Broken coins

I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized barbarous imitation of an
ancient Thasos tetradrachm, one of the areas I specialize in. I have
an official issue, a number of these barbarous issues thought to have
been struck not by Greeks in Thasos but by nearby Thracians in the
first century AD, an ancient "fouree" counterfeit, several modern
counterfeits, and a coin test-cut in ancient times to determine its
authenticity. Why not add a broken coin to this set. g It's very
interesting, actually, illustrating how silver changes over time,
becoming brittle. Time changes all... I haven't photographed the coin
yet but will.

On 9 Apr 2004 14:27:58 -0700, Reid Goldsborough
wrote:

I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized barbarous imitation of an
ancient Thasos tetradrachm, one of the areas I specialize in. I have
an official issue, a number of these barbarous issues thought to have
been struck not by Greeks in Thasos but by nearby Thracians in the
first century AD, an ancient "fouree" counterfeit, several modern
counterfeits, and a coin test-cut in ancient times to determine its
authenticity. Why not add a broken coin to this set. g It's very
interesting, actually, illustrating how silver changes over time,
becoming brittle. Time changes all... I haven't photographed the coin
yet but will.

So if a coin is brittle it implies a relatively high purity (90-99%)
silver alloy does it not?

writes:

Why not add a broken coin to this set. g It's very
interesting, actually, illustrating how silver changes over time,
becoming brittle.

So if I wait long enough, I can become the proud owner of a busted bust half
half? :-)

"Jorg Lueke" wrote in message
news
On 9 Apr 2004 14:27:58 -0700, Reid Goldsborough
wrote:

I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized barbarous imitation of an
ancient Thasos tetradrachm, one of the areas I specialize in. I have
an official issue, a number of these barbarous issues thought to have
been struck not by Greeks in Thasos but by nearby Thracians in the
first century AD, an ancient "fouree" counterfeit, several modern
counterfeits, and a coin test-cut in ancient times to determine its
authenticity. Why not add a broken coin to this set. g It's very
interesting, actually, illustrating how silver changes over time,
becoming brittle. Time changes all... I haven't photographed the coin
yet but will.

So if a coin is brittle it implies a relatively high purity (90-99%)
silver alloy does it not?

I don't see why, Jorg.
I don't have much experience with silver alloys, but the mechanism of age-hardening
relies upon the presence of alloying elements.

Hehe
The time base on the graphs I have at hand doesn't extend as far as 2000 years (or
even nearly that much!) but the effect is most pronounced at a certain specific
composition, but negligible with purity.

Migration of alloying material towards grain boundaries can be one mechanism for
age-hardening (whether it is 6-hour in a temp-controlled furnace, or 2000 years in a
coin cabinet) so I wouldn't be using brittleness as an indicator of purity.

Hardness (and hence brittleness) is almost always enhanced by the addition of
alloying elements - the softest mix being the purest.

Crystallisation as such (by itself) is insufficient as an hardening mechanism. High
carbon steel (bad analagy, but its the best I can troll up immediately) can exist in
two forms (and more!) depending on heat treatment. Heated and quenched it is
glass-hard, consisting of needle-like crystals of martensite. The same stuff, if
heated again and allowed to cool very slowly, will precipitate much larger crystals
of ferrite (with others) and will be be *much* softer and tougher (less brittle) even
though crystal growth has been deliberately promoted.

None of this happens with pure iron, BTW. It needs the alloying element carbon.

So, in a word, Jorg:

===
No!
===

Of course, I could be wrong.

--
Jeff

On Sat, 10 Apr 2004 11:51:45 +1000, A.Gent wrote:


"Jorg Lueke" wrote in message
news
On 9 Apr 2004 14:27:58 -0700, Reid Goldsborough
wrote:

I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized barbarous imitation of an
ancient Thasos tetradrachm, one of the areas I specialize in. I have
an official issue, a number of these barbarous issues thought to have
been struck not by Greeks in Thasos but by nearby Thracians in the
first century AD, an ancient "fouree" counterfeit, several modern
counterfeits, and a coin test-cut in ancient times to determine its
authenticity. Why not add a broken coin to this set. g It's very
interesting, actually, illustrating how silver changes over time,
becoming brittle. Time changes all... I haven't photographed the coin
yet but will.

So if a coin is brittle it implies a relatively high purity (90-99%)
silver alloy does it not?

I don't see why, Jorg.
I don't have much experience with silver alloys, but the mechanism of
age-hardening
relies upon the presence of alloying elements.

Hehe
The time base on the graphs I have at hand doesn't extend as far as 2000
years (or
even nearly that much!) but the effect is most pronounced at a certain
specific
composition, but negligible with purity.

Migration of alloying material towards grain boundaries can be one
mechanism for
age-hardening (whether it is 6-hour in a temp-controlled furnace, or
2000 years in a
coin cabinet) so I wouldn't be using brittleness as an indicator of
purity.

Hardness (and hence brittleness) is almost always enhanced by the
addition of
alloying elements - the softest mix being the purest.

