Author Topic: Possible WSOD explanation?  (Read 18466 times)

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Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #30 on: December 03, 2012, 03:14:58 PM »
I've sent back many NGC-graded pandas under their guarantee after they developed the white spots and stains after being encapsulated. I've had this problem most commonly with post-2009 issues, although I've seen it on the majority of years like most of you. I agree that it has gotten far worse in recent years.

After much frustration, I called NGC and spoke with Craig Fiumara directly about what was causing the white spotting and staining on these coins, and why NCS could not take care of them (I actually thought that it could have been improper drying by NCS/NGC). He told me that it is caused from contaminants on the planchets that end up being pressed into the metal during the minting process. He didn't specify what the contaminants were, just that it's from what they use to clean the planchets. Since it is not a substance simply residing on the surface of the coin, there's nothing NCS can do to remove it.

There are definitely many different forms of white spots. The Chinese articles have identified two types and large white spots shown on Maples caused by boric acid, as confirmed by Canadian Mint, is another type. IMO, white spots "on" the surface can be removed if it is done earlier. However, if white spots are related to the impurity of the silver raw material or fine metal dusts left on the die surface during the sand blasting process, the removal of this type spots will be very difficult.

Offline Honus

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Re: Possible WSOD explanation?
« Reply #31 on: December 03, 2012, 03:21:12 PM »
RCM is well known for its problem with having WSODs on silver coins; now China Mint seems to have similar predicament. How about Perth Mint? Does anyone know of any particular issues with Australian silver coins?

I've personally seen them on NGC-graded Kooks and the 2oz Perth Tiger silvers. 
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Offline silverstar1

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Re: Possible WSOD explanation?
« Reply #32 on: December 13, 2012, 09:22:57 PM »
I just noticed this thread .. The white spots have been something of interest to me for quite a while. This is a great article and the first I have seen with a scientific explanation, and that is really the only way to get to the bottom of what is causing these. Through my observations I do also believe there is at least 2 maybe 3 or more different causes of these. On the Chinese coins I have noticed 2, one which is as described above as a very small darker speck (far less than 1mm from what I have seen) with the white spots surrounding that, another is more just round white and even blotchy white spots. With the Canadian coins some are round spots and some also like the Chinese coins are more white blotches . On the Australian Perth mint spots yes some do have them they tend to have more of a bluish hue and I have only observed round ones not the large blotchy types. I really think someone ,a scientist of sorts with the equipment , knowledge and desire would have to do some extensive testing on different types of coins to really find the truth of what is causing these . It is also a thought I have had that some may be caused or enhanced by some reaction of a pollutant in the environment that causes a secondary reaction. I have personally never seen these spots appear later on a coin such as after grading but I have heard others that believe this is the case . Some of that could just be observing them in different light and angles and the spots were always there but they are just now seeing them in a different light or angle. I would have to disagree that there are not many MCC in OMP with spots I have definitely seen many and have seen them from the Australian Perth mint. I think there could be several variables here hopefully we will get closer to some factual explanations.

Offline bonke

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Re: Possible WSOD explanation?
« Reply #33 on: November 02, 2013, 05:44:22 PM »
Thank you for the link.  I read the various explanations with great interest.

Poconopenn - As one of the active participants in the prior discussions, maybe, you will help us understand the present problem.  Recently, Shanghai Mint struck these 1oz and 2oz silver medals.  Possibly, many of the 1oz medals and all of the 2oz medals are showing a white stain on the edges and a white mist on the face of the medals.  Based on these problems, the NGC grades are surprisingly low.  Peter Anthony sees this stain with his medal or medals in the double plastic.  Is this being caused by the inadequate rinse of the acid, the chlorine in the rinse, the saliva of the Mint workers, etc.?  Did the coin forum members (in the prior discussions) actually arrive at a conclusion as to the cause?  Would this apply to these medals when the problem is developing so quickly and within the double plastic?

