Accidental trick find for cleaning crusty copper coins!

[K1DDO1979]

I tried many methods for cleaning my dug copper coins that were very crusty and the best method I found was accidental. I have been using it ever since. I dug two large cent and a few 1960's penny's and when I got home I put them on the dash of my car and forgot them till the next day. The windows were up and it was a sunny day so the car got warm/hot. I was surprised the next day to see all the coins have a cracked appearance all over them and when I picked them up all the crust fell off and turned to dust leaving a flawless coin (if it was in good shape to begin with). So ever since if I find a crusty copper coin I lightly wash the loose dirt off and then set it in the car with the windows up and not long after they are ready to brush the crust off. It comes off real easy and if really thick leave it a little longer. It even worked for some of the thickest/hardest crust that I gave up trying to clean. I even put some relics and it worked too. Hope this helps someone out there!

 

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[HenryWaltonJonesJr]

Ingenious, the metal expands from the heat, but the chunks don't. I wonder if this would work in an oven at say 200.

I might freak my wife out though if she thinks I'm cooking! Hmm, anyone know if this would make toxic fumes?

 

[K1DDO1979]

Ingenious, the metal expands from the heat, but the chunks don't. I wonder if this would work in an oven at say 200. I might freak my wife out though if she thinks I'm cooking! Hmm, anyone know if this would make toxic fumes?

I would imagine the oven would work but would have to experiment with temp. I just know the max heat in a car and humidity level seem to be near perfect conditions. It even worked in cloudy weather but slower. Not sure about winter temps though because I haven't known about the trick then. But a car can still get pretty hot with the sun out on some wintering days. I'm sure someone can experiment and find the perfect conditions. Oven to high may make the process to quick and not work as well but who knows!

 

[HenryWaltonJonesJr]

It looks like cars can get up to 130-140 degrees. The amount of cool time might make a difference, but I'd try 250 for 30 minutes on some junk to try it out. The melting point for copper is over 1900 degrees so no fear of that! ; )

 

[HenryWaltonJonesJr]

Have people ever tried to boil coins?

 

[K1DDO1979]

Have people ever tried to boil coins?

A long time ago I did try the boil and it didn't seem to work from what I remember. The crust must stay wet from the water so it won't come off. Dry and heat I think is the key.

 

[ResurrectedVirginia]

I had something similar happen with a breast plate. It dried out rapidly in front of a heater. I noticed all the dirt cracking and contorting and I went to work with a dental pick. Out popped a flawless breast plate. It still has a fair amount of crust on the edges but the portrait is spotless and I never even touched the brass with the pick, water, or brush.

Actually, my avatar is the plate I am talking about, only it is a negative.

 

[K1DDO1979]

I had something similar happen with a breast plate. It dried out rapidly in front of a heater. I noticed all the dirt cracking and contorting and I went to work with a dental pick. Out popped a flawless breast plate. It still has a fair amount of crust on the edges but the portrait is spotless and I never even touched the brass with the pick, water, or brush. Actually, my avatar is the plate I am talking about, only it is a negative.

Nice one. I did a dumb move and oil soaked a thick crusty copper and then later tried scraping the crust off the coin recently that ended up being a key date. I know for a fact if I would have did the heat trick it would have came out with flawless detail. I did serious damage.

 

[Higgy]

I would certainly try the oven method, and set it at its lowest. Bake for one hour, and then try different cooldown methods. I've been a student of metallurgy for a long time (knifemaking), so from what I've learned, the cooling is as important as the heating. Cooling also affects the properties of metals, but at these low temperatures, it will not make any difference to the coin itself, so I think we can remove that variable from worry.

I would try heating then cooling in the freezer, perhaps dry ice if you have some, and maybe try some Chemtronics ES1052 | Freeze Sprays

I'm thinking that the latter would work very well.

 

[HenryWaltonJonesJr]

Interesting idea with the freeze spray follow up. I think you can get the same result just holding a regular canned air upside down.

Would be interested to see any results! The wife won't let me bake coins in the oven and since she's the cook I'm not going to argue and burn that bridge!

 

[HenryWaltonJonesJr]

I do remember from metal working class if you heat copper red hot and then very quickly put it water it gets this neat hot pink patina.

I think they key here that the OP found was slow to warm, lots of warm time and slow to cool.

If someone nails down the temps and time I'd build a coin oven device and sell it to archeologists, colleges and hobbyists.

 

[K1DDO1979]

The thing with the car is there was no cool time when the crust would fall easily off. It just was hot and shortly later the crust would crack all over and would basically fall off with a wipe of the finger. I'm not saying there is a better process out there but I think the main key is time & how dry and hot the air is!

 

[RJ55]

Thanks for this info.

 

[Davers]

Nice one. I did a dumb move and oil soaked a thick crusty copper and then later tried scraping the crust off the coin recently that ended up being a key date. I know for a fact if I would have did the heat trick it would have came out with flawless detail. I did serious damage.

Just wondering ..
What kind of oil did you use?

 

[Davers]

Interesting thread .
Always will to try new methods .

 

[Iron Patch]

Sounds like the same idea as knowing what you find detecting, but not what you miss. How do you know a peroxide soak would not do as well or better? I would certainly need some proof this would remove tough crud because sitting here typing this right now, I'd bet my detector it would not. That said, I would use any method that gave good results!

 

[K1DDO1979]

Sounds like the same idea as knowing what you find detecting, but not what you miss. How do you know a peroxide soak would not do as well or better? I would certainly need some proof this would remove tough crud because sitting here typing this right now, I'd bet my detector it would not. That said, I would use any method that gave good results!

You calling me a liar? Your looking to start another "iron war"! Haha just playing with you!
It for sure worked for me on coins and some relics too but may not under all circumstances. I imagine the coin would have to be in decent shape underneath the crust to begin with and maybe it only works for certain types of build up on the coin. I will try some process pictures next time I get a chance to try it! Defiantly wouldn't hurt a coin to try it!

 

[Iron Patch]

You calling me a liar? Your looking to start another "iron war"! Haha just playing with you!
It for sure worked for me on coins and some relics too but may not under all circumstances. I imagine the coin would have to be in decent shape underneath the crust to begin with and maybe it only works for certain types of build up on the coin. I will try some process pictures next time I get a chance to try it! Defiantly wouldn't hurt a coin to try it!

That's what I suspect, it was decent and the peroxide would have done the same idea. But for the items that are best cleaned dry, it wouldn't hurt to do that first step to move things along.

 

[gunntekk1]

a dehydrator might work

 

[K1DDO1979]

I never tried peroxide yet but I will for sure sometime. Heard its great but does it change the color of the coins?