Crystallisation as such (by itself) is insufficient as an hardening
mechanism. High
carbon steel (bad analagy, but its the best I can troll up immediately)
can exist in
two forms (and more!) depending on heat treatment. Heated and quenched
it is
glass-hard, consisting of needle-like crystals of martensite. The same
stuff, if
heated again and allowed to cool very slowly, will precipitate much
larger crystals
of ferrite (with others) and will be be *much* softer and tougher (less
brittle) even
though crystal growth has been deliberately promoted.

None of this happens with pure iron, BTW. It needs the alloying element
carbon.

So, in a word, Jorg:

===
No!
===

Of course, I could be wrong.

--
Jeff

My understanding is (an it certainly is not complete) that silver going
brittle happens because of the action of copper in the alloy. I thought
this occurred only with a ceratn percentage of copper alloy. I think
steel behaves differently than silver as do other elements.

"Jorg Lueke" wrote in message
news
On Sat, 10 Apr 2004 11:51:45 +1000, A.Gent wrote:


My understanding is (an it certainly is not complete) that silver going
brittle happens because of the action of copper in the alloy. I thought
this occurred only with a ceratn percentage of copper alloy. I think
steel behaves differently than silver as do other elements.


Which is pretty much exactly what I said. :-)


The point which may need re-stating, however, is that hardening over time is *not* an
indicator of metal purity. (To answer your original question.)

--
Jeff

On Sat, 10 Apr 2004 13:39:14 +1000, A.Gent wrote:


"Jorg Lueke" wrote in message
news
On Sat, 10 Apr 2004 11:51:45 +1000, A.Gent
wrote:


My understanding is (an it certainly is not complete) that silver going
brittle happens because of the action of copper in the alloy. I
thought
this occurred only with a ceratn percentage of copper alloy. I think
steel behaves differently than silver as do other elements.


Which is pretty much exactly what I said. :-)


The point which may need re-stating, however, is that hardening over
time is *not* an
indicator of metal purity. (To answer your original question.)

--
Jeff

This site seems to disagree with you :-)
http://www.corrosion-doctors.org/Artifacts/silver.htm

This one seems copper and other elements
http://www.nlr.nl/public/library/2002/2002-224-dcs.html

There's other similar web pages. To me what it sounds like is there are
certain proportions of certain alloys that are O.K. at high temperatures
but not supported at room temperature. Over time the alloyed material
does something at the microscopic level whch leads to this embrittlement.
The percentage of alloy does seem to play a role in this.

Do those sites make sense to you?

"Jorg Lueke" wrote in message
news
On Sat, 10 Apr 2004 13:39:14 +1000, A.Gent wrote:


"Jorg Lueke" wrote in message
news
On Sat, 10 Apr 2004 11:51:45 +1000, A.Gent
wrote:


My understanding is (an it certainly is not complete) that silver going
brittle happens because of the action of copper in the alloy. I
thought
this occurred only with a ceratn percentage of copper alloy. I think
steel behaves differently than silver as do other elements.


Which is pretty much exactly what I said. :-)


The point which may need re-stating, however, is that hardening over
time is *not* an
indicator of metal purity. (To answer your original question.)

--
Jeff

This site seems to disagree with you :-)
http://www.corrosion-doctors.org/Artifacts/silver.htm

This one seems copper and other elements
http://www.nlr.nl/public/library/2002/2002-224-dcs.html

There's other similar web pages. To me what it sounds like is there are
certain proportions of certain alloys that are O.K. at high temperatures
but not supported at room temperature. Over time the alloyed material
does something at the microscopic level whch leads to this embrittlement.
The percentage of alloy does seem to play a role in this.

Do those sites make sense to you?

Yes... perfectly. Don't they agree with what I said?

Jorg, I must not be making myself clear. ;-(

Your original question: "...So if a coin is brittle it implies a relatively high
purity (90-99%)
silver alloy does it not?"

....I answered with "no", which is totally consistent with what I've posted today, and
what the above-cited websites state.

Brittleness *doesn't* imply a relatively high purity. It implies (*requires*!) the
presence of significant alloying elements.

I'm sorry, Jorg. Am I not making myself clear? ;-( (again)

Cheers
--
Jeff

(Reid Goldsborough) wrote
I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized ...

I lost a Ptolemy II tetradrachm to a show-and-tell. I took some
ancients to my local coin club for a presentation and a nice old man
dropped the tet and when it hit the hard old linoleum floor, it broke
in two. It was crystalized and honeycombed inside. I ate the loss and
learned a lesson: No more show-and- tells, at least not with ancients.

Michael
ANA R-162953
"It paid for the Library of Alexandria"

"Michael E. Marotta" wrote in message
om...
(Reid Goldsborough) wrote
I received my first broken coin in the mail yesterday. I bought it
that way. g It's a heavily crystalized ...

I lost a Ptolemy II tetradrachm to a show-and-tell. I took some
ancients to my local coin club for a presentation and a nice old man
dropped the tet and when it hit the hard old linoleum floor, it broke
in two. It was crystalized and honeycombed inside. I ate the loss and
learned a lesson: No more show-and- tells, at least not with ancients.

Michael
ANA R-162953
"It paid for the Library of Alexandria"

Jeepers - I'd *love* to do a photomicrograph of the break.

Have you - could you - will you?
Pretty please?

--
Jeff