Mark Bonke

Online fwang2450

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Re: Possible WSOD explanation?
« Reply #34 on: November 02, 2013, 06:48:51 PM »
An old topic revived. I actually uploaded a 2011 article by two engineers from Shenyang Mint in another thread, on the white spots on silver coins. These white spots are AgCl, the Cl part being from "cleaning agents in the production process", most likely the acid used to polish blanks after annealing. If rinsing is not complete, the acid stays on the coins and gets pressed into the coins. When the coins leave the mint, white spots will develop once the acid gets in touch with moisture in the air.

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #35 on: November 02, 2013, 11:33:28 PM »
An old topic revived. I actually uploaded a 2011 article by two engineers from Shenyang Mint in another thread, on the white spots on silver coins.

Please post the link. Thanks.

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #36 on: November 03, 2013, 12:00:24 AM »
Thank you for the link.  I read the various explanations with great interest.

Poconopenn - As one of the active participants in the prior discussions, maybe, you will help us understand the present problem.  Recently, Shanghai Mint struck these 1oz and 2oz silver medals.  Possibly, many of the 1oz medals and all of the 2oz medals are showing a white stain on the edges and a white mist on the face of the medals.  Based on these problems, the NGC grades are surprisingly low.  Peter Anthony sees this stain with his medal or medals in the double plastic.  Is this being caused by the inadequate rinse of the acid, the chlorine in the rinse, the saliva of the Mint workers, etc.?  Did the coin forum members (in the prior discussions) actually arrive at a conclusion as to the cause?  Would this apply to these medals when the problem is developing so quickly and within the double plastic?

Mark Bonke

It is very difficuty to see white spots on a highly frosty surface. Usually, the white spots on mirror surface will affect the grade. The pictures posted by silverybay in other thread does show some "black spots" in forsty area which may affect the grade.

Offline SANDAC

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Re: Possible WSOD explanation?
« Reply #37 on: November 03, 2013, 12:37:29 AM »
Please post the link. Thanks.
I believe this is the link fwang2450 is referring to:
http://china-mint.info/forum/index.php?topic=7823.msg45622#msg45622

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #38 on: November 03, 2013, 08:32:12 PM »
I believe this is the link fwang2450 is referring to:
http://china-mint.info/forum/index.php?topic=7823.msg45622#msg45622


Thanks for posting the link. The article posted by raremedal was incompleted. The completed article can be found in the following link. The website will not allow to download the article.

http://www.docin.com/p-335727916.html (银纪念币表面滋生白斑机理研究, Kang Jin-zhe and Yu Hong, Shenyang Mint Co, Ltd., Corrosion Science and Protection Technology, Vol. 23, No 2, March 2011, Page 197-189)

Summary and comments of the article.

Summary:

1.   The article has further provided the scientific evidences that the formation of white spots can be relatively easy. The white spots can be formed as short as few days after the production of the coin, usually in several months.

2.   The composition of white spots is silver chloride and high humidity is required to promote the formation of silver chloride. The source of chloride, suggested by authors, is from environment pollutants.

3.   The change of minting process of forming mirror surface has caused more and quicker white spots formation. The old method in produce mirror surface was mechanical polish. The current method is via a chemical treatment. Apparently, according to the authors, the chemical treatment produces a rougher surface than mechanical polish. It is known that the moisture can adhere to a rougher surface better than a smooth surface, therefore, the reaction of forming silver chloride film on the silver surface is being accelerated.

4.   The formation of silver chloride film on the silver surface retards the formation of silver sulfide (the usual rainbow toning on silver coin caused by sulfur in the air after aging). The white spots will stay as white and size enlarged with time in a high humanity environment.

Comments:

1.   The article is in consistence with the observations that the earlier MCC do not show white spots as often as MCC produced in the past few years.

2.   IMO, the major source of chloride is from human contact. This article, similar to previous articles (two articles mention by fwang2450 in reply 11 of this thread), has detected significant amount of sodium, carbon and sulfur, the basic element of human fluid, in the white spots. The observation of most white spots developed near the rim and edge  suggests the introduction of sweat (sodium chloride, salt and moisture) during the hand holding inspection of coin by staffs of Mint and grading company.

Online fwang2450

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Re: Possible WSOD explanation?
« Reply #39 on: November 03, 2013, 10:58:35 PM »
I provided the downloaded article in that thread, but if anyone missed it, I am uploading it again.

