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<p>[QUOTE=&quot;bigbruiser94, post: 1816199, member: 46403&quot;]During cooling, crystalisation occurs, the crystal forming around &quot;seeds&quot; which are molecules of the elemental metals. There is a slight tendency for the elements with the highest melting point to start to crystalise first, and this can lead to small localised areas with slightly higher or lower concentrations of the constituent elements. In ternary alloys (three elements) three pairs of binary (two elements) alloys can also form. These areas of variable alloy are usually of microscopic proportion, but can sometimes be large enough to be visually discernable.</p><p>Copper oxidises and forms other salts fairly readily whereas gold is almost completely inert, and silver lies in between, although it is fairly unreactive. This means that if some parts of the alloy are copper rich, and are exposed on the surface of the coin, then it is possible for these parts to exhibit toning or tarnishing. The red spots are areas with a higher copper </p><p><br /></p><p>Part 2 is because it is not caused by sulfer but by higher copper areas[/QUOTE]</p><p><br /></p>

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