Coin Storage

[Fulvio]

Just wondering how people find the SAFLIPS for long term storage.

Apart from chemicals leaching from the plastic itself, as happens with PVC, the critical performance criteria for any material are its permeability to Moisture and Oxygen, as well as other gaseous contaminants.

For example, I discovered the hard way that LDPE is not impervious to fumes given off by foam cushions and carpets, and posted about it a while back.

At high temperatures, for example,
"polyurethane foam begins to rapidly decompose, releasing gases and compounds such as hydrogen cyanide, carbon monoxide, acetronitrile, acrylonitrile, pyridine, ethylene, ethane, propane, butadine, propinitrile, acetaldehyde, methylacrylonitrile, benzene, pyrrole, toluene, methyl pyridine, methyl cyanobenzene, naphthalene, quinoline, indene, and carbon dioxide. Of these chemicals, carbon monoxide and hydrogen cyanide are considered lethal."

Clearly, some of that decomposition happens at lower temperatures as well. I have a white iPod charging cable which spent a year or so draped over a foam pillow, and the section in contact with the pillow is now yellow. I'd hate to see a coin left in contact with such a pillow. I have some UNC Coronation $2's which turned green inside a sealed LDPE bag left in contact with a cushion.

A quick search for gas permeability turned up these little gems:

http://www.hindawi.com/journals/ijps/2012/302029/ Which although related to food packaging, covers the basic science and methodology in this field.

http://www.faybutler.com/pdf_files/HowHoseMaterialsAffectGas3.pdf is perhaps easier to follow, as it compares permeability coefficients for common materials which might be used for hoses in welding applications. Some of which are films from which coin storage products are made.

Saflips are made of PP, Polypropylene. 2x2's are made of BoPET, otherwise known as Mylar. Standard ziplock bags, such as bank coin bags, are made of LDPE, Low Density PolyEthylene.

LDPE, as we now know, is not sufficiently impervious to gasses in close proximity.

PP and BoPET are much better. However, as you've discovered, self-adhesive 2x2's are problematic on two counts. Firstly, the adhesive has a tendency to let go, especially with large, heavy coins. Once open, there is no barrier to air reaching the coin at all. Secondly, the adhesive itself may be problematic. We don't know what it is, or what chemicals it may leach.

A non-adhesive 2x2 ironed shut provides a perfect, permanent seal, provided you don't allow the hot iron to melt the window of course. A Saflip is not as impervious, but is made of thicker material.

If you look at the chart, Saran is clearly the best barrier that's readily available. However, as it contains Chlorine atoms, we would need to find out how stable it is in the long term, and whether it will eventually leach harmful fumes. Food packaging does not have to survive for many years, so this research may be hard to find.

There are a couple of other options, at least for bulk storage.

HDPE is a very good, stable barrier to just about everything. That's why Acetone comes in HDPE containers. But it isn't clear. PET is clear, is better against gasses, but worse against moisture.

And then there are multi-layered films, such as the printed metallised Mylar you find in Helium balloons and chip packets. Obviously these are opaque, but the sandwich of different materials is designed to be as close to a perfect barrier as possible. In some cases, such as with bags of bulk coins, it may be desirable to seal them inside such (suitably cleaned, naturally) bags. Ideally vacuum-sealed or Nitrogen flooded, should either be available.

[matttheriley]

This is what I want!

http://www.coincabinets.com/pheon.html

[NZCoinerrors]

Wow thanks for the detailed information Fulvio.  Is there anyway to test the plastic used on the cardboard flips?  I have some cheap ones from china but have no idea what plastic they are made of

[ausjack]

After a while PVC goes hard but I don't know how to tell when it's new sorry but hopefully Fulvio will fill us in

This is what I want!

http://www.coincabinets.com/pheon.html

Yes that looks nice Matt but I'd be very careful of any felt type stuff as the 66 proof set is a prime eg of how the blue felt damages the coins, leave the silver with a real smoky appearance :dodgy:

[Fulvio]

Wow thanks for the detailed information Fulvio.  Is there anyway to test the plastic used on the cardboard flips?  I have some cheap ones from china but have no idea what plastic they are made of

The only way to test plastic really is to burn it and analyze the gasses.

But AFAIK, all cardboard mounts use Mylar/BoPET. Its the only stuff that has the right mechanical properties at that thickness.

PVC is easy to identify cos it stinks, basically. And it feels slimy. Just about everything else you're likely to come across is safe in itself. Possibly excepting some food packaging which may have organic additives that might leach. Even chlorides should be safe enough, provided the molecules don't break down, which they shouldn't in normal use. But I personally avoid them anyway, because there are stable alternatives.

Oh, and speaking of avoidance.. a big open metal box? Pass.

[Unicorn]

Oh, and speaking of avoidance.. a big open metal box? Pass.

Well at least yours does have a door .....



:laugh2:

[JeffH]

I am able to collect silica gel sachets from some products I handle. They are commonly used in electronic products to avoid moisture damage during shipping. I scatter them around my storage drawers to keep the humidity low in the vicinity of any coins and banknotes.
Hint; write the date on them and, every now and then, toss away any older ones. If the grains feel soft then toss immediately -they have absorbed as much moisture as they can and will soon start dribbling water (definitely not good).

[ausjack]

Also found in shoe boxes sometimes, so if that isn't a good enough excuse to go shoe shopping ladies I don't know what is, but don't tell the other half I said so :blush2:
You might even be able to get some if you ask the sales person nicely

[Mister T]

Thanks Mister T.  Do you seal them?  I find that holds them firmer so they dont move around and the heat sealer only cost about $20

No I don't bother with that - they do move around but I figured I could fix it easier if they weren't heat-sealed.

[Fulvio]

toss away any older ones.

Umm, no.

Silica Gel is an ADsorbent, not an ABsorbent, and is totally inert (except the indicator in the colour-changing variety, which is toxic if ingested). The water is held on the surface of the pores... many square metres packed inside the structure of the beads.

They can be baked to remove the water, and are reusable indefinitely.

Also, they need to be inside sealed containers. They are useless for removing moisture from the vicinity of coins exposed to the atmosphere.

I would put the coins, containers or albums in closed bags or other airtight containers, and pack both silica gel and oxygen absorbers (basically packets of rust, found in many foods such as wraps and jerky etc, as well as hand warmers) in with them.

[runway]

Can't go wrong with any modern storage systems specifically for coins

[JeffH]

OK, I stand corrected. I will try rejuvenating some old ones.

[oh my florin]

OK, I stand corrected. I will try rejuvenating some old ones.

Just don't bake the coins with them

[Fulvio]

OK, I stand corrected. I will try rejuvenating some old ones.

http://qqjky.qjhbf.servertrust.com/v/vspfiles/info/Silica%20Gel.pdf

[JeffH]

I have tried a very simplistic method -see the picture. After 8 hours sitting on a barely burning heater the weight of the sachets went from 85g to 79g. By my calculation I have removed a little over the equivalent of a teaspoon of water.
The base of the metal bowl was hot enough to touch but you could not keep your hand on it for more than a second, or so. Every now and then  stirred the sachets around to give them all a go at the heat.