Cleaning coins with baking soda?

[MBA101]

I have heard about people doing this and always wondered why people would attempt cleaning a coin with an abrasive. But actually, that is NOT what you do. The correct method of cleaning a coin using baking soda is to place a coin in a vessel on top of a sheet of aluminium foil, boil some water and add the baking soda, then add the baking soda solution to the vessel. Here is a junk silver 1922 peace dollar (that my dad got when he was a kid from the bank) with some not so great toning:

 

 

Here it is, nearly blast white with decent boom to its luster (there is some haze that did not change, and the dark toning on the reverse is not as dark as it appears in the photo)

 

 

The luster actually booms rather nicely. A bit of the deeper tarnish remains, but its not bad. What actually happens is the battery effect. The baking soda reacts with the silver sulfide, turning the silver sulfide back into silver in a reaction with the aluminium. The equation:

 

3 Ag2S + 2 Al --/> 6 Ag + Al2S3

silver

sulfide aluminum silver aluminum sulfide

 

Fun with Chemistry!

 

Thoughts?

 

 

[bsshog40]

I think it's just a little faster to dip in ez-zest for about 2 seconds.

[e1cnr]

galvanic cleaning has been used on crusty old stuff

too many people just make a paste and tooth brush - not good

 

galvanic cleaning explained

 

 

 

How is the luster on your Peace dollar? Do you feel it is better, the same, or worse? Many people don't like dipping because if it is done enough times, the luster is gone and it becomes dull, lifeless and cleaned

[MBA101]

galvanic cleaning has been used on crusty old stuff

too many people just make a paste and tooth brush - not good

 

galvanic cleaning explained

 

 

 

How is the luster on your Peace dollar? Do you feel it is better, the same, or worse? Many people don't like dipping because if it is done enough times, the luster is gone and it becomes dull, lifeless and cleaned

 

From what I read, you are not removing metal, just removing the sulfur compound and transferring it to the Aluminium. The luster is great and the surfaces are not harmed, though the areas where the toning is deeper have ghost toning. The luster is quite nice now.

 

I did a severely tarnished dime first and it looked better with said tarnish.

[MBA101]

I think it's just a little faster to dip in ez-zest for about 2 seconds.

 

The usual dips remove metal, which is why i am curious about a galvanic method for removing toning, which actually reverses the toning, without removing metal.

[RWB]

Converting silver sulfide or chloride back to metallic silver does not "reverse" the toning. It will remove the color of the sulfide but spacing of the silver atoms and the broken crystal lattice remain. That, I suspect, is what the OP is calling "ghost toning."

[Walkerfan]

I wouldn't have messed with it. I still don't like the idea of using baking soda. IMHO.

[MBA101]

Converting silver sulfide or chloride back to metallic silver does not "reverse" the toning. It will remove the color of the sulfide but spacing of the silver atoms and the broken crystal lattice remain. That, I suspect, is what the OP is calling "ghost toning."

 

No, the galvanic reaction pulls out the Sulfur atom and reacts it with the Aluminium. The ghost toning is just deeper toning (it was darker toning to begin with, and may be removed with a longer soak, but then again, maybe not).

[RWB]

By "pulling out the Sulfur atom" the silver atom is left in a different place in the lattice than it was in the original alloy. the silver does not return to it's "original" location or crystal structure.

[MBA101]

By "pulling out the Sulfur atom" the silver atom is left in a different place in the lattice than it was in the original alloy. the silver does not return to it's "original" location or crystal structure.

 

The Sulfur atom was not there in the first place. What you are suggesting is that the Sulfur atom moved the Silver over and out of its way, but the Silver atom does not move back whence it cam. I am saying the Silver atom never moved in the first place, just had a Sulfur atom move in next to it and bonding to create the tarnish. The holes are always there that is why the reaction occurs.

 

Now I am only talking about Sulfur, as other tarnishes I do not think are effected by this method.

[messydesk]

That, I suspect, is what the OP is calling "ghost toning."

I would call this "scarring"

[MBA101]

That, I suspect, is what the OP is calling "ghost toning."

I would call this "scarring"

 

No the "ghost toning" is just the deeper layer of toning that has not reacted with the aluminium.

[A.Phillips]

IF you submitting it to grading service after dipped into the baking soda... Will it comes back as improperly cleaned? I hope so.

 

In my opinion, I don't like the idea about dipping it into baking soda.

[MBA101]

IF you submitting it to grading service after dipped into the baking soda... Will it comes back as improperly cleaned? I hope so.

 

In my opinion, I don't like the idea about dipping it into baking soda.

 

Baking soda is not eating the coin. there is a chemical reaction taking place where the Sulfur compound is being transferred from the Silver to the Aluminium.

 

BTW, submitting a 20 dollar coin to a grading service is kinda silly IMHO

[RWB]

The molecular sizes and crystals are different - you cannot remove the sulfur and magically move the silver back to its original configuration. It is a chemical process which also creates a physical change.

 

i.e.: S combines with the Al because Al is more reactive than Ag, leaving elemental Ag.....Ag2S is larger than Ag and leaves space when the S is combined with Al. The original silver crystal lattice is not restored and this creates areas that look different on a macro scale as large areas of Ag2S are altered.

[Conder101]

When toning forms the sulfur doesn't just sit next to the top layer of silver atoms. It disrupts the structure of the metal latticework and exposes the lower layers (This is why the toning continues and eventually eats into the metal.) When the sulfur leaves and combines with the aluminum it leaves that disrupted structure behind. That damaged structure does not reflect or scatter light like the original surface did. Repeated cleaning/toning cycles will eventually result in the same dead lifeless surfaces that can result from overdipping in the acid solutions.

[Kurtdog]

I think it's just a little faster to dip in ez-zest for about 2 seconds.

What a waste. At least with baking soda when you get all done you can brush your teeth with it.

[bsshog40]

I think it's just a little faster to dip in ez-zest for about 2 seconds.

What a waste. At least with baking soda when you get all done you can brush your teeth with it.

[MBA101]

When toning forms the sulfur doesn't just sit next to the top layer of silver atoms. It disrupts the structure of the metal latticework and exposes the lower layers (This is why the toning continues and eventually eats into the metal.) When the sulfur leaves and combines with the aluminum it leaves that disrupted structure behind. That damaged structure does not reflect or scatter light like the original surface did. Repeated cleaning/toning cycles will eventually result in the same dead lifeless surfaces that can result from overdipping in the acid solutions.

 

if that is the case, then what i did is fine for removing some splotchy surface toning. it did leave a bit of deeper toning, but overall I thought it was rather cool to see this in action.

 

Disclaimer: This was only an experiment and I do guarantee you can ruin a coin that has heavy toning.

 

I have never heard of this galvanic method before and thought it to be interesting, and actually quite useful for removing ugly surface toning and bringing the luster back to life.

[physics-fan3.14]

What does the baking soda do? Why is it important? It seems to be a reaction with the silver and aluminum foil? Could you use a different solution?

 

Since this seems to be a reaction solely with silver sulfide, it is entirely possible that the remaining toning is due to another compound.

 

And yes, the crystal lattice will not be returned to its original form. However, this method has obvious benefits over a dip (in that, theoretically, no silver is being removed).

[MBA101]

Here is where i found the experiment

 

http://scifun.chem.wisc.edu/homeexpts/TARNISH.html