bits of metal with like
characteristics.

The native copper of the UP is unusually pure. This does not, however, mean
that every piece of rock with copper in it contains only copper.

Below is snip from a site about gold mining in the UP.

.http://www.geo.msu.edu/geo333/gold.html


In June the following year(1846), Houghton’s younger brother Jacob, found a
vein of native copper on the Keweenaw Peninsula which held a small amount of
gold. An assay yielded 10.25 ounces of copper, 1.75 ounces of silver and 12
grains of gold from the 28-ounce specimen



You can see that this particular sample was nearly 15% silver!

Drift copper has had most of the other materials removed by mechanical
action and is usually very pure.

The specific gravities of silver, copper etc. are actually quite close when
compared to sand and placer deposits may contain these in any mix.

Now as to melting.

These native metals are melted for one of three basic reasons.

One, to change it's shape to a finished product
Even today, casting generally produces products that are inferior to
wrought. It is only used when the form cannot economically be produced any
other way,
It is fairly difficult with pure copper, and frankly, if you found a 3
lb hunk of drift copper you would be better off pounding it to shape.

Two, to amalgamate several smaller pieces into one or more larger ones.
The purpose of this is not ,necessarily, to produce a finished product,
but to produce an ingot . Despite copper's casting difficulties, we have
managed to pour ingots of it for almost as long as we have worked metals.
The beauty of the ingot is that if you make it big enough, you can cut
off the bad parts, melt them into the next ingot and pound the rest into
whatever you want.
However, since parent metal is no longer a single nugget of pure copper,
the purity of the casting can be anything.

Three, to separate the metals from the matrix.
This too produces a fine ingot and in the case of Mr. Houghton's sample,
one with 15% silver .


Paul K. DIckman


Paul,

I'm getting a good free education in this copper business. I
thank you and Gary for your tutelage.

I don't recall reading anything about, for instance, silver
artifacts in the upper Great Lakes area; but this doesn't mean
it wasn't used. I rather suspect that folks were breaking rocks
to extract copper, and may have discarded as debitage the
non-copper bits.

I'll have to look into this, as it would seem that silver might
have been present in large enough amounts that it might have
wound up in archaeological contexts. And, of course, when white
folks came later to investigate and further exploit some of the
copper deposits, I'd be surprised if any silver were to have
been ignored by them.

Tom McDonald
  #65   Report Post  
Old June 29th 04, 04:40 AM
Eric Stevens
 
Posts: n/a
Default Copper Casting In America (Trevelyan)

On Mon, 28 Jun 2004 21:45:11 -0400, Gary Coffman
wrote:

On Tue, 29 Jun 2004 09:49:39 +1200, Eric Stevens wrote:
On Mon, 28 Jun 2004 13:07:35 -0400, Gary Coffman
wrote:
On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman
wrote:
No trick to melting copper. Doing something intelligent with the molten
metal in an atmospheric environment is a different matter. As I noted
previously, casting pure copper is difficult, even today.

But the question is, how pure was the copper.

The native copper we've been discussing is very high purity.
The halfbreed ore does contain silver, but the silver isn't in
solid solution with the copper (copper-silver alloys are difficult
to produce). Instead it is in the form of distinct crystal inclusions
which would melt out and separate before the copper would melt.

In any case, copper can mostly by prevented from oxidising by melting
it under a layer of crushed coal or charcoal. In fact this method was
used for the production of largely deoxised (tough-pitch) copper in
recent time.

A graphite cover was used to prevent oxidation while melting (coal
won't work because of the large fraction of volatiles, charcoal might
be useable). But you also have to deal with the air entrained when
pouring.


