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<p>[QUOTE=&quot;Hobo, post: 1700461, member: 11521&quot;]Heat does affect both sides but the effects of an expanding air bubble in the coin can differ from one side to the other. </p><p><br /></p><p><br /></p><p><br /></p><p>Correct. Suppose a trapped air bubble happens to be closer to one side of a coin. When the coin is heated the pressure in the trapped air bubble will increase. If the coin is heated to a high enough temperature the metal in the coin will become plastic which will allow the air bubble to expand in size (and decrease the pressure inside the air bubble). The bubble will expand in the direction of least resistance which is usually where the metal is thinnest between the air bubble and the surface of the coin.[/QUOTE]</p><p><br /></p>

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