Some questions about patina

[MrZun]

I collect Coins from antiquity as most here, mostly Roman Empire and persian empires, i have a quite Variety of Coins with different looks, a Trajan denarius that was cleaned long time Ago and has that dark toning around, some silver that are not Black, but they have that slight yellow toning. My question is, everytime i read about patina and toning, when ancient Coins like these are found, they are found with a Lot of dirt that makes them look even like a bunch of rocks, but when you clean them you are making a restoration of the coin, but some say that some people clean It to bare metal and that its posible to clean and maintain the original patina or toning. My question is, what and How exactly a original toning or patina looks like? Since most silver Coins i see look like they have been cleaned in the past and developed cabinet toning. 

Do original toning is when a silver Coin is when the entire Surface of the coin is Black? Because i have seen people clean Coins recently dug out from the ground and they have some parts with shiny silver colour with a bunch of dirt and horn silver.

Also, is horn silver considered dirt or original toning and should It be removed or not?

[Dafydd]

This is a massive subject @MrZun and there is no perfect answer. In simple terms toning is oxidisation and influenced by mettalurgy, and the purity of the silver, the environment in which the coin was found and its journey afterwards. Put a cleaned coin in a manilla envelope for a year and it will exhibit toning. There is no simple answer to your question. To summarise, silver coins tone differently due to varying environmental factors such as humidity, air pollutants and exposure to chemicals. The alloy composition and storage conditions also affect the toning , leading to unique colouration on each coin. I have black, grey, silver and blue coins. The black ones were probably stored near in an atmosphere containing high levels of sulphur, possibly close to industrial sites.

 

[John Conduitt]

Toning is what happens to silver when it is in contact with air (usually oxidation). This is the coin physically reacting with the air. The end result of full toning is a black coin, at which point it stops because the coin is protected by the oxidised layer. This can take a very short or very long time depending how it is stored. It can even happen at different speeds on the same coin, which is how you get patchy toning.

Patina is what happens to copper when it is in contact with the air (usually oxidation). This is the coin physically reacting with the air. The end result is light green, but before that it is red-brown, dark brown and dark green. Depending on the environment, it may stop at any of these stages.

Dirt (soil) and encrustations (other chemicals that fix to the coin more firmly) are not toning or patina (the coin does not usually physically react with them) and come from whatever is around the coin when it is buried. Because they did not react with the coin these can be cleaned off, but in that process the toning or patina might also come off, since it is a very thin layer (atoms thick). What the dirt and encrustations are determines how much cleaning is needed and so how much toning/patina comes off. This happens to most ancient coins and is not a problem if cleaned properly (not too harshly), since only a thin layer has been removed and it will retone/repatinate. Some encrustations may react with the coin metal, in which case you cannot clean them off since the surface of the coin is now part of the encrustation.

Edited May 25 by John Conduitt

[MrZun]

1 hour ago, John Conduitt said:

Toning is what happens to silver when it is in contact with air (usually oxidation). This is the coin physically reacting with the air. The end result of full toning is a black coin, at which point it stops because the coin is protected by the oxidised layer. This can take a very short or very long time depending how it is stored. It can even happen at different speeds on the same coin, which is how you get patchy toning.

Patina is what happens to copper when it is in contact with the air (usually oxidation). This is the coin physically reacting with the air. The end result is light green, but before that it is red-brown, dark brown and dark green. Depending on the environment, it may stop at any of these stages.

Dirt (soil) and encrustations (other chemicals that fix to the coin more firmly) are not toning or patina (the coin does not usually physically react with them) and come from whatever is around the coin when it is buried. Because they did not react with the coin these can be cleaned off, but in that process the toning or patina might also come off, since it is a very thin layer (atoms thick). What the dirt and encrustations are determines how much cleaning is needed and so how much toning/patina comes off. This happens to most ancient coins and is not a problem if cleaned properly (not too harshly), since only a thin layer has been removed and it will retone/repatinate. Some encrustations may react with the coin metal, in which case you cannot clean them off since the surface of the coin is now part of the encrustation.

So, there is nothing wrong with ancients being cleaned since almost all of them need to be cleaned/restored? And its to be expected for the original toning to come off most of the times?

[MrZun]

I gonna post the Coins i have so Far, do you think they were properly cleaned? Also, How do i spot a overcleaned Coin?

[MrZun]

[John Conduitt]

38 minutes ago, MrZun said:

So, there is nothing wrong with ancients being cleaned since almost all of them need to be cleaned/restored? And its to be expected for the original toning to come off most of the times?

Yes. The only reason modern coin collectors don't like cleaning is because it removes mint lustre, but with ancients, few coins come straight from the mint (so are circulated) and the environment took off the rest.

Edited May 25 by John Conduitt

[John Conduitt]

27 minutes ago, MrZun said:

They look fine.

You can't actually tell most 'over-cleaned' coins because it depends what state they were in to start with. Some people say bright white coins are over-cleaned but that isn't necessarily true. Maybe it needed harsher chemicals and heavier mechanical cleaning. But it usually means when someone takes a wire brush to it and scratches it up.

[Octavius]

I also think your coins look fine. You have some quite handsome ones there. They do not look harshly cleaned. If they were never cleaned at all after coming out of the ground, I don't think anyone would buy them.

[AussieCollector]

On 5/26/2024 at 7:16 AM, MrZun said:

So, there is nothing wrong with ancients being cleaned since almost all of them need to be cleaned/restored? And its to be expected for the original toning to come off most of the times?

Yes. This sums it up.

[Ten-Speed]

I hope this is on topic. I particularly like coins with green patina but sometimes it seems difficult to tell the difference between coins with patina/malachite and bronze disease. It seems if there is green material that comes right off it is probably bronze disease.

Edited Wednesday at 12:50 AM by Ten-Speed
accuracy