Here is a quote from 'Metallurgy for Engineers' Rollason, 2nd Edition,
first published 1939:

Begin quote:
---------------------------------
Production of Tough Pitch Copper. In fire-refining copper the
impurities are removed by oxidising the metal until about 4 per cent
copper oxide (Cu20) is absorbed. During this stage the impurities form
oxides more readily than the copper and are removed as a slag or
evolved as gas. The last impurity so removed is sulphur which is not
completely driven off as sulphur dioxide by mere oxidation, but to
remove the last traces the metal has to be violently agitated by
poling, i.e. introducing an unseasoned piece of wood under the
surface. This causes a miniature fountain of molten copper, and allows
the air to come into contact with the spraying metal. Small test
castings or button castings are taken to indicate the state of the
metal. With sulphur present the ingot spurts just as it goes solid due
to the evolution of gas (SO2), but as the sulphur is reduced in amount
the surface of the ingot sinks in the manner normal to most metals. If
a micro-examination is made of this metal it will be found to contain
globules of copper oxide in the form of a eutectic (Cu-Cu2O). A layer
of crushed coal is then placed on the molten copper, and as poling
continues the copper oxide is reduced and when a content of about 0.04
to 0.08 per cent oxygen is reached the surface of the button remains
level and the properties of the metal are good, in other words
"tough." The lower the oxygen, the higher the so-called "pitch" and
vice versa, hence the name "Tough Pitch." As poling continues past
this point the copper absorbs hydrogen from the furnace gases and when
cast the metal rises on solidification.
These changes in behaviour, micro-structure and mechanical properties
are due to the influence of hydrogen and oxygen on the copper.
----------------------------------------
End quote

The above confirms not only the use of crushed coal but also the
primitive nature of the processes by means of which relatively pure
copper was produced even in the 20th century. Stirring with a piece of
unseasoned wood is a practice which may have roots going back for
millenia.


The quote is a procedure for smelting chalcopyrite ore.


I don't know where you get that from. The opening sentence says very
clearly "In fire-refining copper ... ".

That's a very
different procedure from what is required to process pure native copper.
Apples and oranges.


But then that's not why I quoted the article. I did so to deal with
your rebuttal of the use of a layer of coal to prevent oxidisation.

A bottom pour furnace is helpful, but you really need deoxidizers in
the alloy to prevent severe porosity problems. Tin and zinc are the
preferred deoxidizers. Arsenic also works, but the fumes are deadly.
Lead makes the metal more fluid, and assists in filling out the mold.
None of those are naturally present in the native copper we're
discussing.

Also, as a side note, where is the evidence for coal mining or large
scale charcoal production in the area? You don't get to copper
melting temperatures with a simple wood fire. You need a forced
draft fire with a high carbon fuel.


A good bed of well ventilated charcoal will suffice. One often finds
melted copper in the remains of burned out buildings.


A fully engulfed large building, or a forest fire, can produce sufficient
natural draft to reach copper melting temperature, but you'd need a
forced draft for a simple bed of charcoal. For doing very small amounts
of metal, such as small silver jewelry items, blowpipes would suffice, but
for doing anything on the order of the size of the artifacts we've been
examining, a bellows or blower would be required, and a *lot* of charcoal.

Let me propose that you conduct an experiment. Go to your local "high
end" audio shop and purchase some oxygen free copper "monster" wire
(similar properties to native copper). Now try to melt it in your backyard
barbeque. The insulation will burn off, but I'll be very surprised if you can
get the wire to melt without a forced air draft and *several* loads of
charcoal.


Actually I have carried out that very experiment to replicate damage
seen to 'Monster cable' in a domestic fire. Just for the heck of it I
through some into the base of a Jotul Alpha wood stove. The monster
cable variously melted or sintered into a solid bar of copper. FYI,
the Jotul Alpha is an 'air-tight' stove with the only air entry being
down the face of the front door glass from the top.

Making charcoal is an industrial enterprise in itself. I'm asking is there
any evidence of such activity in the area under discussion? So far I
have seen no reference to such activities. Nor have I seen any reference
to coal mining activity in the area. All that has been reported is mining
of native copper deposits.


That's a very different question from the use of coal to prevent
oxidisation.

