First Page
Posted 03/28/2014 07:41 am
Generally in silver/copper alloys Cu is about 5%. Along with Ag (generally blue) it gives you various rainbow colors. If you buy a coin which has been dipped - not brushed (hairlines) you can stick it in an oven say at 400*F and let the copper tone QUICKLY - bringing back some ORIGINAL color.
Here is my merry-go-round response to your question.
Its personal ...
Initially, bare Cu metal atoms react with air to form the pink oxide, cuprite, Cu2O, which has Cu+1 cations. This gradually oxidizes further to the black oxide, tenorite, CuO, with Cu+2 ions. The black sulfide CuS also sometimes forms. In the presence of moisture, the blackish layer slowly reacts with sulfur dioxide and carbon dioxide from the air to eventually form the patina, which is a mixture of 3 minerals:
brochantite, a green, hydrated copper sulfate, Cu4SO4(OH)6
malachite, the green, hydrated copper carbonate Cu2CO3(OH)2
azurite, the blue, hydrated copper carbonate Cu3(CO3)2(OH)2
In these compounds, copper atoms from the metal surface have been fully oxidized into Cu+2 (cupric) ions. The rate of patina formation and the proportion of the components depend upon humidity and handling.
It does bother me when collectors tell me I only like WHITE. Never been to New Orleans in a TIME MACHINE in the 1800's and view the top coin in a Morgan dollar bank roll out of the bank?
Here is my merry-go-round response to your question.
Its personal ...
Initially, bare Cu metal atoms react with air to form the pink oxide, cuprite, Cu2O, which has Cu+1 cations. This gradually oxidizes further to the black oxide, tenorite, CuO, with Cu+2 ions. The black sulfide CuS also sometimes forms. In the presence of moisture, the blackish layer slowly reacts with sulfur dioxide and carbon dioxide from the air to eventually form the patina, which is a mixture of 3 minerals:
brochantite, a green, hydrated copper sulfate, Cu4SO4(OH)6
malachite, the green, hydrated copper carbonate Cu2CO3(OH)2
azurite, the blue, hydrated copper carbonate Cu3(CO3)2(OH)2
In these compounds, copper atoms from the metal surface have been fully oxidized into Cu+2 (cupric) ions. The rate of patina formation and the proportion of the components depend upon humidity and handling.
It does bother me when collectors tell me I only like WHITE. Never been to New Orleans in a TIME MACHINE in the 1800's and view the top coin in a Morgan dollar bank roll out of the bank?
