Milk Spots- Are They Such a Big Deal?

John and others, I found a site with SEM/Spectro results~ post #26 on this thread
https://www.cointalk.com/threads/need-info-on-mints-annealing-furnaces.262368/page-2#post-2130403

 

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As you are probably aware, the PCGS site is hard to search for specific items. As I understand it the reward was for a practical method to remove the spots without affecting the grade. That is you would need to be able to look at the coin and not see evidence that the spot was there. Since PCGS has eliminated this issue from the guarantee, they may have cooled on it some. In my correspondence with David Hall from 2 years ago this month, he said they were still interested in talking about it. I will try to get more info.

 

Desertgem ... I have the answer. All the information you need to answer this white milk spot dilemma has been presented. It was Bron's thread from Perth, Western Australia that gives you all the data required.

Just you desertgem. How can your prevent silver chloride formation 100% of the time on a 99.999% Ag surface?


John Lorenzo
Numismtist
United States

 

" 1) no chemical attempt to remove them has thus far been successful, and 2) they are nearly always pretty close to round."

1) is not news. 2) is irrelevant.

There are some older discussions to be found on CU forums that are equaly interesting in regards to the chlorides and chemistry being mentioned here too. Thanks for sharing such detailed info here.

 

Thanks. I hope there's something out there we can look at. It would be good if they have something official drafted up that people can use to help define the condition as well as use to discuss the topic when references are made to their initial reward offers. Without something like that or some clearly revoked offer terms, it's not really effective for those interested to keep bringing up the offer.

 

This is not about whether I like your response or not. And I do respect what you have to say, amongst others, discussing this topic. However, you have nothing to back up your claim that the image I posted was not milk spots. You just gave an opinion, which was presented in a totally uninformed manner, that is, without any reason or findings to justify it. With your reputation as a Moderator and very experienced coin person, a lot of people will simply assume you are right, and because that happens a lot around here, others don't seek reasons from you, reasons which you should be prepared to give when you make statements like you did and have someone ask you to explain yourself. But you haven't anything to fall back on other than actually admitting you posted in erroneous fashion or by living up to your endlessly repeated mantra of sharing the information which you suggest would lead one to KNOW the image I posted was not milk spots. What I don't like about your answer, is that you refuse to live up to what you preach or simply admit your fault.

 

Have you notices any milk spots on Chinese Counterfeits?

 

Is that a question or plug?

 

If what you're saying is true and they're both "milk spots" Then why do the ones you describe come off with a dip and the round circular ones stay on . Sounds like two different animals to me .

 

John, at this point I am beginning to doubt that the silver chloride found could initiate a milk spot type of reaction as people have thought. I am thinking that any silver chloride crystals on a coin would sooner rather than later be exposed to light , and the silver chloride molecules would react and initiate a photo reaction to create a molecular size speck of metallic silver ( dark native color). Perhaps if any magnified photos showed a pattern of such on a section of the coin, the over all appearance might of a 'tan coloration', but I would have to be convinced. I think the silver chloride and possibly other silver halides, if found, are outliers; coincidental. I appreciate the insight and photos of the Perth mint people, but I would not currently say I agree on the importance of silver chloride. However, it has helped very much in allowing our visualization of the reaction . To eliminate , I would keep away such things as HCl. Jim

 

Where do you think the silver chloride comes from? It occurs to this observer that the planchets/blanks when put through the annealing process aren't all that well protected from contact with oxygen which allows silver oxide to form on the surface.
It is this oxide formation that the hydrochloric acid wash is intended to remove. It would seem that this washing reaction isn't always driven to completion during the washing process with the net result that it is delayed only to be completed at a later time resulting in the milk spots seen. The other possibility is that the coins that DON'T spot may not have ever had any oxide on them to start with, thus the washing had zero effect on them. Of course without access to the mint's processing details, most of this is educated precision guesswork.

 