I believe we are agreed that only atmospheric casting was within
reach of the ancient Native Americans (or ancient Old World
founders for that matter), so we *should* see characteristic
porosity in any pure copper items they attempted to cast.


Only if they used the relatively pure meteoric copper of Michigan. It
was laikely to be naturally alloyed if it was smelted.


Meteoric copper? Perhaps you're thinking of iron.


Its a term used to describe the copper deposited by contact with
meteoric water. Meteoric water is ground water formed by
precipitation. See
http://www.minsocam.org/MSA/collecto...r/vft/mi2c.htm

The copper we're
discussing is native copper. Native copper is the result of a natural
geochemical leaching process in certain types of rock formations.
It results in extremely high purity copper.


Only in some places.

Now
of course the Old Worlders had the advantage of ores which
did contain suitable deoxidizers. They weren't actually casting
pure copper. But the Michigan copper was essentially pure
native copper.

But it wasn't the only source of copper.


True, there are impure ores present in the region as well. But
there is absolutely no evidence that any of it was mined or
processed prior to the latter part of the 19th century. Further,
the impure ores which are present contain iron and sulphur
as their major contaminants. Those impurities are extremely
undesireable in copper that is to be cast. The ore has to be
smelted to remove those impurities.

No significant amounts of tin, zinc, arsenic, or lead, which
would improve casting qualities, are present in the ores of
the region. So even if the ancients had adulterated their
native copper with these ores, the result would not be an
improvement in the ability to cast objects from the resultant
mixture.

The ancients lacked a scientific understanding of metallurgy,
but they weren't stupid. They proceded by a sequence of trial
and error steps. If they added something, and the result was
worse, they'd quickly understand not to do that again. Since
the Native Americans in Michigan already had access to very
high purity native copper, and any local adulterant they added
would only make its properties worse, I'd suggest that they
quickly learned not to add any adulterants.

Now the situation was different in the Old World. The metalworkers
there had access to adulterants which *would* improve the casting
properties of copper, and they fairly quickly learned to add such
materials to their copper. That's not because they were brighter,
it is simply because they had materials at hand which weren't
available to the ancients of Michigan.

Gary





Eric Stevens



  #66   Report Post  
Old June 29th 04, 07:48 AM
Seppo Renfors
 
Posts: n/a
Default Copper Casting In America (Trevelyan)



Gary Coffman wrote:

On Mon, 28 Jun 2004 08:52:10 +1200, Eric Stevens wrote:
On Sun, 27 Jun 2004 02:58:26 -0400, Gary Coffman
wrote:
No trick to melting copper. Doing something intelligent with the molten
metal in an atmospheric environment is a different matter. As I noted
previously, casting pure copper is difficult, even today.


But the question is, how pure was the copper.


The native copper we've been discussing is very high purity.
The halfbreed ore does contain silver, but the silver isn't in
solid solution with the copper (copper-silver alloys are difficult
to produce). Instead it is in the form of distinct crystal inclusions
which would melt out and separate before the copper would melt.

In any case, copper can mostly by prevented from oxidising by melting
it under a layer of crushed coal or charcoal. In fact this method was
used for the production of largely deoxised (tough-pitch) copper in
recent time.


A graphite cover was used to prevent oxidation while melting (coal
won't work because of the large fraction of volatiles, charcoal might
be useable). But you also have to deal with the air entrained when
pouring.

A bottom pour furnace is helpful, but you really need deoxidizers in
the alloy to prevent severe porosity problems. Tin and zinc are the
preferred deoxidizers. Arsenic also works, but the fumes are deadly.
Lead makes the metal more fluid, and assists in filling out the mold.
None of those are naturally present in the native copper we're
discussing.

Also, as a side note, where is the evidence for coal mining or large
scale charcoal production in the area? You don't get to copper
melting temperatures with a simple wood fire. You need a forced
draft fire with a high carbon fuel.

For a people
without inert gas shielded continuous casting furnaces, it would be
nothing but frustration.


Don't under rate the cunning of anceint man.


