Author Topic: Possible WSOD explanation?  (Read 17236 times)

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Offline Panda Halves

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Possible WSOD explanation?
« on: August 06, 2011, 08:13:34 PM »
Are water contaminants the source of WSOD(White Spots of DEATH!) instead of packaging?

“The most common pollutants in Shanghai drinking water are high levels of chlorine, bacteria, and lead and toxic heavy metals.  Shanghai’s water authorities have publicly acknowledged that tap water potability is compromised largely by secondary contamination from old piping.  The heavy use of chlorine is necessary for disinfection, but is also unhealthy and can create carcinogenic byproducts.”

Source: http://www.purelivingchina.com/learning-center/water-quality/

If the water in China has this many pollutants then is it possible that these pollutants are getting deposited on the surface of coins when either the blank planchets are quenched or washed?  Perhaps the reason latter date coins seem to be more and more susceptible to WSOD is that the levels of chlorine, heavy metals, and other contaminants have risen in the water supply of the cities where the coins are being minted. This could explain why, although the packaging seems to be improved, the WSOD phenomenon seems to be actually getting worse. Many 2011 Aviation Industry silver pandas I’ve seen are plagued with spots straight from the mint. Perhaps the coins are washed and dried but the contaminants in the water supply are being deposited on the coin then the coin along with the contaminants is “sealed.” It wouldn’t matter what this sealed plastic holder is made of if the surface of the coin is contaminated. As population levels have risen in industrial areas more contaminants have entered the water supply, along with more unwanted contaminants, additives such as chlorine are added to the water in attempt to purify it for drinking. Both additives and contaminants are not good for coins. This is of course… all speculation but is it at least plausible? Thoughts?

Offline badon

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Re: Possible WSOD explanation?
« Reply #1 on: August 06, 2011, 08:35:51 PM »
This is very possible. My analysis of the issue determined that the white spots were caused by chlorine. I've made a few detailed posts on LBC and CCF describing how the reaction works, how to prevent it, and possibly how to reverse it.

I don't have them handy in front of me though, so you'll have to do a search to find them.

Offline adamc4

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Re: Possible WSOD explanation?
« Reply #2 on: August 06, 2011, 08:49:58 PM »
My question is: even after NCS + NGC can white spots 1) appear 2) get worse and grow or 3) be "frozen" in their current state?

Offline Panda Halves

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Re: Possible WSOD explanation?
« Reply #3 on: August 06, 2011, 08:57:25 PM »
Badon, do you think the chlorine could possibly come from the over-chlorinated water supply vice outgassing?

Offline badon

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Re: Possible WSOD explanation?
« Reply #4 on: August 06, 2011, 09:11:05 PM »
My question is: even after NCS + NGC can white spots 1) appear 2) get worse and grow or 3) be "frozen" in their current state?

1. Yes, especially if the reaction has already started before the conservation process, which can't always been seen visually.

2. Get worse, yes. Grow, no. Although it is theoretically possible for a properly conserved coin to get worse over time, I haven't seen it yet. The conserved coins I have seen with white spots seem to be much more stable over time, since most of the chlorine got rinsed away in the conservation process. The only way to make it worse in theory is probably repeated cyclical exposure to humidity, UV light (sunlight), or both.

3. This is what SEEMS to be the case so far for white spots that have been conserved. The conservation process seems to stop the spot reaction process by removing the free chlorine. Once that's gone, all that's left is the chlorine that's already reacted with the silver to produce AgCl molecules. That just seems to sit there and do nothing, although I do think it's possible for it to continue damaging the coin. I might try to do some tests someday to see what happens. I have owned a coin that was conserved after spots formed, and I noticed no changes after 5 years. Conservation seems to have greatly improved the coin's appearance, and stopped the reaction.

Badon, do you think the chlorine could possibly come from the over-chlorinated water supply vice outgassing?

White spots never come from outgassing, or anything else related to the packaging. White spots come from a very simple chlorine reaction, and they always have the bulbous shape of water stains. I think it is very likely that it comes from some kind of water - maybe the drinking water supply, or maybe a diluted hydrochloric acid solution (to clean the planchets). Or both!

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #5 on: August 06, 2011, 10:32:18 PM »
WSOD also show up in eagles and maples. This is not just the problem of silver panda. It has to be related to the production of  planchets, an unknown impurity in the planchets which may be oxidized to form a white spot. Silver is known to be the by product of zinc, copper and gold mining. If I have to take a guess, the zinc may be the one, since zinc oxide is a white color powder.

