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<p>[QUOTE=&quot;Just Carl, post: 139905, member: 4552&quot;]Yes, oxygen is needed to brown the copper. Not to say that a coin won&#039;t brown in a holder(I&#039;m not sure), but I do believe many coins will remain red indefinitely in a slab. Copper turns brown when it reacts with oxygen, particularly in the presence of sulfur, to form copper oxide.</p><p><br /></p><p>True, but you would think they would offer something so your coins stay shiney your whole life time, I am personally a paranoid person so I store my coins in an airtight box that has a dehumidifier and CO2 pumped in to replace the air, exept for my toning coins which I leave out in random places so they will get vetilation and light for toning.</p><p><br /></p><p>The above is somewhat misleading. &quot;particularly in the presence of sulfur&quot;&nbsp; or &quot; CO2 pumped in to replace the air&quot;</p><p>The facts are as follows. When Copper is exposed to MOIST air it slowly reacts with the Oxigen to form Cu2O. This IS the start of the Copper discoloration. Then the Cu2O begins to react with any CO2 present to form [CuCO3-Cu(OH)2] known as Copper Carbonate. This is a slight greenish discoloration on the Copper coins sometimes called a Patina. NOTE! so far no Sulfur is required to do anything.</p><p>Now if there is any Sulfur in the area in the form of H2SO3 or H2SO4 it will react with the Copper Carbonate to form CuSO3 or 4. SULFUR DOES NOT REACT WITH COPPER directly. These are normally air born acids due to a Sulfur burning invironment such as a power station or steel mill. The Sulfur released is SO or SO2 and in the air combines with moisture (H OH) to form air born acid and during rains sometimes called acid rain. Note! (H OH) is the Hydroxide commonly known as H2O or water. </p><p><br /></p><p>Sorry for the chem lesson but that should clear up copper presevation a little.[/QUOTE]</p><p><br /></p>

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