Don't underestimate the difficulty of getting sound pure copper
castings. Low alloy bronzes and brasses (approx 0.5% to 1% tin
or zinc respectively) aren't too bad to cast, high alloy bronzes
and brasses are easy. But casting pure copper is hard, even
with today's technology.

Again, porosity is the problem, and that should show up on
radiographs, as it does for R666 (which certainly shows evidence
of being melted in atmosphere, though not necessarily evidence
of being cast), but none of the other artifacts presented show
that sort of porosity.


See:
http://www.iwaynet.net/~wdc/copper.htm

The 4th and 5th pictures down.

I believe we are agreed that only atmospheric casting was within
reach of the ancient Native Americans (or ancient Old World
founders for that matter), so we *should* see characteristic
porosity in any pure copper items they attempted to cast. Now
of course the Old Worlders had the advantage of ores which
did contain suitable deoxidizers. They weren't actually casting
pure copper. But the Michigan copper was essentially pure
native copper.



Isn't it just possible that you focus too strongly on perfect casting
- the imperfections resulting from casting may not have been a real
big deal to the ancient people.

--
SIR - Philosopher unauthorised
-----------------------------------------------------------------
The one who is educated from the wrong books is not educated, he is
misled.
-----------------------------------------------------------------
  #67   Report Post  
Old June 29th 04, 08:09 AM
Seppo Renfors
 
Posts: n/a
Default Copper Casting In America (Trevelyan)



Tom McDonald wrote:

Gary Coffman wrote:

[..]
As I mentioned previously, surface blisters are not what we're
looking for in terms of the porosity characteristic of pure copper
casting. What we need to see is a foam of microscopic bubbles,
and clusters of tiny visible bubbles deep in the metal on the
radiographs. That's absent from the other radiographs on the
site.


Yes, that's why I was interested in your take on R666/55786.
If there were other good examples of melted copper, I'd have
expected that the web site would have presented them.


IT DOES!! It has been pointed to several times already. Your recent
posting is regurgitating what you have posted before. An apparent
casual visual inspection by the Museum curator, nothing more. Here is
the URL again - and don't forget to scroll down a bit!!

http://www.iwaynet.net/~wdc/copper.htm

As it is,
it looks as though I'll have to dig for other examples that
might show casting.


Listen if the seriousness of your "looking" is equal to your looking
on the web site - give it a miss. You wouldn't see anything anyway.

--
SIR - Philosopher unauthorised
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Old June 29th 04, 09:05 AM
Seppo Renfors
 
Posts: n/a
Default Copper Casting In America (Trevelyan)



Tom McDonald wrote:

Eric Stevens wrote:

On Mon, 28 Jun 2004 13:22:35 -0400, Gary Coffman
wrote:


On Mon, 28 Jun 2004 17:38:04 +1200, Eric Stevens wrote:


[..]

While not directly addressing the point, you may be interested in
http://www.lehigh.edu/~inarcmet/papers/jfa022002.pdf

While not Egyptian, and the artifacts analyzed show evidence of
being wrought rather than cast, the chemical analysis does back
my position. The metals being worked were alloys, not pure native
copper.



As I said, it all depends upon what you mean by 'pure'.


Eric,

In the context of this thread, at least its original context,
the copper was native copper in the upper Great Lakes area of
the US and Canada. That copper is typically well over 99% pure
out of the ground, and does not have to be smelted to remove
impurities. If another context is in evidence, then a
definition of the term 'pure' is needed.


http://www.dayooper.com/Networks.JPG

The copper may well be 99% pure - what about the rest? It isn't every
day people find huge lumps of pure copper without impurities embedded
within it. This is the dilemma that people bypass and ignore.

This has a good story about the Great lakes Copper deposits.
http://www.geo.msu.edu/geo333/copper.html

[..]