I don't believe that human contact can result in such wide-spread occurrence of white spots on recent coins. In this article, two causes are given: chemical polishing, which does not involve chlorine; and cleaning agents, which do contain chlorine. I guess that the cleaning agents are used to clean blanks after annealing. When rinsing is incomplete, the cleaning agents will remain and lead to white spots.

Offline poconopenn

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Re: Possible WSOD explanation?
« Reply #40 on: November 04, 2013, 09:05:27 PM »


I don't believe that human contact can result in such wide-spread occurrence of white spots on recent coins. In this article, two causes are given: chemical polishing, which does not involve chlorine; and cleaning agents, which do contain chlorine. I guess that the cleaning agents are used to clean blanks after annealing. When rinsing is incomplete, the cleaning agents will remain and lead to white spots.

It is my understanding that no chloride compound is being using in the minting process, including blank preparation. The only place mentioned the potential source of chloride in this article is the cleaning solution used to keep the plant in a proper production environment(生产环境). In other words, the cleaning solution containing chloride is for housekeep purpose, not used in production process. In the conclusion of this article, the authors made the recommendation to dry the blanks longer to make sure that no trace of moisture left on the surface of the blanks, since chemical treated silver surface produces a rougher texture, therefore, more moisture will adhere to the surface.

The authors, for unknown reason, did not consider the effects of sodium, which is a highly corrosive chemical for most metals. The significant amount of sodium was found in the white spots, not only in this article, but also in previous two articles. The obvious source of sodium and chloride is from salt in the human fluid which can be introduced to the coin surface during the inspection. China Mint has claimed that 30% of coin produced were inspected manually.

Definitions of 生产环境:

http://baike.baidu.com/link?url=CuYxhZPpUCEs8TcGo-eRobqAK7nrkwyh0A2Qz3aac4N24boiYjV3yn9ARooXWFcLPHiYzLRFcU1lTDtnozNiNq


Online fwang2450

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Re: Possible WSOD explanation?
« Reply #41 on: November 04, 2013, 09:48:08 PM »
It is my understanding that no chloride compound is being using in the minting process, including blank preparation. The only place mentioned the potential source of chloride in this article is the cleaning solution used to keep the plant in a proper production environment(生产环境). In other words, the cleaning solution containing chloride is for housekeep purpose, not used in production process. In the conclusion of this article, the authors made the recommendation to dry the blanks longer to make sure that no trace of moisture left on the surface of the blanks, since chemical treated silver surface produces a rougher texture, therefore, more moisture will adhere to the surface.

The authors, for unknown reason, did not consider the effects of sodium, which is a highly corrosive chemical for most metals. The significant amount of sodium was found in the white spots, not only in this article, but also in previous two articles. The obvious source of sodium and chloride is from salt in the human fluid which can be introduced to the coin surface during the inspection. China Mint has claimed that 30% of coin produced were inspected manually.

Definitions of 生产环境:

http://baike.baidu.com/link?url=CuYxhZPpUCEs8TcGo-eRobqAK7nrkwyh0A2Qz3aac4N24boiYjV3yn9ARooXWFcLPHiYzLRFcU1lTDtnozNiNq


My understanding of 生产环境 is different. I worked in a factory for more than 4 years. 生产环境 can mean the environment, or the entire production process. But if you have evidence that no chlorine products are used in acid cleaning (I have heard of nitric acid and sulfuric acid), my guess would be wrong.

Offline poconopenn

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Online fwang2450

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Re: Possible WSOD explanation?
« Reply #43 on: March 23, 2016, 10:04:20 PM »
Thanks for sharing! But I wonder whether acetone will do the trick.

Offline KeepOnTrying!

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Re: Possible WSOD explanation?
« Reply #44 on: March 23, 2016, 10:38:38 PM »
Thanks for sharing! But I wonder whether acetone will do the trick.

Do you know of something else that will get rid of or reduce the density of the white spots? NCS is not going to share their secrets. So far they don't claim to get rid of white spots but that may be because they cannot guarantee 100% spot removal. I am interested in this issue!

Thanks.

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