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<p>[QUOTE=&quot;Dawnno, post: 610957, member: 10171&quot;]It&#039;s all chemistry, folks.&nbsp; I would think that in the chemical/metallurgical literature journals there might have been some studies done on the rates of oxidation, that would narrow down categories of age for a metal.&nbsp;&nbsp; Interesting project to take on... nope, not today.</p><p><br /></p><p>Remember, boys and girls: </p><p>tarnish = oxidation = adding an oxygen molecule</p><p>like ordinary rust:</p><p>Iron + Water + Oxygen = Rust</p><p>i.e. 4 Fe + 6 H2O + 3 O2 → 4 Fe(OH)3</p><p>, and so iron rusts, dehydrates and you get Fe2O3.</p><p><br /></p><p>24 K Gold = elemental gold = uniquely stable element that has no place for O to attach.</p><p>Alloys = molecular conglomerates [a <i>solid solution</i>, if you can imagine] of metals, like Cu, or Zn, or Sn added, which bind with Oxygen... so, Cu++ will bind with O-2...&nbsp;&nbsp; and it gets more complicated when you add other compounds...</p><p>&quot;Verdigris is the common name for a ... natural patina formed when copper, brass or bronze is weathered and exposed to air or seawater over time. It is usually a basic copper carbonate (Cu2CO3(OH)2), but near the sea will be a basic copper chloride (Cu2(OH)3Cl). </p><p><br /></p><p>[sorry, no superscripts or subscripts in the font so the formulas are hard to read]</p><p><br /></p><p>So, for now, &#039;going by eye&#039; maybe as effective, and &quot;superior knowledge,&quot; as studying years of metallurgical chemistry on oxidation rates and colorimetry.[/QUOTE]</p><p><br /></p>

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