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<p>[QUOTE=&quot;DW-coins, post: 1304158, member: 33380&quot;]Very interesting topic and from the answers I would venture to say few of you are chemists. Actually, few people in general are chemists, so I think the numbers are on my side. :smile Although I am a chemist with over 25 yrs experience, the following is only my opinion and may or may not have anything to do with reality.</p><p><br /></p><p>I think the issue has less to do with the composition of the plastic mint packaging (or philo, or whatever cool commercial name they gave it) and has everthing to do with the construction of the packaging. This plastic these coins are held in is very porous and not air tight, hence air flows in and out at ease. Now look at what surrounds any given mint set - in most cases there&#039;s a small paper note describing the set with a message from the mint director, a small cardboard insert and the envelope itself. All paper made from this period is filled with chemicals, especially inorganic acids. Just take a look at any book from the 60&#039;s or 70&#039;s (or the 80&#039;s for that matter), the pages are all yellow and beginning to be brittle. You often hear of people having paper based items treated to neutralize the acid in the paper and stop the degradation. Although I do not know for a fact the paper used by the mint is filled with acid, I would say its highly highly likely that the paper is the same as all other paper products of that era and is filled with acids. Therefore I would content that the discoloration of the coins has much more to do with their environment outside the porous plastic container than with the plastic container itself.[/QUOTE]</p><p><br /></p>

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