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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. |
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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? |
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"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 |
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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. |
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"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 |
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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? |
#8
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"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 |
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#10
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"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 |
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