Sliver coins and what that eggy smell is

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41 Craig P
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Sliver coins and what that eggy smell is

Post by 41 Craig P » Fri Mar 18, 2016 9:40 am

I am still new here but I have noticed lots of people mention the eggy smell on silver coins when you rub them but I thought I would expand a little on what goes on chemistry wise with the eggy smell. I hope I am not teaching anyone to suck eggs with this but I thought it may answer questions those people have when they wonder what the eggy smell is.

The Tarnish on Silver is caused by a reaction of Hydrogen Sulphide with the silver to form Silver Sulphide and hydrogen as a by product. Its not necessarily a reaction but Sulpher has a greater affinity with Silver than Hydrogen.

So on the silver coin the black areas you see are Silver Sulphide. Rubbing or using metal polish removes this silver sulphate so taking with it a small amount of silver too. The foil method is the safest way as it does not remove the silver but converts the sulphide back to silver. This is because like the move from hydrogen to silver. Sulpher has an even greater affinity to Aluminium.

When you "spit" and press the coin between the foil you are in fact doing a small scale Electrolysis. Your spit acts as the electrolyte to assist in the reaction. From this a reaction between the Silver Sulphide and the Aluminium occurs the transfer gives off some Sulpher Gas and this is the eggy smell you experience. This in turn leaves the silver in place on the coin.

I have made some diagrams to explain. The website below explains it a lot better than me.
http://www.compoundchem.com/2013/12/16/ ... sh-silver/

Again apologies if this is obvious to some I just never seen it explained in any of the posts and thought it might be of interest to some.
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Re: Sliver coins and what that eggy smell is

Post by lardbelly » Fri Mar 18, 2016 9:46 am

Cheers Craig ::g That explains it rather well.

A couple of points, if I may while we're on this subject.

1. This may sound daft but I've always used the 'non shiny side' of silver foil when doing this. Is this correct as I don't think I've ever seen it stated?
2. I've also used lemon juice when doing this and have found it works as good, if not better, than spit. Anyone else noticed this?
3. When using just lemon juice (in a bowl to soak the coin) how long do people leave it?
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Re: Sliver coins and what that eggy smell is

Post by f8met » Fri Mar 18, 2016 10:49 am

I found this article a few months back and it seems a weak acid solution was one of the best methods. As always don't do it on rare or valuable coins.

http://www.jcms-journal.com/articles/10 ... s.1021204/" onclick="window.open(this.href);return false;
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Re: Sliver coins and what that eggy smell is

Post by Resurgam » Fri Mar 18, 2016 11:03 am

I recently found a silver ring in damp (not wet) sand and it came out looking like new. At fourteen inches deep, I had assumed that it had been there for a good while but it did give off some eggy smell when treated with a bit of spit and some foil.

The back half of a silver cigarette case was a different matter. Upon treating the said item the same way, the darned thing stunk the caravan out and I had to open all the windows. Although not exacting, I suppose the amount of tarnishing can be a good indication as to how recent the loss of an item was.

Many thanks for a most interesting and explanatory post. ::g
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Re: Sliver coins and what that eggy smell is

Post by oldartefact » Fri Mar 18, 2016 11:22 am

41 Craig P wrote:I am still new here but I have noticed lots of people mention the eggy smell on silver coins when you rub them but I thought I would expand a little on what goes on chemistry wise with the eggy smell. I hope I am not teaching anyone to suck eggs with this but I thought it may answer questions those people have when they wonder what the eggy smell is.

The Tarnish on Silver is caused by a reaction of Hydrogen Sulphide with the silver to form Silver Sulphide and hydrogen as a by product. Its not necessarily a reaction but Sulpher has a greater affinity with Silver than Hydrogen.

So on the silver coin the black areas you see are Silver Sulphide. Rubbing or using metal polish removes this silver sulphate so taking with it a small amount of silver too. The foil method is the safest way as it does not remove the silver but converts the sulphide back to silver. This is because like the move from hydrogen to silver. Sulpher has an even greater affinity to Aluminium.

When you "spit" and press the coin between the foil you are in fact doing a small scale Electrolysis. Your spit acts as the electrolyte to assist in the reaction. From this a reaction between the Silver Sulphide and the Aluminium occurs the transfer gives off some Sulpher Gas and this is the eggy smell you experience. This in turn leaves the silver in place on the coin.

I have made some diagrams to explain. The website below explains it a lot better than me.
http://www.compoundchem.com/2013/12/16/ ... sh-silver/

Again apologies if this is obvious to some I just never seen it explained in any of the posts and thought it might be of interest to some.
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Excellent post Craig ... but I have two questions ... where does the hydrogen go, and can the electrolyte be water?
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Re: Sliver coins and what that eggy smell is

Post by oldartefact » Fri Mar 18, 2016 11:25 am

lardbelly wrote:Cheers Craig ::g That explains it rather well.

A couple of points, if I may while we're on this subject.

1. This may sound daft but I've always used the 'non shiny side' of silver foil when doing this. Is this correct as I don't think I've ever seen it stated?
2. I've also used lemon juice when doing this and have found it works as good, if not better, than spit. Anyone else noticed this?
3. When using just lemon juice (in a bowl to soak the coin) how long do people leave it?

