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Storage Damage And A Quest To Have That Sorted For Good - In Depth Explaini

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New Member

Denmark
29 Posts
 Posted 03/18/2021  09:07 am Show Profile   Bookmark this topic Add bw1001 to your friends list Get a Link to this Message
Hi guys,

Back again and in need of help
I've apparently been conducting a very unfortunate experiment (needless to say, unwillingly) for the past...many years and today it became obvious that I was doing something wrong. I do not invest that much in the way I store the coins and always believed, for no reason, that plastic ziplock bags are the perfect cheap solution (easy to write on for inventory purposes as well). Well, while searching for some coins today within the ancient sector, I've noticed that quite a few have "gone bad". So I went back to my home made catalogue to see their initial state and to my very sad surprise, there was definitely something going on with them.

Some of the more obvious signs were
- white residue that would leave a powder like mark on both the coin and the bag (noticeable mostly on greek bronze coins)
- a considerable darkening (it doesn't look like it's a new layer of patina) of certain silver coins (a few denarii and on almost all the republic coins)
- change of patina colouring (they haven't been out of that sealed bag for ages) and signs of potential oxidation on some of the follises

What is strange is that I cannot find an obvious pattern on which type of coins are getting affected as the storage conditions/bags and materials of the coins are the same, yet the outcome varies.

I've read a few threads on storage, but none had those sort of damages so I was wondering if someone could explain what exactly it is going on. I'd also like to know if I can "fix" the already damaged ones or if the damage is permanent and what would others recommend as affordable alternatives to my stupid solution of using cheap ziplock bags

Cheers,
BW
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United States
20201 Posts
 Posted 03/18/2021  09:31 am  Show Profile   Bookmark this reply Add just carl to your friends list Get a Link to this Reply
Difficult to know what happened. I keep many coins in Zip Lock plastic bags. I've found that it is necessary to push out as much air as possible when closing. Sounds like you locked in something in those bags.
just carl
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Canada
4125 Posts
 Posted 03/18/2021  09:38 am  Show Profile   Bookmark this reply Add oriole to your friends list Get a Link to this Reply
The material in zip-lock bags is safe for food and hence safe for coins. So it may not be the fault of the bags.
New Member
Denmark
29 Posts
 Posted 03/18/2021  09:46 am  Show Profile   Bookmark this reply Add bw1001 to your friends list Get a Link to this Reply
Hi Carl,

it could well be the case, even though I have taken all precautions to avoid that since...forever (latex free gloves, mask, d30 cloths and have even padded my scale - but apparently was too cheap to spend some cash on proper storage) :(

the ones I am worried the most is the ones affected by the "white powder" as it seems to corrode them

I've changed them to new bags and will keep an eye on their development, but would still like to find a solution to remove that and find out what it is (any chemists out here?)

that is the sort of residue that it leaves (they have been stored and untouched for ages)



New Member
Denmark
29 Posts
 Posted 03/18/2021  09:47 am  Show Profile   Bookmark this reply Add bw1001 to your friends list Get a Link to this Reply
@oriole

that puts my mind to rest a bit
thank you

there is still something going on and I do not know what :(
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United States
241 Posts
 Posted 03/18/2021  10:32 am  Show Profile   Bookmark this reply Add Kcm to your friends list Get a Link to this Reply
It might be interesting to zip a hygrometer into one of your bags and trace its measure as you store it first in a high relative humidity environment for a week or two and then move it to one more arid and then back. I strongly suspect that H2O molecules can breach the seal. If so, extreme fluctuations in temperature combined with electrolysis of the metals in a coin's alloy as well as those in nearby coins could easily come into play. Your coins may be electroplating one another. Then again, maybe not. Mine's just a course of investigation -- never an explanation.

Kevin
Given the option of choosing between a very interesting coin or a rather valuable one, I'd choose the former every time . My vexation lies in the fact that the two so often coincide.
New Member
Denmark
29 Posts
 Posted 03/18/2021  12:03 pm  Show Profile   Bookmark this reply Add bw1001 to your friends list Get a Link to this Reply
Hi Kevin

That is a very very very interesting thought. If that's the case, I'd almost take my hat off for the physics behind it ,if it wasn't messing with my coins

It is definitely a possibility and one that I haven't thought of. I do keep them basically on top of each other (albeit in a fairly dry environment) thinking that the bags will separate/protect them,so the context is there. Not to mention that I have been doing some cleaning on some of them, so copper might have transferred on the glove and onto the next coin.