Excellent!
Read "Micro-Raman Characteristics of Silver Corrosion Products: Instrumental Set-Up and Reference Database by Irene Martina. It can be googled.
As a few commenters have noticed the spots can appear in the PMD arena after leaving the Mint. Its not so much the acid wash but probably the type of preservative they are putting on at the end of the process. An anti-oxidant coating on the blanks prior to striking or after? Being government (i.e., paperwork - lethargic political machine) and processes taking some time to change they may be using the same type of chemfilm as possibly in the 95%Ag alloys lines?
It's interesting when you look at Martina there are several MORE white compounds in the world of Ag, Cl & S. Namely silver(I) Sulfite: Ag2SO3 and silver(I)Nitrate: AgNO3.
Silver at this purity as you know as with any other coin will pickup chlorine, oxygen and sulfur. The SEM/EDS analyzer confirmed silver(I) Chloride: AgCL but I suspect maybe these others should also be checked being ALSO white powder forms of silver compounds.
As you already know this being a surface phenomenon based on the above using probably an inadequate silver surface anti-oxidant (i.e., similar to why steel is dipped in chromium baths - <BG>; did this myself many years ago to prevent surface corrosion) so to this requires some changes.
It may not be totally corrected since a pilot study here may take time but if they continue to make this pure silver alloy for bullion type accumulators it may be possible in a long term pilot study?
This PCGS question ... it could be like carbon spots on copper proofs. My current cleaning product is strictly for copper verdigris compounds based on fluorocarbon technology (i.e., Original Coin Care) and is for green verdigris with no copper patina change. There is no point answering what can remove these three silver compounds- maybe its just AgCl? Under 5X is there visual surface depressions after removal? <BG>.
As you said ... they just need time ... remember in high urban areas it could be silver sulfite ... in the rural areas predominantly AgCl? Although my studies always show both chlorine and sulfur.

John Lorenzo
Numismatist
United States

 

Sure, those are white -- but silver nitrate will wash away instantly in water, and silver sulfite will dissolve in ammonia or decompose in acid. Since others have said that an ammonia rinse doesn't affect the spots, these seem unlikely.

...Unless, of course, they've actively and visibly etched the surface, and that texture remains after they're gone. That's where we need the SEM imagery, I'd think; scan spotted and unspotted surface regions before and after treatment, and see how each has changed.

Now I really wish my friend still worked at the materials lab...

 

Why would you think that the Mint is putting some kind of coating on the coins after they are struck? What would be the point of that? Assuming that 99.99999% of people are unaware of it, how do you explain the toning that these coins sometimes incur? Wouldn't you have to dip off the coating before you could tone it? As indicated earlier, my examination of the spotting on a single coin from an NGC slab indicated only chlorine was present. If there was a coating there would surely be some carbon, oxygen there too. During the ESCA examination process, the spot was zapped with a beam of argon cations which readily removed the spot.

Look at the physical process of handling a large volume of blanks. This is probably done in bins, totes or baskets. In order to do an effective job of washing and rinsing them they have to be tumbled, agitated, etc. Even plates in a dishwasher need to be separated from each other if you expect them to be cleaned on both sides. A part of the problem might be simply that the wash and rinse aren't making thorough contact with the blanks. This would be akin to a bag of Morgans in storage where the ones next to the bag get toned and the inner protected ones don't.

 

There is always the possibility of chlorine being induced by packaging or even gloves used to handle the finished product. Did the problems start showing up after a change in packaging?

 

When you go back and read old threads on various boards, this seems to have heated up around '06-'07. I hadn't heard of it before then, but then again, I've never seen it at all on my coins. Maybe all my "cow odors" nearby kill it off. For a while, the issue seemed to be mostly in PCGS slabs, and they took a lot of (probably undeserved) heat. When I do see it at shows today, I still see it disproportionately on slabbed coins, regardless of service. Could they somehow be providing a rich environment for the growth of these little buggers? But to be clear, it now shows up even fresh out of mint tubes, too. So let's think - what changed in the range 2006-07, except that more quantity started cranking up? When did the mint run out of the Strategic Silver Reserve and start using purchased pre-done blanks? I think it was well before then.

On those three ESM photos, they all look very different, and the top one looked "biological", like anthrax run amok, speaking of cows.

 

Many polymers contain chloride so in turn most plastics. A change in the process by a vendor maybe? As for those pictures, it will probably turn out to be another monkey virus.

 

I don't have a dog in this fight so I don't really care who is right or wrong. That said, I do love a good argument - as long as it is presented in a logical manner. Krispy, I'm afraid you're falling short in that department. Your arguments seem now to be more from a point of desperation than logic. You demand proof, yet you're not willing (or able) to present any of your own. [BTW, since the marks on the pictures you showed mostly seem to radiate from the devices, rather than at random places over the fields, they look TO ME more like metal flow than anything else (and I'm not going to try to prove or justify that opinion)]

Yet you just gave an uniformed opinion on your markings without justification

But you want us to assume you're right?

What information do you have that would lead us to KNOW that your images ARE milk spots?

And yet you refuse to admit that you may be wrong.

...now, back to the fight argument discussion. Come out of your corners swinging.

 

Good nite sweet prince.........