The "oily Film" Appearance Of Empty Saflips

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Author	Replies: 3 / Views: 1,778
numis18thc New Member United States 5 Posts	Posted 09/07/2014 7:03 pm Hi, I'm contemplating longer-term storage options for my coins. Several previous threads have discussed at length the various issues of the PVC, "vinyl", the "low plasticizer" versions, mylar and similar polyester-based materials, and various products made from them. But I have a question about Saflips that was not addressed in the previous threads. Encouraged by the "mylar, no plasticizers or oils" description I bought some Saflips. When they arrived, though, I noticed that when the two inner surfaces of a pocket touch each other the area of contact appears to resemble an "oily film" (for lack of a better description). In sunlight, the area of contact shows colors of blue, green and red. I don't think I just got a bad batch of flips, since I have seen this appearance in online photos, such as the area above the coin in this ebay photo: http://www.ebay.com/itm/SAFLIP-2x2-...141389029373 If I take a classic "cardboard and mylar" 2x2 and make the two mylar surfaces touch, they don't look like this--suggesting it is not simply a property of mylar. I live in a very dry climate, ruling out the likelihood of humidity/condensation. I have spent hours searching for an explanation online but haven't found one. Does anyone have any information on why Saflips appear this way, and whether it is something to be concerned about? Thanks, numis18thc Report this Post to the Staff

Sap Moderator Australia 16816 Posts	Posted 09/07/2014 8:45 pm In circumstances like this, colours are caused by the thin film effect - the same byproduct of the laws of optics that generate colours in soap bubbles, oil slicks, some insect wings and even the toning on coins. It occurs whenever light passes through something transparent and just the right thickness. In this case, the plastic sheets the flip is made from are too thick to generate the effect by themselves. What is causing the "thin film" is the interaction between the two inner surfaces of the flip as they come in contact. As I understand it, static electricity is pulling the two pieces of plastic together, trapping a layer of air in between them. So the "agent" generating the thin film and therefore the colour is not oil or solvent, but rather the air itself. Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis Report this Post to the Staff
numis18thc New Member United States 5 Posts	Posted 09/08/2014 10:19 am Thanks for the explanation Sap. Report this Post to the Staff
Mullen Valued Member United States 167 Posts	Posted 09/08/2014 12:42 pm I agree with sap. You can see this exact type of reaction with graded coins. The plastic case shows the same thing on a few I've seen. Report this Post to the Staff
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The "Oily Film" Appearance Of Empty Saflips