AT MS70 vs NT on Copper Coins
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When looking at US copper from the last two hundred years are there markers that indicate a coin has had MS70 applied vs. natural toning? What should one look for that will indicate AT toning from a product like MS70?

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It has been my understanding that Mint State copper turns blue when it is treated with this stuff. This is the reason why that color has become the grounds for a "details" grade in recent years.

 

I might be ignorant on this point because I avoid messing with coins as much as possible. I have not cared for the resulting look of silver coins that have been treated with MS-70, and therefore I have a negative attitude toward the stuff.

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Go to your local hardware store and buy a small sheet of copper. Cut it into strips and dip one in your preferred product, clean another with acid and then dip, and keep another as it. Let them age and tell us what you observed.

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Go to your local hardware store and buy a small sheet of copper. Cut it into strips and dip one in your preferred product, clean another with acid and then dip, and keep another as it. Let them age and tell us what you observed.

 

Copper coins should be left alone PERIOD. You will almost certainly not improve them by messing with them.

 

The only time when you might consider doing something is when there is active corrosion. My action would be to avoid buying it, but I suppose if you are an expert coin doctor you might do something then, and that case I'd probably support your decision.

 

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MS70 does nothing to red copper. However, if the copper has turned brown, it will turn the coin blue. Many times, such coins make it through the services with a problem free grade. This should help explain why copper coins with blue and purple color are typically given a BN designation.

 

I recommend leaving copper alone, as Bill has already said. It is an unstable metal after it has been treated.

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MS70 can react with some copper and give it a blue appearance. It is not accurate that it only happens on BN copper. I have had red copper react. I've also had it turn copper ugly pink and others gray. It's a gamble. Most times it does nothing other than clean the coin.

 

NGC seems to be OK with blue copper. PCGS is hit and miss, but I'd say more often than not they will allow it in a problem free holder. Blue copper is not only market acceptable, it is sought after.

 

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Blue copper is not only market acceptable, it is sought after.

 

As long as collectors are willing to buy blue copper the lustrous pieces will be market acceptable. It is a another area the TPGS can make money and keep collectors happy.

 

Also I have searched the forums and asked several experts in copper about the stability of blue toned copper and I have found no reason to believe it is not. I had many coins that people felt were MS70 treated and saw no changes in 5 years. I have also seen many of them cross to PCGS.

 

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This topic has been discussed regularly and in some depth many times here (and elsewhere).

 

Just a few of the threads from here:

 

MS70 reacts with oxidated copper surfaces. (July 2006)

 

I processed TEN copper coins with MS-70 last night - SEE THE RESULTS! (August 2006)

 

A quick MS70 experiment for those that don't think it turns copper blue (August 2008)

 

MS70 causes blue toning on copper? (December 2010)

 

MS70 conservation on copper - what does it do? Final summary posted!! (February 2011)

 

Keeping MS70 'Coin Cleaner' in Perspective (March 2011)

 

A little fun with MS70 and copper (December 2012)

 

Does this look original to you? (April 2013)

 

Is the MS70 look stable (November 2014)

 

 

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