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<p>[QUOTE=&quot;desertgem, post: 890740, member: 15199&quot;]I would say a problem free coin in a mylar flip that has been heat sealed. No chance of any gas exchange. The mylar should be extremely stable at normal temperatures , humidity wouldn&#039;t matter since it was sealed, and probably equal with rigid plastic for becoming brittle over 50 years.&nbsp; I don&#039;t believe that either was readily available in 1960, so we have no precedence.&nbsp; </p><p><br /></p><p>I think that as an experiment I could keep a coin in even a <b>PVC</b> flips and not have it damaged over 50 years IF&nbsp; I kept it in a <b>normal room environment AND EXAMINED</b> it ever few months, and <b>rinse it in acetone</b> if I saw any evidence of Plasticizer migration. These problems do not occur overnight. JMHO.&nbsp; Of course, my expected lifetime falls short of 50 more yrs <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie3" alt=":(" unselectable="on" unselectable="on" /> , so someone else would have to do it.[/QUOTE]</p><p><br /></p>

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