Red Spot Gone

[Serendipity]

It’s important before I begin this post that the general advice professional numismatists give about cleaning coins is don’t. Many collectors will not buy a coin which has been cleaned and restored to its original pristine condition because of their familiarity with toned coins. Chards has a very instructive article on the subject: https://www.chards.co.uk/blog/coin-toning/232.

Anybody who has been collecting gold coins for a while now is familiar with the dreaded “red spot.” These marks are also known as “copper spots” which pretty much sums up their nature because they are ultimately caused by tiny specs of copper (part of the 0.0001 of the item in 0.9999 purity gold) that are exposed at the surface of the item and react with air. 

I recently bought a 24-karat gold bullion coin, a 2019 1oz American Buffalo, and noticed a visible red spot above the American Indian’s eye on the obverse like he had been wounded in a vicious bar fight. Unfortunately, I didn’t photograph the coin for a before-and-after photo because I was extremely sceptical that I could effectively and successfully remove the mark from the coin without making matters worse.

I watched countless zany YouTube videos of people boiling gold in pots of Coca-Cola and applying butane burners to gold Pandas in order to remove tarnish and red spots. I wondered if the whole world had gone insane. However, one method in particular caught my attention which involved aluminum foil, hot water, and baking soda (bicarbonate of soda, for you Brits).

I went to the kitchen last night and lined a plastic bowl, shiny side up, with aluminum. I placed my gold Buffalo, obverse side up, in the bowl which I filled with boiling water from the kettle. I nervously added a few tablespoons of baking soda and watched in complete disbelief as the water immediately bubbled and fizzed around the gold coin.

I saw the red spot being lifted from the gold coin, revealing the shiny lustre underneath. After a few minutes, I removed the gold Buffalo with rubber gloves from the hot water which was discoloured yellow and stank of sulfur. I washed the coin under the running tap and dried it on tissue being careful not to rub it clean. I thoroughly inspected the gold Buffalo before returning it to its air-tite capsule. The red spot was gone.

[Shinus73]

I've never tried this with gold, but my experience with silver is that although it removes the tarnish, the coin never looks the same afterwards. It's obvious that it's been treated.

Is this the same with gold, or can you not tell?

[SovTracker]

I've tried it a couple of times on Gold Sovereign's, Proofs and Bullion and it didn't work for me though it might be down to the type of spot or marks they were. The rest of the coin was unaffected.  After trying this method I then washed the coin in hot pre-boiled water, then after cooling, I washed again in deionized water to avoid contaminates then dabbed with a quality lint free microfiber cloth (similar to a lens cloth but best quality). 

Always hold the coin by the outer rim only.

 

[Serendipity]

On 18/09/2019 at 08:42, Shinus73 said:

I've never tried this with gold, but my experience with silver is that although it removes the tarnish, the coin never looks the same afterwards. It's obvious that it's been treated.

Is this the same with gold, or can you not tell?

Yes, you’re right in a way. The tarnish-removal method used in this experiment uses a chemical reaction to convert the silver sulfide back into silver. This does not remove any of the silver like conventional polishing methods. I can’t but help wonder would the tarnish-removal method somehow chemically alter a non-tarnished silver coin in some way to look different from another non-tarnished silver coin which wasn’t dipped in the solution.

[Shinus73]

3 minutes ago, Serendipity said:

Yes, you’re right in a way. The tarnish-removal method used in this experiment uses a chemical reaction to convert the silver sulfide back into silver. This does not remove any of the silver like conventional polishing methods. I can’t but help wonder would the tarnish-removal method somehow chemically alter a non-tarnished silver coin in some way to look different from another non-tarnished silver coin which wasn’t dipped in the solution.

It definitely does.

[Serendipity]

23 hours ago, SovTracker said:

I've tried it a couple of times on Gold Sovereign's, Proofs and Bullion and it didn't work for me though it might be down to the type of spot or marks they were. The rest of the coin was unaffected.  After trying this method I then washed the coin in hot pre-boiled water, then after cooling, I washed again in deionized water to avoid contaminates then dabbed with a quality lint free microfiber cloth (similar to a lens cloth but best quality). 

Always hold the coin by the outer rim only.

