FORVM`s Classical Numismatics Discussion Board
Numismatic and History Discussion Forums => Coin Photography, Conservation and Storage => Topic started by: Ashby C on September 02, 2018, 04:42:14 pm
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Greetings,
I am a novice collector of ancient coins (only about 2 weeks along) and was very pleased with the "floating frame" display in which a coin was sent to me by an expert vendor. I purchased a cheap set of "floating frame" coin displays on Amazon. The description states in pertinent part (emphasis supplied), "SIMPLE SET UP: Place and position objects between plastic membranes made of archival safe material and clasp frame together." My question is whether I should trust the representation about the membrane being "archival safe." Do any of you have knowledge or experience that would lead you to be distrustful? Thanks!
Ashby
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I don’t know those frames but I’d say make sure the plastic doesn’t contain any PVC, which could cause severe damage to your coins.
DT
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Their description states that the plastic surfaces are a bit "tacky".....that would concern me a bit.
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Thanks for the replies. The seller (Chinese apparently) stated in response to my email sent through Amazon that the "product is made of PE and PVC." I replied, "Do you mean that the membrane is made of polyethylene terephthalate (PET) and the case is made of polyvinyl chloride (PVC)?" I will let you know if I receive an answer.
Ashby
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These items can look impressive but it is very unlikely that PET is sufficiently flexible to achieve the look of these items. That being said, if you like the coin in that setting and it is not a rarity, you may feel comfortable taking the risk. Many coins sit for years in dealer pvc flips. PVC is not an instant corrosive.
There are other manufacturers who may have better products or be more responsive, because it doesn't really matter what they SAY. It only matters what the stuff IS.
Or perhaps you could cut a section of mylar from a flip and cover the coin.
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For what it's worth, the seller just responded with, "The membrane is made of polyethylene (PE) and the case is made of polyvinyl chloride (PVC)." Assuming that is true, is polyethylene (PE) different from polyethylene terephthalate (PET), and if so, is that difference relevant to its suitability for use in displaying coins? Thanks.
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"The membrane is made of polyethylene (PE) and the case is made of polyvinyl chloride (PVC)."
PVC is only a problem when it contains plasticizers. Hard PVC, used for window frames, is a very stable material.
Pure PE is also unproblematic as long as you keep it out of direct sunlight. Nevertheless it could contain small amounts of stabilizers etc..
But it is very unlikely that the foil of the coin display is pure PE. PE is a semicrystalline polymer and therfore not completely transparent. You know the material from plastic bags. Also I don't think that a PE foil would be able to keep a coin in place, it's not sticky enough.
I rather think that the foil is a PE-copolymer, Poly(ethylene-butylene), or something similar. Also this material is unproblematic if it is used without any additives, which is possible, and maybe "archival safe material" means that it is without additives. Unfortunatelly there are plasticizers for these copolymers, and as long as I do not know for sure if these foils contain plasticizers or not I would keep my fingers off, but maybe I am overcautious.
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I am grateful for the information and advice. I'm attempting to obtain further information about the composition of the membrane. If I learn anything significant I'll post a note.
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I have now been informed the membrane material is PET (polyethylene terephthalate). If true, I understand it is not harmful to coins.
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I assume you want to put the coins on display were you can see them, inside a climate controlled house. Plastics take at least a few years to start to deteriorate in those conditions, probably a lot longer. If the plastic starts to get cloudy or yellow, take the coin out and throw the plastic away. Coins I have seen damaged by PVC were in the soft flips unobserved for more than 10 years. The archival safe flips I use sometimes turn yellow in about 10 - 15 years. They are, even then, presumably still safe, but I still switch them to a new flip if I see any change. The most important thing is to look at them at least a few times a year.
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Thank you. I'll definitely keep an eye on them.