It is a personal choice and there is no firm rule as to how it will affect the value. Some collectors prefer coins with natural as found patina and some do not. There is wear to some high points of the patina, as well as a trace of encrustation over the patina on the reverse. ![]() This Larssa drachm has the original hoard patina, probably left intact as it is reasonably attractive with an even color over the entire coin. It is my personal feeling coins like this should not be cleaned and can be more desirable like this. Silver coins with attractive natural hoard patina are unusual but this Persian siglos has silver chloride (horn silver) on the reverse which does not detract. Processes used to clean silver coins usually turns them very bright but if done properly the surfaces are not harmed and will re-tone over time resulting in old collection toning. Only rarely is original hoard patina on silver coins attractive, so cleaning is usually necessary. Many groups of silver coins are found with rather ugly patina from a variety of silver reactions including silver sulfide and silver chloride (also known as horn silver) formation. I have never owned a gold coin with Boscoreale patina so in this one instance I have used an image that is not my own on this site. It can occur on coins from other sources and I have seen it on coins dating after AD 79. ![]() One way a true Boscoreale patina results is from exposure heat and possibly sulfur and is named for the Boscoreale hoard recovered from Pompeii after burial by the eruption on AD 79. Image courtesy of Classical Numismatic Group On rare occasions gold coins with a reddish brown discoloration known as Boscoreale patina. Usually any encrustations on gold coins are easily removed without damage to the coin, but there is on type of pinkish encrustation which I see more on medieval Islamic gold than ancient gold, which can be very difficult to remove and usually should be left alone. Many come from the ground looking as new. Unless buried in a corrosive or abrasive environment gold coins change very little with burial and rarely require significant cleaning other than washing off some dirt. This is a complex subject which I can only touch on here. There are also false patinas chemically induced or even painted on coins to hide over cleaning. ![]() Sometimes the two work together to form patina. While referring mostly to chemical changes to the surface, it can include some types of deposits on the surface. Patina is the natural surface changes which occur on ancient coins over centuries of burial or decades in modern collections.
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