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Thread: Silver Metal Turning Black after Putting a Torch to it?

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  1. #1
    Finding the Gold

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    Question Silver Metal Turning Black after Putting a Torch to it?

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    Hey guys, I had found this 2 gram piece of silver metal while prospecting, was trying to find out what it was. One guy said he thought it was gold covered in mercury, but I put a torch to it and it got cherry red and instead of turning gold it turned black afterwards. Does anyone have any idea what type of metal would do that? Lead, silver, nickel?

  2. #2
    us
    May 2014
    AZ
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    Are you sure that it is metal? That said, Silver tarnishes black so could be? Lay a file to a sharp corner or maybe see if a little silver polish brings back a distinct silver color which the original photo does not show. Is it attracted to a strong magnet? If it is magnetic it could be platinum.

    Good luck.
    Last edited by arizau; Apr 22, 2019 at 11:45 AM.
    If it can't be grown, it must be mined!

  3. #3
    Charter Member

    Sep 2014
    Midwest, North of 36°60'
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    You might toss it into a graduated cylinder to get the volume of the piece which along with the mass of the peice would give you it's density. Density could be a major clue. Gold and platinum are around 19-21 grams per a cubic centimeter. Pure silver has a density of exactly 10.5 g/cc. It is probably not pure so the density would be lower. Base metals have much lower densities than gold, copper is around 7.5g/cc.

    Also what kind of torch did you use? Propane won't touch platinum and it is a $&@!+ to melt platinum with acetylene.
    Jim in Idaho likes this.
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  4. #4
    Finding the Gold

    Apr 2019
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    28 times
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    Quote Originally Posted by arizau View Post
    Are you sure that it is metal? That said, Silver tarnishes black so could be? Lay a file to a sharp corner or maybe see if a little silver polish brings back a distinct silver color which the original photo does not show. Is it attracted to a strong magnet? If it is magnetic it could be platinum.

    Good luck.
    Yea it is metal. It was slightly magnetic in certain areas before I put a torch to it, but then after the torch it is no longer magnetic. Weird! I have it soaking in vinegar right now to see if it takes the black away.

  5. #5
    Finding the Gold

    Apr 2019
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    28 times
    Prospecting
    Quote Originally Posted by Duckshot View Post
    You might toss it into a graduated cylinder to get the volume of the piece which along with the mass of the peice would give you it's density. Density could be a major clue. Gold and platinum are around 19-21 grams per a cubic centimeter. Pure silver has a density of exactly 10.5 g/cc. It is probably not pure so the density would be lower. Base metals have much lower densities than gold, copper is around 7.5g/cc.

    Also what kind of torch did you use? Propane won't touch platinum and it is a $&@!+ to melt platinum with acetylene.
    Those are some really good suggestions. I thought about buying a test kit. It was a propane torch. I had it on it for a while, just got cherry red, didn't melt or anything. I do think it might have had some iron on it before I torched it because it was slightly magnetic before I torched it and had a slight bit of rust in one spot. But after I torched it has no magnetic properties at all now and no signs of iron at all on it anymore. You can scratch it and see silver underneath the black. It would be cool if it was platinum. I might have to try your suggestions to get a better guess or buy a test kit.

  6. #6
    us
    Jan 2019
    Maine
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    You would have to get the nugget pretty hot for a long time with a propane torch to melt it even if it was silver. You would also need an oxidizing flame.

    Silver melts about 1750 degrees, but could be higher if it has impurities in it. "Red Hot" is about 1250 degrees, so you would only be 75% to the melting point….but I was not there either, and some of that is subjective.

    The black is misleading because it could be tarnish from silver getting near its melting point, or it could be from the hydrocarbons burning off the propane gas.

    The magnetic aspect you speak of has no real bearing. My magnetic thermometer on my woodstove falls off when it reaches 800 degrees. That is typical. But it cannot be melanite because that is strongly magnetic before heating, and while ilmenite has a weak magnetic attraction like you describe, it is black in color like melanite.

    It could be a PGM, and if it is, it is a real nice one!
    Duckshot likes this.

  7. #7
    us
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    Anyhow, please be very cautious heating unknown materials. If this carries mercury or cadmium, the vapors are highly toxic.