However, it'll be a while until I can conduct that test as I don't have a hygrometer and all hardware stores are still closed, with delivery taking ages.

The next vital question will be if the damage is permanent or if it can be fixed (having my fingers crossed for the latter)
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United States
4654 Posts
 Posted 03/18/2021  2:06 pm  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply

Quote:
any chemists out here?


Yes. The problem is that I've never studied this kind of stuff, and it can be very situation-specific.

Here is what I can say about the plastic in ziplock bags (polyethylene)

1. It will let oxygen in through the plastic; it lets in far less water vapor than oxygen.

2. While what @oriole says is true about the polyethylene needing to pass FDA requirements for food contact, this does not mean there are no added chemicals in the bags. There definitely is. Slip agents are substances added in plastics at very low levels (usually less than 1,000 ppm), but they work by migrating to surface of the plastic, which means your coins could be in contact with them. I am relatively certain the plastic in Ziploc bags contain this kind of ingredient. Could they form a whitish deposit on your coin? Yes.
Would they corrode it? I think this is less likely than airborne substances causing the corrosion.
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United States
535 Posts
 Posted 03/18/2021  2:40 pm  Show Profile   Check Billie's eBay Listings Bookmark this reply Add Billie to your friends list Get a Link to this Reply
There is also a lot to be said on not storing dissimilar metals together.

Small silica gel desiccant packets are cheap and readily available.

You can slip them right in the baggies.
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Turkey
785 Posts
 Posted 03/18/2021  7:15 pm  Show Profile   Bookmark this reply Add molydeii to your friends list Get a Link to this Reply
Hi BW, welcome to the forum.

First of all, I am sorry to hear what happened to your coins. I hope it's nothing serious and you can manage to solve it somehow.

White powder makes me thing biodegradable plastics. I believe any food grade plastic has a low chance to be biodegradable, but still it can be a reason. I know for sure that soft plastics contain harmful additions to coins. back in 2005-06, I also do teh same thing with modern uncirculated coins, simply tuck them in brand new ziplocs. Unlike your coins, modern coins showed a reaction in their surface (mostly odd discoloration( in less than six months) so I did my reserach and changed them all. I did the old wire and fire test and found out that my ziplocs had PVC in them.

Having said that, nothing happens overnight. I think specially with ancient coins, it's best to switch into numismatics safe hard plastics (capsules). I have been using capsules since 2006 with modern coins and except for a few plated coins I never had any problem.

I thnk under no circumstances soft plastics is a way to store coins for medium or long periods, ancient or modern.

One another thing affecting your coins may be humidity. Do you live in a humid area, close to the sea or a lake? I think its well known that humidity in teh air affects soft palstics faster than dry climates.

Should you decide to clean any kind of damage on your ancients, I think you need to be very careful and consult to professionals. I am sure many others will be glad to help you in that on forum.

Something off topic is, I'm a very avid collector of modern (post-1900s) Denmark coins. I believe circulation coins have such beautiful desings that makes our coins here look like monopoly money.
My tradelist and some wanted items are here! : http://www.coincommunity.com/forum/...IC_ID=398127
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United States
4654 Posts
 Posted 03/18/2021  8:11 pm  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply

Quote:
found out that my ziplocs had PVC in them.


This is not the case with U.S. manufactured Ziplocs.
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United States
1131 Posts
 Posted 03/18/2021  8:21 pm  Show Profile   Bookmark this reply Add NumisEd to your friends list Get a Link to this Reply
Ziplock bags are definitely not 100% barriers against moisture.
I work at place the manufactures materials that can be extremely hygroscopic. If we would seal these things into ziplock bags the materials would have gone bad within 24 hours to the point there is nothing left but a pile of white dust.
The only way to store things properly, devoid of oxygen and moisture, are evacuated Mylar bags or in an Argon-purged glovebox. The drawbacks are that most people don't have a glovebox at home and Mylar bags are opaque. Can't see your coin.
I think the best and most practical storage solution is to have your coins properly slabbed by NGC or PCGS.
Edited by NumisEd
03/18/2021 8:26 pm
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United States
7138 Posts
 Posted 03/18/2021  9:04 pm  Show Profile   Bookmark this reply Add Earle42 to your friends list Get a Link to this Reply
I know I have read before on this forum that slabs are not airtight. Coins can degrade in them. Have the companies changed this?

