Need info on mint's annealing furnaces

Discussion in 'Coin Chat' started by desertgem, Apr 15, 2015.

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  1. Yankee42

    Yankee42 Well-Known Member

    Yankee42, Apr 15, 2015
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  3. rlm's cents

    rlm's cents Numismatist

    But silver chloride (the absolute most likely halide) is soluble enough to be washed off with a moderate quantity of water. And, readily decomposes to silver and chlorine in light.
     
    rlm's cents, Apr 15, 2015
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  4. desertgem

    desertgem Senior Errer Collecktor Supporter

    Yankee, thanks for the research. After reading them and also looking over the book on heat annealing, I am starting suspect more the solutions used. The "slippery water" anneal quenching, and the following washing/dryer sequence. I tried to enlarge he sign on the quenching vat, but all it said was that it was a slight irritant. I have out of town company for a week, so I will catch up later. You saved me a lot f time!
     
    desertgem, Apr 15, 2015
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  5. Hommer

    Hommer Curator of Semi Precious Coinage

    @rlm's cents If there is no Chloride or Oxygen used in the annealing process. How could either form if only Hydrogen and Nitrogen are present.
     
    Last edited: Apr 15, 2015
    Hommer, Apr 15, 2015
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  6. desertgem

    desertgem Senior Errer Collecktor Supporter

    desertgem, Apr 15, 2015
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  7. desertgem

    desertgem Senior Errer Collecktor Supporter

    Finally some photo/microscopic material to read.
    http://forums.silverstackers.com/message-755770.html

    first impression is that the first photo ( electron micrograph) looks like a polymer structure with residue of some sort on it. Now we can see some things.
     
    desertgem, Apr 16, 2015
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  8. rlm's cents

    rlm's cents Numismatist

    I did not say there was any. You asked about "silver halide". That would be silver fluoride, silver chloride, silver bromide, silver iodide, or silver astatide. Of those, only silver chloride is remotely common. Hence my answer.

    However, chloride is just about impossible to completely remove from anywhere.
     
    rlm's cents, Apr 16, 2015
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  9. rlm's cents

    rlm's cents Numismatist

    OK professor. Again they are talking about silver chloride. The silver chloride I learned about both decomposes in light and is minutely soluble in water. How can it not be removable and/or develop to begin with.
     
    rlm's cents, Apr 16, 2015
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  10. Hommer

    Hommer Curator of Semi Precious Coinage

    I asked about HAg
     
    Hommer, Apr 16, 2015
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  11. rlm's cents

    rlm's cents Numismatist

    I am sorry. I need to learn how to read.
     
    rlm's cents, Apr 16, 2015
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  12. desertgem

    desertgem Senior Errer Collecktor Supporter

    At this point, I am just gathering information , I have a feeling that any silver chloride might just be incidental and not directly causing the "milk spot". Metallic bonding ( as opposed to ionic or covalent) can be more confusing, as it is not classical chemistry,
     
    desertgem, Apr 16, 2015
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  13. -jeffB

    -jeffB Greshams LEO Supporter

    I'll admit that I don't know much about XRF and other high-tech surface analysis techniques, but surely someone has turned some state-of-the-art tools on these spots. If they really are the result of chemical contamination, it shouldn't be that challenging to figure out what chemical components are there. That would be a good starting point for figuring out how they come into being, if not how to get rid of them.

    I really wish my friend were still working in a material science lab. I know she would've been up for some after-hours tinkering. :(
     
    -jeffB, Apr 16, 2015
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  14. GDJMSP

    GDJMSP Numismatist Moderator

    Yeah, but isn't that what would be expected also ? I mean, nobody sits and watches coins non stop. When they buy a coin they may examine it in minute detail making note of everything there is to note. Same thing when a coin is graded by the TPGs. But then the coin is just put away (raw and/or slabbed), and probably not even looked at all for quite some time, maybe months. But when it is examined again, the spots are there.

    I used to buy rolls of ASE's. I've watched the dealer take them right out of a freshly delivered "green box" and hand them to me. And when I examined the coins at home and put them in individual Air-Tites, sometimes none would have the spots. Other times a couple, or 5 or 10, would have the spots - right out of the mint roll. Yet other times there would be no spots visible, but 2 or 3 months later some of the coins would have spots.

    Now I agree that doesn't help solve the problem or provide any answers. Like you say, much of the needed information is missing. But I suspect just about everybody else's experience is rather similar to mine in regard to the time line of events. And the TPGs have undergone the same kind of thing. They have reported numerous times that when the coins were graded no spots were visible. But later, sometimes months later, the owner of the coin would return the now spotted coin to the TPG wanting then to honor their grade guarantee. And the TPG's have reported that they could not successfully remove the spots.

    Point is, it happens. And it happens just that way. And the fact that there is no rhyme or reason to it is at least part of what makes it so difficult to determine what the details of the events are.

    So short of taking coins with no spots and fresh from mint rolls, laying them out under a constantly running video camera, maybe for months, I know of no way to get the evidence you mention above. And I rather doubt that's ever gonna happen.

    But what about taking a coin that has milk spots. Then taking a sharp instrument and scraping the area with a spot into a container in a lab. Then taking that material and analyzing it. Would that provide any answers ? I would think it would, at least the chemical composition of the material. But would that help ?
     
    GDJMSP, Apr 16, 2015
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  15. BAJJERFAN

    BAJJERFAN Member

    As I understand it a hydrogen/nitrogen mix is used during the annealing process to minimize slag/oxidation. The planchets/blanks are still cleaned after annealing. I suspect that hydrochloric acid is one of the cleaning agents used.
     
    BAJJERFAN, Apr 16, 2015
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  16. Conder101

    Conder101 Numismatist

    I know at one time they used a cream of tatar solution to clean and brighten the silver planchets. Back in 2008 when the "burnished" ASE's first came out there was a lot of discussion about what the mint used for the cleaning/burnishing solution and replies form the mint did list the products. if they were open about it back then I would think they would be willing to give out the information on request today. the problem is it is a commercial product so it probably won't tell you the contents and even if you can find the manufacturer you probably won't get the information.
     
    Conder101, Apr 16, 2015
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  17. Hommer

    Hommer Curator of Semi Precious Coinage

    I'm not so sure of that. From what I remember, HAg can form a metallic bond with pure Ag. Been a while though.
     
    Hommer, Apr 16, 2015
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  18. BAJJERFAN

    BAJJERFAN Member

    There are techniques to analyze the spot on a coin without scraping it off. ESCA/XPS is one that comes to mind. I think the white spots have been pretty much established to be Silver Chloride. Does anyone have any analytical results to suggest that the spots are other than AgCl?
     
    BAJJERFAN, Apr 16, 2015
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  19. john59

    john59 Well-Known Member

    Ammonia solution can dissolve silver residues
     
    john59, Apr 16, 2015
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  20. coloradobryan

    coloradobryan Well-Known Member

    I'm very close to Denver, and could take a tour and ask some questions about the annealing ovens for you Jim.
     
    coloradobryan, Apr 16, 2015
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  21. BAJJERFAN

    BAJJERFAN Member


    But it won't dissolve the milk spots from ASEs. Been there, tried that.
     
    BAJJERFAN, Apr 16, 2015
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