 

One of my suspicions as to why it’s not working is that you’re using baking powder rather than bicarbonate of soda. It’s important that you use bicarbonate of soda, not baking powder, or nothing happens. Pure bicarbonate of soda is much more acidic than baking powder and allows the electrochemical reaction to occur.

[Serendipity]

21 minutes ago, Shinus73 said:

It definitely does.

I need to attempt the tarnish-removal experiment on an expendable silver bullion coin when I get the chance to find out what the differences are. It will be interesting to show the results on the Silver Forum.

[kimchi]

On 18/09/2019 at 08:19, Serendipity said:

However, one method in particular caught my attention which involved aluminum foil, hot water, and baking soda (bicarbonate of soda, for you Brits).

Baking soda and Bicarb are slightly different here in the UK.

33 minutes ago, Serendipity said:

One of my suspicions as to why it’s not working is that you’re using baking powder rather than bicarbonate of soda. It’s important that you use bicarbonate of soda, not baking powder, or nothing happens. Pure bicarbonate of soda is much more acidic than baking powder and allows the electrochemical reaction to occur.

Much better advice Bit confused as to your change though!

I would only use distilled/de-ionised water myself, and no straight kitchen products. If you want to achieve results that e.g. allow you to grade then you also need an ultrasonic bath imvho.

 

[Serendipity]

 

1 hour ago, kimchi said:

Baking soda and Bicarb are slightly different here in the UK.

Much better advice Bit confused as to your change though!

I would only use distilled/de-ionised water myself, and no straight kitchen products. If you want to achieve results that e.g. allow you to grade then you also need an ultrasonic bath imvho.

 

I almost made the mistake of using baking powder for the tarnish-removal experiment thinking that’s what Americans mean by baking soda when it’s actually the American expression for bicarbonate of soda. I’m happy, of course, that the experiment removed the red spot from my gold Buffalo with no ill-effects to the coin but still baffled by the science behind the process. We need to err on the side of caution and experiment with an expendable silver bullion coin to find out if the process radically alters the whole chemistry of the coin itself.

[kimchi]

27 minutes ago, Serendipity said:

I almost made the mistake of using baking powder for the tarnish-removal experiment thinking that’s what Americans mean by baking soda when it’s actually the American expression for bicarbonate of soda.

I don't think so - baking soda is used generically (as you say can cover them both) and bicarb is used specifically by those in the know.

[Serendipity]

41 minutes ago, kimchi said:

I don't think so - baking soda is used generically (as you say can cover them both) and bicarb is used specifically by those in the know.

@ChrisSIlver and @HelpingHands can you moderate this post and explain to @kimchi that baking soda is the American term for bicarbonate of soda.

[HelpingHands]

3 minutes ago, Serendipity said:

@ChrisSIlver and @HelpingHands can you moderate this post and explain to @kimchi that baking soda is the American term for bicarbonate of soda.

It looks like you've cleared things up there.

[SovTracker]

6 hours ago, Serendipity said:

One of my suspicions as to why it’s not working is that you’re using baking powder rather than bicarbonate of soda. It’s important that you use bicarbonate of soda, not baking powder, or nothing happens. Pure bicarbonate of soda is much more acidic than baking powder and allows the electrochemical reaction to occur.

Nope - 100% Bicarbonate of Soda. 

I also got a yellowish tinge to the water and a very nice clean coin (apart from the spot which wouldn't shift). 

I've managed to remove dirt, fingerprints and oil marks from Proof Gold Sovereign's. 

[verorl]

I use this method to clean silver jewelry, never have attempted it with a coin... If anyone cleans a silver coin this way, please share the results!

[sovereignsteve]

7 hours ago, Serendipity said:

Pure bicarbonate of soda is much more acidic than baking powder

Totally incorrect I'm afraid.

Bicarbonate of Soda (sodium bicarbonate) is a weak base (alkali) and therefore is not acidic.

Baking powder is a mixture of sodium bicarbonate and tartaric acid, inert in the dry form but when water is added, the acid reacts with the bicarbonate to produce CO2 gas. This helps raise cake mixtures on baking.

