Difference Between Patina Or Dirt

Patina (also known as toning), whether it's colorful or gray, is integral to a coin's surface.
Remove it and you've cleaned the coin; you've changed the surface.

Dirt (along with glue, tape, etc.) is just foreign debris on a coin's surface.
Removing it is called conserving and is generally done with such things as distilled water or acetone.
Once removed you can see the current state of the surface of a coin.
That could be pristine or damaged but NOT changed.

This coin has a black patina, the bronze of the coin has toned to near black. The coin was found in an environment where a build up of dirt/sand has attached to the coin. This sand has been left on the coin as it is sometimes deemed attractive. This can be referred to as desert patina but is dirt on top of a patinated coin. The dirt may be hiding damage, it may not.



Here the patination is green and in cleaning the coin they have either exposed a damaged surface or damaged the surface by over cleaning through the patina



Bronze coins typically patinate to shades of brown. The following coin was originally silvered and the toned bronze can be seen a partially silvered surface, which has itself toned to a golden colour.



Bronze can go to a variety of shades of green too.



The high points on this coin have been cleaned back to the bare metal through the patina. These parts have been over cleaned.

Olive oil does well to remove debris, but it can take years. If you have the patience you can still have the original patination undisturbed.

When cleaning a coin, you keep going until there is only patina left or when the remaining dirt/encrustation is visually pleasing. Olive oil will darken the patina but distilled water will not. Distilled water can be very slow - I would say it isn't a matter of days, it isn't a matter of weeks, it is a matter of months. A lot of patience is needed - it can be very tempting to break out picks and scalpels against better judgement.

That is correct many people mistake toning and patina. Here is my example - a horrible over cleaning. There is noway I would leave it like that so I used liver of silver and got a decent result. Of course, I'd rather the patina, but cleaning is a process of learning

The following coin illustrates a challenge on ancients. This is how the coin has reacted to everything around it over the years. We end up with green "adhesions". This is more than dirt as it is a chemical reaction between the coin as the environment. The coin as it stands is really ugly. Under the green layer there may well be a partially silvered coin but the green is bonded to the surface. It can be mechanically cleaned but it is not something that I would undertake. I live with the coin as it is.



The following shows a partly cleaned coin where the black adhesions have been partly removed. The coin might well be far more attractive it were all to be removed but I keep it this way.



People should be aware that there are ancients that are sold with a "desert patina" where the sand/dirt has been newly added to try and make an unattractive coin have more eye appeal. Glue is applied to the surface, filling pits in the surface etc. and then the coin is dusted with fine sand and brushed. I find this process reprehensible. Be careful out there.