  8. #8
    Make America Great Again

    Apr 2013
    Oregon
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    could be a piece of Babbitt or other mix of material that was melted at one point.
    file a spot to do a streak test on a piece of unglazed porcelain could give some indication.
    https://geology.com/minerals/streak-test.shtml
    russau and Jim in Idaho like this.
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  9. #9
    Finding the Gold

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    Quote Originally Posted by OreCart View Post
    You would have to get the nugget pretty hot for a long time with a propane torch to melt it even if it was silver. You would also need an oxidizing flame.

    Silver melts about 1750 degrees, but could be higher if it has impurities in it. "Red Hot" is about 1250 degrees, so you would only be 75% to the melting point….but I was not there either, and some of that is subjective.

    The black is misleading because it could be tarnish from silver getting near its melting point, or it could be from the hydrocarbons burning off the propane gas.

    The magnetic aspect you speak of has no real bearing. My magnetic thermometer on my woodstove falls off when it reaches 800 degrees. That is typical. But it cannot be melanite because that is strongly magnetic before heating, and while ilmenite has a weak magnetic attraction like you describe, it is black in color like melanite.

    It could be a PGM, and if it is, it is a real nice one!
    Some good info here. Thanks for the tips and info. I thought about the hydrocarbons too. Was wondering about that.

  10. #10
    Finding the Gold

    Apr 2019
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    28 times
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    Quote Originally Posted by placertogo View Post
    Anyhow, please be very cautious heating unknown materials. If this carries mercury or cadmium, the vapors are highly toxic.
    Thanks you are right, I had that thoughts too about the vapors. I ended up wearing a vapor paint mask, went out in the middle of no where so I wouldn't be putting the vapors near anyone and also stood upwind from it when I was torching it.

  11. #11
    Finding the Gold

    Apr 2019
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    28 times
    Prospecting
    Quote Originally Posted by winners58 View Post
    could be a piece of Babbitt or other mix of material that was melted at one point.
    file a spot to do a streak test on a piece of unglazed porcelain could give some indication.
    https://geology.com/minerals/streak-test.shtml
    yea good idea. I was thinking about buying a streak testing kit, at least I could narrow down what it is not if it has a silver test. I guess I could just do a regular streak test though. good thinking.

  12. #12
    us
    Jan 2019
    Maine
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    422 times
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    Quote Originally Posted by CDCGoldProspecting View Post
    yea good idea. I was thinking about buying a streak testing kit, at least I could narrow down what it is not if it has a silver test. I guess I could just do a regular streak test though. good thinking.
    You could take it to a scrap yard and have them zap it with a XRF hand held scanner. Just about every scrap yard has one now to identify materials. It does not really work well on testing potential ore as there are too many variable involved, but on a nugget it would.

    Even if you paid them a few bucks "for their time", it might be worth it, and cheaper then buying items to identify it at home (though having items at home is always good for the next iridium nugget you find (teasing).

    (I assume you do not have $15,000 to spend on a xrf scanner, but if you do, then disregard this message.) (LOL)

  13. #13

    May 2005
    St. Louis, missouri
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    Quote Originally Posted by CDCGoldProspecting View Post
    yea good idea. I was thinking about buying a streak testing kit, at least I could narrow down what it is not if it has a silver test. I guess I could just do a regular streak test though. good thinking.
    You can make your own streak test kit by using the back of a piece of unglazed tile .

  14. #14
    us
    May 2014
    AZ
    Sweep Jig, Whippet Dry Washer, Lobo ST, 1/2 width 2 tray Gold Cube, numerous pans, rocker box, and /home made fluid bed and stream sluices.
    2,006
    2899 times
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    Quote Originally Posted by russau View Post
    You can make your own streak test kit by using the back of a piece of unglazed tile .
    Or the underside of a porcelain toilet tank lid.
    If it can't be grown, it must be mined!

  15. #15
    Finding the Gold

    Apr 2019
    25
    28 times
    Prospecting
    Quote Originally Posted by OreCart View Post
    You could take it to a scrap yard and have them zap it with a XRF hand held scanner. Just about every scrap yard has one now to identify materials. It does not really work well on testing potential ore as there are too many variable involved, but on a nugget it would.

    Even if you paid them a few bucks "for their time", it might be worth it, and cheaper then buying items to identify it at home (though having items at home is always good for the next iridium nugget you find (teasing).

    (I assume you do not have $15,000 to spend on a xrf scanner, but if you do, then disregard this message.) (LOL)
    haha nope don't have $15,000 I want to spend on that. That is a great idea though. I might call a couple around here and see if they would do it for me!

 

 
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