I know Air-Tite capsules are marketed as actually being airtight. The capsules are a LOT less expensive than having everything slabbed. En Cap albums are made to hold these capsules.
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 Posted 03/18/2021  9:05 pm  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply

Quote:
materials that can be extremely hygroscopic.


Fortunately our coins are not.

Pillar of the Community
United States
7912 Posts
 Posted 03/19/2021  01:31 am  Show Profile   Check westcoin's eBay Listings Bookmark this reply Add westcoin to your friends list Get a Link to this Reply
I recommend a couple of things to try, archival poly bags would be a possibility, though I too agree that most all food storage products should be safe for coins.

The way the early copper collectors store coins is using 2x2 cotton flannel envelopes which are then inserted into another paper envelope for storage, the cotton has the advantage of not scratching anything, and absorbing moisture. https://www.wizardcoinsupply.com/co...velopes.html These can be hard to find in any real quantity though, and seem to sell out fast.

I have a couple of scientific papers that you may be interested in looking at, they are advanced, but nothing too difficult to understand, and they are about museum conservation products. Both are small PDF's, drop me a PM by clicking on my name if you'd like me to send them on to you via email link.

I'm almost wondering if that isn't mold or spores we are seeing in the bag? That at least could be knocked out with acetone or xylol dip. What types of cleaners or conserving fluids have you tired so far? You mention treating some of the coins in your post.

Another thought is - yes slabs are NOT airtight, and there have been very successful attempts on toning artificially or speeding up toning coins in slabs using zip lock baggies and inert gasses pumped in to them.

If it's a form of corrosion then trying out "Intercept Shield Boxes" or branded coin holders, which may be of use to you. They are their own brand and sell albums, storage boxes coin holders, capsules and albums made using the technology they developed to safeguard against corrosion.

https://www.wizardcoinsupply.com/ Sells the line and Lighthouse Intercept products as well, search for "Intercept Shield" Not sure the availability in Denmark or the EU for you.

While you can no longer order direct, here is their website which has a lot of good information on their unique products. http://www.interceptshield.com/
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Edited by westcoin
03/19/2021 01:37 am
New Member
Denmark
29 Posts
 Posted 03/19/2021  07:18 am  Show Profile   Bookmark this reply Add bw1001 to your friends list Get a Link to this Reply

Quote:
Yes. The problem is that I've never studied this kind of stuff, and it can be very situation-specific.

Here is what I can say about the plastic in ziplock bags (polyethylene)

1. It will let oxygen in through the plastic; it lets in far less water vapor than oxygen.

2. While what @oriole says is true about the polyethylene needing to pass FDA requirements for food contact, this does not mean there are no added chemicals in the bags. There definitely is. Slip agents are substances added in plastics at very low levels (usually less than 1,000 ppm), but they work by migrating to surface of the plastic, which means your coins could be in contact with them. I am relatively certain the plastic in Ziploc bags contain this kind of ingredient. Could they form a whitish deposit on your coin? Yes.
Would they corrode it? I think this is less likely than airborne substances causing the corrosion.


Thanks tdziemia for the explanation. This is what I was looking for on the technical side as it might help me understand what went wrong and when.
I've spent the whole night reading on it (and went on some stupid rabbit hole that made me look for the certifications for the specific kind of ziploc bags) and thanks to you, I am more and more inclined to believe that that's what happened.

I do like how most of the sellers just say that it is safe to store food in them at the end of the description w/o any "ingredients" list, but when you open the certifications you see a few paragraphs that try to limit their liability by pointing at exactly those cases where food could get contaminated

Luckily, from my first assessment (sadly, I have plenty more to go through and it's a tad harsh on my eyes) only a few have the corrosion issue and most have the "white powder" syndrome. Surprisingly, it is the older style of bags (which only God knows what they are made out of, but they are stiffer for sure) that kept them safer than the newer LDPE ones.

My next question would be, if it's not too much to ask, on what should I do next? is there a way to clean them? transferring them would be enough? does the acetone trick work? is acetone safe on 2000 years old coins?
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