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Old June 29th 04, 10:26 AM
Gary Coffman
 
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Default Copper Casting In America (Trevelyan)

On Tue, 29 Jun 2004 05:48:01 GMT, Seppo Renfors wrote:
Gary Coffman wrote:
Don't underestimate the difficulty of getting sound pure copper
castings. Low alloy bronzes and brasses (approx 0.5% to 1% tin
or zinc respectively) aren't too bad to cast, high alloy bronzes
and brasses are easy. But casting pure copper is hard, even
with today's technology.

Again, porosity is the problem, and that should show up on
radiographs, as it does for R666 (which certainly shows evidence
of being melted in atmosphere, though not necessarily evidence
of being cast), but none of the other artifacts presented show
that sort of porosity.


See:
http://www.iwaynet.net/~wdc/copper.htm

The 4th and 5th pictures down.


Those pictures do not show any evidence of the characteristic
porosity copper casting would produce. The single large surface
bubble is a blister, common when the surface of a wrought piece
is overheated. Compare it to the radiograph of R666. The latter
does show the characteristic deep pattern of porosity of an at least
partially melted copper object.

I believe we are agreed that only atmospheric casting was within
reach of the ancient Native Americans (or ancient Old World
founders for that matter), so we *should* see characteristic
porosity in any pure copper items they attempted to cast. Now
of course the Old Worlders had the advantage of ores which
did contain suitable deoxidizers. They weren't actually casting
pure copper. But the Michigan copper was essentially pure
native copper.



Isn't it just possible that you focus too strongly on perfect casting
- the imperfections resulting from casting may not have been a real
big deal to the ancient people.


But the imperfections due to casting pure copper *would* produce the
characteristic porosity which is *not* seen in any of the pieces other
than R666. As I have remarked in other posts, it is possible that this
single sample may have been melted due to a cause other than
deliberate casting, so by itself it is not conclusive evidence for a
copper casting technology, though it is suggestive.

In any event, none of the other objects show the porosity signature
of atmospheric casting. So even if the ancient people found flawed
castings acceptable (and such castings would be weak and brittle),
the lack of porosity is strong evidence that none of these particular
items, with the possible exception of R666, were cast.

Gary
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Old June 29th 04, 09:40 PM
Tom McDonald
 
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Default Copper Casting In America (Trevelyan)

Seppo Renfors wrote:

Tom McDonald wrote:

Gary Coffman wrote:


[..]

As I mentioned previously, surface blisters are not what we're
looking for in terms of the porosity characteristic of pure copper
casting. What we need to see is a foam of microscopic bubbles,
and clusters of tiny visible bubbles deep in the metal on the
radiographs. That's absent from the other radiographs on the
site.


Yes, that's why I was interested in your take on R666/55786.
If there were other good examples of melted copper, I'd have
expected that the web site would have presented them.



IT DOES!! It has been pointed to several times already. Your recent
posting is regurgitating what you have posted before. An apparent
casual visual inspection by the Museum curator, nothing more. Here is
the URL again - and don't forget to scroll down a bit!!

http://www.iwaynet.net/~wdc/copper.htm


Seppo,

As Gary has pointed out, only the item R666 (site report
artifact number), 55786 (Milwaukee Public Museum designation)
shows the characteristic porosity of melted copper; the other
copper artifacts on that page do not. My purpose in mentioning
Alex Barker's observation was merely to have an eye witness to
the artifact in question, to verify that it indeed does look
like a lump of accidentally melted or discarded copper, as
opposed to something that might have been, for instance, trimmed
off the cast after cooling. The other relevant facts about it
seem to have been adequately presented on Connor's web site.


As it is,
it looks as though I'll have to dig for other examples that
might show casting.



Listen if the seriousness of your "looking" is equal to your looking
on the web site - give it a miss. You wouldn't see anything anyway.


So far, at least as presented on this ng, the only copper
artifact that was certainly the result of melting is R666/55786.
The other artifacts Mallery (and Connor) seem to think were
cast either weren't, or don't have sufficient diagnostic
information presented to decide.

Tom McDonald



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