Offline badon

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Re: Possible WSOD explanation?
« Reply #6 on: August 07, 2011, 02:15:56 AM »
ZnO is too white. WSoD look a little bit darker than the bright white ZnO, which is the main ingredient in powerful sunblock lotions. Also, the "stain" patterns do not match what impurities normally look like.

http://en.wikipedia.org/wiki/Zinc_oxide
http://en.wikipedia.org/wiki/Silver_chloride

I  have seen impurities that look like they might be a bit of zinc in the silver, so it is an interesting possibility in some cases. In the case of WSoD, the reaction rate is too fast. Plus, zinc isn't very prone to oxidation, that's why it's used as the coating for galvanized steel. It oxidizes less readily than iron does.

Within a coin's original seal, I would expect zinc to remain pristine for a very long time. Maybe there would be a gap in the toning on a silver coin, where the zinc didn't oxidize, but the silver did.

It would be interesting to test the white spot to find out for sure what it is.

Offline Panda Halves

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Re: Possible WSOD explanation?
« Reply #7 on: August 07, 2011, 08:04:37 AM »
Maybe someone with connections should find the most spot covered common silver coin and send it to a university chemistry laboratory for analysis.
Analyzing Chinese silver and gold coin surface contaminants make a good research paper for some student.
If the impurities are from a water source then it would make sense that different mints would be more likely to develop the spots than others, especially since Shanghai seems to have such hard/chlorinated water. Scientificall proving what they are would make the case for conservation even stronger.

Offline badon

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Re: Possible WSOD explanation?
« Reply #8 on: August 07, 2011, 11:33:33 AM »
I've found evidence that they're from a liquid or water source. They ALWAYS have a smooth border with a bulbous shape. Water always has some dust, debris, or dissolved minerals in it, just like hard water. As the drop of water evaporates, the drop shrinks, but it does not leave behind the dust etc that is in it until it shrinks to a speck and evaporates completely.

All round WSoD's have a speck of dirt right at their center, just like I described above. Knowing that they come from water rules out a lot of possibilities, including the ZnO hypothesis. The most likely possibility is AgCl. I cannot think of any other thing it could be.

Still, it would be good to confirm it.

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #9 on: August 07, 2011, 02:04:39 PM »
Please note that de-ionized water is used in cleaning the dies, planchets and coins in Mints. This is a standard procedure used by all Mints. The hardness and chlorine gas in the water are not the issue.

Offline badon

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Re: Possible WSOD explanation?
« Reply #10 on: August 07, 2011, 02:13:08 PM »
Possibly there was a problem in the quality of the rinse. The planchets were probably pickled in an acid bath to clean them, and then they were rinsed. If the rinsing was incomplete, diluted acid would dry on the surface of the planchet. This explains why exposure to humidity causes struck coins to develop spots decades later.

Offline fwang2450

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Re: Possible WSOD explanation?
« Reply #11 on: November 29, 2012, 05:51:30 PM »
It turned out that Shanghai Mint did their own research long time ago, in 2002. Attached are two articles from Shanghai Mint (in Chinese, one of them published in a journal) discussing white spots on silver coins, method to remove them and how to prevent them. Mr. Feng (RAREMEDAL) referred to the articles in his post on coin oxidation: http://bbs.jibi.net/dispbbs.asp?boardid=176&Id=206388&page=4

The article in the PDF format confirms that the white stuff is caused by chlorine, and that normal acid bath cannot remove it. They suggested using chromium trioxide to form a film, then removing the film with ammonia and using sulfuric acid for polishing (?) as a way to get rid of the white spots. I guess this can only be done by professionals, like those at NCS.

Interestingly, the article does not mention where the chlorine came from, but water was mentioned as one of the possible causes.

The article in the Word format mentions iron in small white spots (about 1mm). In the center there is a little black dot, which turns out to be iron. It interacts with chlorine to form little white spots.

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #12 on: December 02, 2012, 01:53:31 AM »
Fwang2450, thanks for posting this very interesting article.

The authors observed a very small dark particle under the white film in their study. This is a very significant finding. Furthermore, they suggest the dark particle is related to iron as impurity introduced during the minting process.

