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<p>[QUOTE=&quot;Kentucky, post: 1770925, member: 33176&quot;]Wow, contentious thread.&nbsp; I am a chemist and a coin collector/hoarder, but I am an Organic Chemist, which encompases compounds of carbon in general.&nbsp; BadThad is much more of a metals and surfaces expert than I am. </p><p>&nbsp;</p><p>One of the first things we should understand when we talk about subjects like this is that language is imprecise and is mostly useful to beat each other over the head with.&nbsp; That being said, what is the difference between corrosion and tarnish - actually in my estimation, nothing.&nbsp; The difference comes about in the thickness of the layer deposited on the surface of the coin.&nbsp; Talking about silver specifically, if this layer is due to oxygen it is silver oxide and if it is due to sulfur (or more specifically sulfur compounds, including from the sulfates possibly used in paper manufacture, or from sulfur dioxide due to flatulence and the eggs you had for breakfast : - ))it is silver sulfide.&nbsp; The identity at low thickness is not really important since at this stage either would be somewhat transparent.&nbsp; The colors are going to come about due to the thickness and what it does to the reflected light, the thicker the layer, the darker until it becomes opaque.</p><p>&nbsp;</p><p>I would say it is toning until it becomes opaque and after that call it tarnish. </p><p>&nbsp;</p><p>Now THIS is rambling.&nbsp; Finally, oxidation is not only reaction of a species with oxygen, but can also be the reaction with any species where the reacted species has lost electrons to another species (oxidation is loss of electrons, reduction is gain of electrons - oil rig).[/QUOTE]</p><p><br /></p>

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