Just a complete guess on what craig will come back with .. but I would hazard a guess that the lemon juice removes the silver sulphide and in so doing removes some of the silver also... just a guess though.
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Re: Sliver coins and what that eggy smell is

Post by slowsweep » Fri Mar 18, 2016 11:27 am

i like to keep my finds in "as found" condition, i personally dont like to remove any of the items history, most of my coins still have earth in the detail, shiny silver coins are "UGLY" imo, some like them like that and thats fine but its not for me.
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Re: Sliver coins and what that eggy smell is

Post by f8met » Fri Mar 18, 2016 12:04 pm

And if the finds turn out to be part of a hoard / treasure item it could effect the value.
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Re: Sliver coins and what that eggy smell is

Post by 41 Craig P » Fri Mar 18, 2016 12:13 pm

oldartefact wrote: Excellent post Craig ... but I have two questions ... where does the hydrogen go, and can the electrolyte be water?
Salt water is the best electrolyte. The hydrogen reacts with oxygen to go back into water in the soil I believe and if it is exposed to air it will just become part of the atmosphere.
oldartefact wrote: Just a complete guess on what craig will come back with .. but I would hazard a guess that the lemon juice removes the silver sulphide and in so doing removes some of the silver also... just a guess though.

I would agree lemon is an acid so will be removing the substance rather than reversing the reaction that occurred.

Patina does add value so it is how you go about this that you need to think of. I left my hammered coin in salt water for about 5 mins it let the surface detail shine and only removed a small amount of tarnish on the deeper area so still had a fairly nice patina. If I had left it in for 10 mins it would have been full on shiney.

You need to use the Shiney side of foil as I believe the non shiney side has a thin layer to it that blocks the electrochemical reaction taking place.
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Re: Sliver coins and what that eggy smell is

Post by oldartefact » Fri Mar 18, 2016 4:13 pm

slowsweep wrote:i like to keep my finds in "as found" condition, i personally dont like to remove any of the items history, most of my coins still have earth in the detail, shiny silver coins are "UGLY" imo, some like them like that and thats fine but its not for me.
Some of my hammereds come out dark grey/black, aand some come out all shiny and new.. I like both sorts.. ::g ::g ::g ::g but why they come out so shiny after 700 years in the ground defeats me.
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Re: Sliver coins and what that eggy smell is

Post by Stillburning » Fri Mar 18, 2016 5:23 pm

Very interesting explanation, thanks for posting ::g
Some of my hammereds come out dark grey/black, aand some come out all shiny and new.. I like both sorts.. ::g ::g ::g ::g but why they come out so shiny after 700 years in the ground defeats me.
I had one that came out almost black on one and shiny on the other, I clean the hammered as little as possible to get the point where an ID can be made, milled silver 19th century onwards I clean a bit more.
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Re: Sliver coins and what that eggy smell is

Post by Grott » Sat Mar 19, 2016 10:06 pm

I love the eggy smell. You take this black coin home and think is it or is not silver, a rub with tin foil and the smell puts a smile on your face.

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Re: Sliver coins and what that eggy smell is

Post by f8met » Sun Mar 20, 2016 12:44 am

I try and blame it on the dog......
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Re: Sliver coins and what that eggy smell is

Post by TreeCamper » Fri Apr 28, 2017 9:32 am

Sun God Pendant.JPG
We are newbies and on our 4th hunt I was finding nothing but trash on a beach. So I thought I would let the GF have a go. Straight away she found some coins.
But our first bit of real treasure came up as a Silver Sun God Pendant. It was surprisingly shiny and had 925 on the back so I assume its Sterling Silver. The beach sand was damp so I suppose the saltwater kept it somewhat clean. I have seen wreck finders finding silver coins underwater and they set solid in a black crud. I will give the Tinfoil, hot water and bicarb a go and see if it gets rid of the little black bits. Here is the result just boiled for about 5 mins. Very gentle rub with a toothbrush. Seems to work just fine.
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Re: Sliver coins and what that eggy smell is

Post by oldartefact » Fri Apr 28, 2017 6:26 pm

Both are very nice indeed ... but I like the one with the little black bits best.
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Re: Sliver coins and what that eggy smell is

Post by Phil2401 » Fri Apr 28, 2017 7:34 pm

Anybody else remember those little glass vials you used to be able to buy from the joke shop (or maybe still can)? Stink bombs - I believe that was hydrogen sulphide gas too - how did that work then?
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Re: Sliver coins and what that eggy smell is

Post by jeff82 » Fri Apr 28, 2017 7:41 pm

Thank you for the informative post .. I have been wondering about this as I have seen it mentioned
I have a suspected silver ring and a pendant I am going to try this on
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Re: Sliver coins and what that eggy smell is

Post by jeff82 » Fri Apr 28, 2017 7:43 pm

Tree camper .. that's a beautiful find .. very nice job on the clean up but for me I like the original state ::g
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Re: Sliver coins and what that eggy smell is

Post by ossie » Fri Apr 28, 2017 9:16 pm

I just been out in the garage where my caravan battery was on charge and there was a very strong smell of rotten eggs,plus my battery was swollen up fit to burst,so recon i was lucky to catch it before the bang. Is this the same process as the foil trick?

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Re: Sliver coins and what that eggy smell is

Post by Hauptmann aD » Sat Apr 29, 2017 10:21 am

The problem here in Germany are not the good silver coins, but those coins, which are made from billon, an alloy from silver and copper with more copper in it than silver.
This is such a sample coin, agreed, the ground was not friendly:
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