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 Replies: 16 / Views: 2,705 |
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Pillar of the Community
 United States
900 Posts |
I have a number of uncirculated mexico pesos from 1922 to 1945. A number of them have a residue that kind of resembles concrete powder (for lack of a better description). Usually it is only on the chest and feathers of the eagle, but in this one example it is prevalent all over. Any idea what this is? It seems I've seen this on some of the coins on ebay as well.   I figure I will try soaking in acetone, but would be interested in knowing what this is. |
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New Member
United States
47 Posts |
Jadey, I wish I had an answer for you, but I'm only posting to sympathize. I collect those pesos too, have noticed the same residue (it's whitish, right?), and have no idea what it is.
Any luck with the acetone?
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Pillar of the Community
United States
1915 Posts |
Looks like tarnish to me, and a good number of my pesos looked similar. I don't suggest it, but washing the coin in your hands with baking soda will remove it.
Some may not agree with me saying "tarnish", but if you study properties of metallic silver and how it reacts, and what different levels of tarnish look like, you may agree.
In your case the tarnish is a dull grey color. It may look frosty or even black. Silver "saves itself" and reacting with the elements on the surface preserves the underlying metal.
I came back to add a bit more: a number of my pesos had this dull grey color "tarnish" and I think it has to do with the Mexican silver itself. Other silver coins of mine developed sort of a "frosty" appearance and some colors were a faint hint of pink on one coin and a faint hint of brown on another. I believe it has to do with the silver, the copper, impurities, ratios of impurities, environment and having contact with things like paper, cardboard, plastics, heat, light, humidity and so on.
Edited by Albert
01/05/2019 1:31 pm
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Pillar of the Community
United States
7955 Posts |
It will be interesting to see if some kind of solvent wash helps remove it or not.
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Pillar of the Community
United States
1915 Posts |
If that is the goal, and it may be wrong by others that say never to clean coins...., but if that is still the intent then place your hands under warm running water as if washing your hands. But dump a good amount of baking soda with the coin in the palm of your hands and rub them together. Maybe using your thumb to rub the warm water soda paste in. Should leave the coin with an unnatural sheen and restore it's shine. But you may not like the look of the shine it produces and you might prefer the original look. I guess if it is for instructional purposes, I don't see the harm if one wants to try to take a chance on improving the looks of the coin. I'd be interested too in finding out the result.
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Pillar of the Community
 United States
900 Posts |
Thank you for the responses. I tried the acetone soak and it made no difference. I have been perusing ebay, and notice the same thing on many of the coins I see there. Baking soda might help, but I suspect it would be particularly damaging because most of the "residue" is in the crevices and would need to be scrubbed to affect a change. I used to use baking soda when I was a teenager, and I can clearly see the effects on those coins. |
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Pillar of the Community
Spain
2752 Posts |
Check out distilled water and lemon juice...?
Seems to work.....But be careful with the amount of juice!
Edited by Palouche
01/06/2019 7:44 pm
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Pillar of the Community
United States
900 Posts |
I have a handful of 50 centavos pieces from the same time period, and noticed that a couple of those have the same issue. It is very odd, because I've never seen this issue on any other silver pieces. I have a lot of mexican silver as well that is admittedly more recent, but does not show any of the same signs.
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Pillar of the Community
United States
900 Posts |
@Albert
I think the terms "gray" and "frosty" accurately describe what I see.
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Pillar of the Community
United States
900 Posts |
Quote:
Check out distilled water and lemon juice...? I have tried lemon juice on some metal detecting finds, and it definitely works. I just wonder if that removes the luster, because the coins still have nice luster in the fields. |
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Pillar of the Community
United States
1005 Posts |
The simple answer is yes, lemon juice will remove some of the luster from the coin. Depending on how long is is soaked or how many times it is soaked, it might not remove all of the luster but every time you do it you are removing some of it.
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Pillar of the Community
Spain
2752 Posts |
 ....You've got the coin in hand its your choice..... I must admit being an ancient coin collector I quite like it how it is !...Paul |
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Pillar of the Community
United States
900 Posts |
I'll just leave them as they are, since I'm selling most of them anyway. I just thought someone might have some insight on this. Tarnish seems like the best answer thus far.
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Pillar of the Community
United States
7955 Posts |
Given that these are low silver content, maybe it is impurities that are oxidizing like happens at the surface of aluminum or zinc coins? You could always take your least favorite and try the diluted lemon juice approach (acid might react with these surface oxides even if it would not react with silver.)
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Pillar of the Community
United States
900 Posts |
I did the acetone bath, then 2 minutes in diluted lemon juice, and then 3 more minutes, taking pictures after each step. The acetone gave no noticeable improvement, but the lemon juice definitely brightened the coin.
After acetone - no improvement (Unfortunately I lost the reverse photo for this step.) 
After 2 minutes diluted lemon juice - noticeable difference  
After additional 3 minutes diluted lemon juice  
I removed the diffuser for these last two pictures, because there is a big before/after difference that is not that apparent in the photos. Unfortunately, I did not do the same at the beginning.   My conclusion is that the coin actually looks better and more lustrous than it did originally. That is not to say that it has full luster. The luster is rather low, but not as low as it was originally. Better or worse? That is a matter of opinion, but I would say it has better eye appeal. |
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Pillar of the Community
Spain
2752 Posts |
Hope you dont mind JD but I took the liberty of posting your coin Before/After. Nice idea of taking progressive photos  It will be interesting to hear peoples opinions...  |
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Replies: 16 / Views: 2,705 |
Posted 01/05/2019 01:11 am
