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How To Slow The Degradation Of A Worsening Patina

 
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Pillar of the Community
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 Posted 09/15/2021  10:07 pm Show Profile   Bookmark this topic Add mdpmedia to your friends list Get a Link to this Message
What do you do when you see the horrible effects that verdigris and/or rust can have on your coins?

Do you ever test the atmosphere of your coin's storage container?

What element is THE most essential component to initiating degradative chemical reactions leading to the formation of damaging products to a surface of a coin?

Pillar of the Community
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 Posted 09/15/2021  10:15 pm  Show Profile   Bookmark this reply Add mdpmedia to your friends list Get a Link to this Reply
a picture is worth 10,000 words...





I asked myself these questions and placed a $1 dessicant inside of a safe and waited for three months. The two shots here show how drastically the amount of water had accumulated inside of this dessicant while residing inside of a 'closed' safe.
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61493 Posts
 Posted 09/15/2021  10:17 pm  Show Profile   Bookmark this reply Add Coinfrog to your friends list Get a Link to this Reply
There is no simple answer to your question.

Please show us images to start a conversation.
Pillar of the Community
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 Posted 09/15/2021  10:22 pm  Show Profile   Bookmark this reply Add mdpmedia to your friends list Get a Link to this Reply
Virtually every chemical reaction must have H2O to begin and come to an end.

The recommend Rh for coin storage is ideally about 30%. Anything lower is harder to achieve but not impossible.

IMO it is unnecessary to measure Rh unless you want to purchase more meters which can be avoided by simply observing and changing out the dessicant every couple of months or as needed.
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 Posted 09/15/2021  10:29 pm  Show Profile   Bookmark this reply Add mdpmedia to your friends list Get a Link to this Reply

Quote:
...show us images


Either this question was posted before I uploaded the two desicants or it refers to coins' before and after status.

If it is the later, the only point being made here is that destructive chemical reactions will occur significantly slower or not at all without the presence of water...
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Australia
19084 Posts
 Posted 09/16/2021  02:46 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
Beautiful rainbow toning on a silver coin is delicate and unstable over the long term, and it's deterioration cannot be reversed -
much like feminine pulchtitude.

Unlike the feminine version, it can be however be almost be completely arrested by housing the coin in a completely air tight environment. A screw seal acrylic capsule of appropriate diameter would be the best solution to this problem.

Can't do that with the feminine version. She might have you arrested first!
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 Posted 09/16/2021  07:38 am  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
Yes, it's a good reminder that most corrosion reactions need water present. So using dessicants can slow whatever reactions take place.

In many homes, it's less of an issue due to seasonal fluctuations in RH (indoor air is pretty dry in the cold months here in the midwest) and modern HVAC systems. If I lived in the southeast and didn't have air conditioning, I would certainly consider using dessicants where my coins are stored.

Or moving ...
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 Posted 09/16/2021  07:48 am  Show Profile   Bookmark this reply Add just carl to your friends list Get a Link to this Reply
Keep moisture away from coins. I simply put coins in Plastic Zip lock bags.
just carl
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 Posted 09/16/2021  08:56 am  Show Profile   Bookmark this reply Add kanga to your friends list Get a Link to this Reply

Quote:
Keep moisture away from coins. I simply put coins in Plastic Zip lock bags.


#1 Moisture is definitely the most damaging factor. Use desiccants.
#2 Keep the temperature as constant as reasonably possible.

And I'm not so sure about Plastic Zip lock bags.
They may contain PVC (plastic softener).
Non-PVC flips or 2x2's would be preferable.
Capital Plastics holders are very good but very expensive.
Describe it as if there were no picture.
Picture it as if there were no description.
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 Posted 09/16/2021  11:17 am  Show Profile   Bookmark this reply Add jbuck to your friends list Get a Link to this Reply

Quote:
And I'm not so sure about Plastic Zip lock bags. They may contain PVC (plastic softener).
They do not. They are made with polyethylene. I would only use the clear ones though to avoid issues with dyes.

And to be clear, PVC is a rigid plastic. It is the softeners (plasticizers) added to it that cause problems for coins as it leaches out.
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 Posted 09/16/2021  11:57 am  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
Correct.
And polyethylene is a pretty good moisture barrier, but it does allow some in.
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 Posted 09/16/2021  8:07 pm  Show Profile   Bookmark this reply Add Sap to your friends list Get a Link to this Reply
The other chemical to avoid is sulfur. Silver, in particular, reacts with sulfur-containing chemicals in the atmosphere to produce silver sulfide, which is black, and it does not need moisture in the air to form. This is what "tarnish" and "toning" on silver coins is made of. It is also why you get a "rotten eggs smell" when you clean tarnished silver coins with silver dip, as the silver sulfide reacts to form hydrogen sulfide gas.

Sulfur can be found in numerous everyday items. Virtually every kind of "rubber" has sulfur in it, because it's the sulfur cross-links that make a polymer "rubbery". Paper and cardboard, particularly if it's coloured, often has sulfur compounds in it (hence the oft-heard claims of Taco Bell napkins being good for "re-toning" silver coins). And of course sulfur could be in the air to begin with; ambient sulfur dioxide is less common nowadays with anti-acid-rain pollution control laws put in place way back in the 1980s, but if there's a kitchen in the house where garlic and other aromatic foods are being prepared, there'll be plenty of sulfur put up into the air from that source.

Sulfur will also cause coins of other metals to turn black - particularly copper and bronze.
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
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 Posted 09/16/2021  8:46 pm  Show Profile   Bookmark this reply Add tdziemia to your friends list Get a Link to this Reply
The silver sulfide reaction does require water:

The main product of silver tarnishing is silver sulphide. The reaction mechanisms are:
8Ag + 4HS- <---> 4Ag2S + 2H2 + 4e-
02 + 2H2O + 4e- <---> 4OH-
The first reaction is believed to occur in a thin film of water on the silver surface. In dry air, tarnishing does not take place
.
/www.vam.ac.uk/content/journals/conservation-journal/issue-18/tarnishing-of-silver-a-short-review/

The HS- ion results from hydrogen sulfide dissolving in water: H2S + H2O <-> HS- + H3O+
Edited by tdziemia
09/16/2021 8:50 pm
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