[sovereignsteve]

7 hours ago, Serendipity said:

Yes, you’re right in a way. The tarnish-removal method used in this experiment uses a chemical reaction to convert the silver sulfide back into silver. This does not remove any of the silver like conventional polishing methods. I can’t but help wonder would the tarnish-removal method somehow chemically alter a non-tarnished silver coin in some way to look different from another non-tarnished silver coin which wasn’t dipped in the solution.

I've never used the tin foil bicarb method of tarnish removal but I would be interested to see any difference between this method and the traditional silver dip.

You say the bicarb method saves the silver in the silver sulphide back to the coin surface whereas I believe thiourea/acid dips such as EZdip and Goddards simply dissolve away the sulphide. It's easy to see how dipping can adversely affect the surface of the silver but also the depositing of the silver from silver sulphide could also dull the coin surface during the tin foil/bicarbonate reaction.

[Serendipity]

1 hour ago, sovereignsteve said:

I've never used the tin foil bicarb method of tarnish removal but I would be interested to see any difference between this method and the traditional silver dip.

You say the bicarb method saves the silver in the silver sulphide back to the coin surface whereas I believe thiourea/acid dips such as EZdip and Goddards simply dissolve away the sulphide. It's easy to see how dipping can adversely affect the surface of the silver but also the depositing of the silver from silver sulphide could also dull the coin surface during the tin foil/bicarbonate reaction.

The science behind the tarnish-removal method is very complex PhD stuff and there are experts in the field who can explain the electrochemical process far better than I can. I’m not the expert in the field. Here are some links by the experts in the field:

http://www.darylscience.com/Demos/Silver.html

 

[Serendipity]

3 hours ago, SovTracker said:

Nope - 100% Bicarbonate of Soda. 

I also got a yellowish tinge to the water and a very nice clean coin (apart from the spot which wouldn't shift). 

I've managed to remove dirt, fingerprints and oil marks from Proof Gold Sovereign's. 

That’s interesting. The gold coins I’ve seen the tarnish-removal method used on in YouTube videos are 24-karat gold coins like my gold Buffalo. Sovereigns are 22-karat gold with a copper alloy. I don’t know if the copper spots on sovereigns are part of the gold/copper alloy which would be more difficult to remove than the copper surface specs on 24-karat gold coins.

[gazer]

8 hours ago, Serendipity said:

That’s interesting. The gold coins I’ve seen the tarnish-removal method used on in YouTube videos are 24-karat gold coins like my gold Buffalo. Sovereigns are 22-karat gold with a copper alloy. I don’t know if the copper spots on sovereigns are part of the gold/copper alloy which would be more difficult to remove than the copper surface specs on 24-karat gold coins.

Would this method mean its classed as when grading or selling, especially gold Proof and silver collectable?

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Added 0 minutes later...

Just now, gazer said:

Would this method mean its classed (cleaned) as when grading or selling, especially gold Proof and silver collectable?

 

[Serendipity]

1 hour ago, gazer said:

Would this method mean its classed as when grading or selling, especially gold Proof and silver collectable?

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Added 0 minutes later...

 

The general advice professional numismatists give is that coins should never be cleaned. A coin which is suspected to have been cleaned will be graded as such and lose half its value. I’ll showcase my electrochemically treated gold Buffalo on the Silver Forum someday. I’ll let the forum members decide whether it looks treated or not. Unfortunately, I don’t have any before-and-after photos.

[kimchi]

17 hours ago, Serendipity said:

@ChrisSIlver and @HelpingHands can you moderate this post and explain to @kimchi that baking soda is the American term for bicarbonate of soda.

@HelpingHands could you please explain to this confused young whippersnapper that whilst baking soda is more common as a generic term in the US, many Americans use the correct term bicarbonate of soda correctly where appropriate. I can give links to many Youtube videos where Americans do just that should this most serious of disputes ever go as far as arbitration/court.

[HelpingHands]

This is outside my ability.  Ill leave this thread to our new moderator @deliasmith

[Serendipity]

27 minutes ago, HelpingHands said:

This is outside my ability.  Ill leave this thread to our new moderator @deliasmith

Perhaps I should change the topic from copper spots on coins to “The Great British Bake Off” 😆