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What is the cause of this texture?
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<p>[QUOTE="shanxi, post: 4150101, member: 101607"]Normally this effect is called crystallization, which is half right half wrong. Wrong because the silver was already crystalline before the structure was formed, right because it is partly based on an improvement of the crystals.</p><p><br /></p><p>You have to know that copper and silver can be mixed homogenously at high temperatures in the melt, but they try to separate at low temperatures and do not form defined mixed crystals.</p><p><br /></p><p>So when copper is melted together with silver, a homogeneous liquid is formed. When cooled down quickly, the two metals remain "mixed" for the time being. This results in "contaminated" crystals of two metals that do not like each other at low temperatures.</p><p><br /></p><p>During the so called "crystallization", impurities such as copper are excluded. Mostly a closed silver layer forms on the surface of the coin, under this layer you find the structure recognizable on your coin. If the copper (between the silver areas) is dissolved out by oxidation, the structure can be seen more clearly. Inside, however, you can usually still see silver and copper phases if you do cross sections.</p><p><br /></p><p>The process is very slow, it can be accelerated by temperature, but then normally not such nice structures are formed. A short-lived fire, as is sometimes assumed, cannot replace 2000 years.[/QUOTE]</p><p><br /></p>
[QUOTE="shanxi, post: 4150101, member: 101607"]Normally this effect is called crystallization, which is half right half wrong. Wrong because the silver was already crystalline before the structure was formed, right because it is partly based on an improvement of the crystals. You have to know that copper and silver can be mixed homogenously at high temperatures in the melt, but they try to separate at low temperatures and do not form defined mixed crystals. So when copper is melted together with silver, a homogeneous liquid is formed. When cooled down quickly, the two metals remain "mixed" for the time being. This results in "contaminated" crystals of two metals that do not like each other at low temperatures. During the so called "crystallization", impurities such as copper are excluded. Mostly a closed silver layer forms on the surface of the coin, under this layer you find the structure recognizable on your coin. If the copper (between the silver areas) is dissolved out by oxidation, the structure can be seen more clearly. Inside, however, you can usually still see silver and copper phases if you do cross sections. The process is very slow, it can be accelerated by temperature, but then normally not such nice structures are formed. A short-lived fire, as is sometimes assumed, cannot replace 2000 years.[/QUOTE]
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What is the cause of this texture?
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