Just a question and I'm not expecting to get an answer. Gold and silver DON'T corrode, but copper-coins do. If a copper coin from year 1000 was thrown in earth and another one on the bottom of the sea, and you pick up both of them in year 2000, would you be capable of telling which one was on earth and which one was on sea based on the condition of the coins? How do copper-coins look like if they were in sea-water for hundreds of years? Do they corrode in a different way? Can you provide images to illustrate the difference? Do you have copper-coins that you KNOW was buried in seawater? As mentioned I'm not expecting to get an answer. Thanks.
I would think that very acidic soil would corrode copper almost like sea water. I think that different composition soils determine that. Metal detecting finds vary greatly depending where they're found.
Here you go, a copper coin (Swedish plate money) which was in seawater for 200 years or so. Most of the surviving examples were from a single shipwreck, as many of the others were melted down when the price of copper rose. As you can see, the seawater did quite a bit of damage in just 200 years. Compare to Roman coppers which have been buried for ~2000 years, and still look pretty good. In general, I would guess seawater is a much harsher environment. Also, though silver does not corrode quickly from oxygen, it does corrode from sulfur, which will eventually permanently damage it. So depending on the chemistry of the soil in which a coin was buried, one might get very different results. Any many buried coins were somewhat protected by being in a container.
Thanks for that image. Can u post an image of a perfect plate of that Swedish plate money? I just want to see how it looks like.
Copper wouldn't last in either for 1000 years . The corrosion would be so bad the coin would most likely be a slag piece of metal . I don't have a Copper coin to show you that's 1000+ years ,but I do have one almost 300 years old ( barely read it- 1733 King George Copper. This was found on land in 2012 by me . Look at the damage., its extramental . I think that's he word. LOL
Here's a search on Numista for "Sweden Plate Daler" which gives several examples of non-salvage dalers. There's a few 4 dalers like mine for comparison, as well as other sizes.
The answer depends upon a number of factors such as depth of soil, acidity level, moisture levels (frequency of water contact and duration), etc. for earth buried coins. Coins in salt water constantly shifted by wave or current action versus static position and accumulating sediment with both affected by water temperature are some considerations to consider. The coin affected the most would be the one shifted by water movement which would cause accelerated wear. Now to your question. Given immobility, the salt water coin would suffer the most, IMO.
I don’t have a copper coin from sea, but I do have an Early Chola era (~100-200 AD) copper coin picked out from a river bed (not by me), as the local vendors would buy these coins from local people who scavenge these coins along the beds for few cents worth of money, which the sellers would then sell them in auctions and online shops! You can see how the coin has a stratified form of corrosion just like the stratified rocks due to constant water and sand abrasions.
There are some on this page. I used to own a 4-daler piece from the Nicobar shipwreck off South Africa. I think it was dated 1750, if I remember correctly. Very cool things.
I have many coins from ship wrecks/ where unearthed. As far as I can see, they suffered no adverse effects. The AV 8Escudos 1751-So Santiago Mint/ Chile/ Fernando VI salvaged from Luz wreck The Catuvellauni/ Trinovantes AV Quarter Stater was found by a metal detectorist in UK.
For the record, silver does also corrode in saltwater, and not just the copper that might be in the mix. My other passion in coin collecting is "age of sail" coins, and I can tell you silver coins commonly lose up to 40% of their weight, even after only a couple hundred years submerged.
After 1600 years on the ocean floor Source https://www.google.com/amp/s/www.nu...ld-coins/shipwreck-yields-ancient-coin-bounty
^^ I am all of a sudden feeling not so guilty about the occasions where I got a tiny bit of finger moisture on my coins.
Silver actually corrodes quite easily, not as quickly as bronze, but fast enough. If you want to see the effects of seawater corrosion on bronze or copper, a good example can be seen with this example of Swedish copper plate money, salvaged from the Nicobar wreck, 1783 in 1987. As can be seen, there is major corrosion resulting in a good portion of the plate eaten away. Still, there is a demand for plate money on the part of some collectors. This example is priced at $2,600. As with many situations involving sea salvaged coins, the condition of the coin depends on factors that either increase exposure to salt water, or reduce exposure, such as being in the middle of a pile of coins or quickly buried in muck that has little oxygen.
"For the record, silver does also corrode in saltwater, and not just the copper that might be in the mix." "Silver actually corrodes quite easily, not as quickly as bronze, but fast enough." You are right. I have seen corroded silver coins of Byzantium before, but I thought that they were just not pure silver: https://assets.catawiki.nl/assets/2019/3/28/f/1/4/f148d7a0-1593-4b22-a1b8-edccd5e530b4.jpg Silver actually does corrode unlike what I stated earlier.