The results of instrumentation of white spots reveal unusual amount of chlorine, oxygen and sodium, while the dark spots has a detectable amount of iron. The authors did not provide a clear interpretation of the chemical mechanism of the formation of the white film but simply suggested the silver surface containing iron might be corroded by chlorine and sodium which caused the discoloration of the surrounded area.

Here are some facts which authors of this article may not know.

Very few double sealed mint packaged coins develop white spot. Practically, all coins made with silver purity in 90-92.5% do not develop white spots. NGC and PCGS encased coins can develop white spot inside the holder. The white spots also show up in eagle and maple, but not in any silver coin made by Australia Mint.

IMO, the iron is not introduced during the minting process, but from the impurity of the silver raw material. I also believe the sources of chlorine and sodium is from human contact such as sweat or mist from breath. Both sweat and breath contain sodium chloride (salt) which can be acted as corrosive agent and react to iron to form ferrous chloride which is white in powder form.

Offline dynamike51

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Re: Possible WSOD explanation?
« Reply #13 on: December 02, 2012, 02:19:47 AM »

Very few double sealed mint packaged coins develop white spot. Practically, all coins made with silver purity in 90-92.5% do not develop white spots. NGC and PCGS encased coins can develop white spot inside the holder. The white spots also show up in eagle and maple, but not in any silver coin made by Australia Mint.


poconopenn:

According to your post, is it correct to assume whatever is causing the white spots (be it the human breath or sweat) occurs during the NCS/NGC/PCGS process ?
« Last Edit: December 02, 2012, 02:28:52 AM by dynamike51 »

Offline fwang2450

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Re: Possible WSOD explanation?
« Reply #14 on: December 02, 2012, 02:32:15 PM »
Fwang2450, thanks for posting this very interesting article.

The authors observed a very small dark particle under the white film in their study. This is a very significant finding. Furthermore, they suggest the dark particle is related to iron as impurity introduced during the minting process.

The results of instrumentation of white spots reveal unusual amount of chlorine, oxygen and sodium, while the dark spots has a detectable amount of iron. The authors did not provide a clear interpretation of the chemical mechanism of the formation of the white film but simply suggested the silver surface containing iron might be corroded by chlorine and sodium which caused the discoloration of the surrounded area.

Here are some facts which authors of this article may not know.

Very few double sealed mint packaged coins develop white spot. Practically, all coins made with silver purity in 90-92.5% do not develop white spots. NGC and PCGS encased coins can develop white spot inside the holder. The white spots also show up in eagle and maple, but not in any silver coin made by Australia Mint.

IMO, the iron is not introduced during the minting process, but from the impurity of the silver raw material. I also believe the sources of chlorine and sodium is from human contact such as sweat or mist from breath. Both sweat and breath contain sodium chloride (salt) which can be acted as corrosive agent and react to iron to form ferrous chloride which is white in powder form.

poconopenn:

There are two articles. The Word article talks about 1mm white spots, which has some iron particles in the center. I don't believe this is the kind of white spots we are talking about. The white spots that catch most attention are much bigger.

The article does not specifically say the iron particle is introduced in the minting process, which is 加工 in their terminology. Instead, the authors claim that the iron is added in the production of the silver base material. That is why the number one preventive measure proposed is "enhance the quality of the base material."

In the PDF file, there is no mention of iron as the cause of the white spots, but the authors do provide an analysis of the chemical process which lead to the white spots.

About the environment of white spot formation, I have read that a large number of the new Wutai Mountain silver coins develop white spots when double sealed. Also, I have a 15g Compass silver coin with two white spots. Its fineness is 90%. Of course these are just personal observations. More input is needed to validate the exact conditions for the development of white spots.

Now that Shanghai Mint knows the cause of white spots (chlorine), and the proposed solutions from these authors, and yet white spots still appear in force on their coins (Wutai was minted by Shanghai Mint and Shenzhen Mint), the only explanation is the cost or process. Maybe they are just using untreated tap water which is rich in chlorine instead of deionized water. Or they use hydrochloric acid to clean the planchets without complete rincing. (Mr. Feng cited pugent gas in the mintng process.) It is really puzzling that they pinned down the cause 10 years ago and are still producing coins with white spots, which directly impact their sales.

I have not personally seen white spots on American or Canadian silver coins. But from what I read, the white fog on silver Maples is different in shape from the WSOD. Also, the Canadian Mint acknowledged that the white fog was caused by boric acid remnant, but they have done nothing about it as silver Maples are just bullion coins. There are videos on Youtube on how to remove the white fog on silver Maples.