If Cleaning Is Taboo - Where Does This Fit?

Cleaning is not "taboo". But it's like amputation - something that should only be done as a last resort, by people that (hopefully) know what they're doing rather than trying to do it yourself. Because, like amputation, cleaning a coin is irreversible. You can't clean a coin and then "dis-clean it" because it looked better before you cleaned it.

The advice given to newbies should always be, "never clean coins", because new collectors simply don't know the difference between dirt, corrosion and patina. All too often, newbies want to make their coins "look like new again" - they should be discouraged from attempting any sort of cleaning until they learn that this is an impossible goal. Cleaning is a tool of last resort, and only coins that "really need it" should be cleaned.

"Dirt", as in foreign matter adhered to the surface of a coin (eg. paint, goo from degraded plastic or literal dirt from being buried in the ground) can be removed safely and with minimal concern for the ethics of what you're doing. Soap and water, acetone or some other solvent removes dirt but doesn't damage corrosion or patina.

"Corrosion" is more commonly encountered on copper and bronze coins, though any metal apart from pure gold can suffer from it. Either treated or untreated, a corroded coin is an ugly, damaged coin. Treating it might make the coin look better, but then again might make the coin look like a closeup of the Moon. The other thing to consider is that some forms of corrosion "spread" and if left untreated in humid conditions will eventually see the whole surface of the coin crumble into dust. Fire damage also qualifies as corrosion; again, an ugly coin might be improved by removing the corrosion, but it might be made worse.

"Patina" is the thin oxide surface of the metal itself. In effect, it's a very thin layer of corrosion, but is both attractive and serves as a protection against worse forms of corrosion. Removing it is considered "cleaning" in the most negative sense of the word, and should be avoided if at all possible. A coin stripped of its patina definitely "looks cleaned" and using chemicals or adverse environmental conditions to artificially re-patinate a coin to make it look "not cleaned" again is deceptive and unethical - two wrongs don't make a right.

Coins dug up from the ground pose a particular challenge. Ancient Greek and Roman bronze coins typically come out of the ground looking like rocks, with a remnant core of uncorroded metal surrounded by a thick uneven patina surrounded in turn by corrosion byproducts and concreted soil; finding exactly where the boundaries are between dirt, corrosion, patina and bare metal for these "uncleaned ancient coins" is a skill few have the patience to master.

14th Commandment: Thou shalt Not Clean Coins!
I think it's in 2nd Leviticus.......
Ok with that said. The Mona Lisa, and the Sistine Chapel have been cleaned.
Proper restoration can be A-OK. But expert or experience work is required.
You can practice on junk coins, and you can read tips, but before anybody touches a "better" coin... please get real help.

Notice in the very first paragraph the author states "With coins that do not have value by condition..." This is the key sentence in the entire article. If the coin has no value due to its condition - nothing you do is going to make it worse. It's already worth nothing.

The author then goes on to say that anything graded higher than worthless - basically don't do anything.

I look at this the same way I do weerdsteev's Buffalo nickel restorations. If you can't see the date, it's basically not worth a thing except as a filler in a type collection (and Buffalo nickels are still cheap enough to keep that from happening). But he takes a dateless nickel and restores the date. Now, IMHO, it would nicely fill a key date hole in my album.

How can you tell if a coin has been cleaned?

What that article talks about is cleaning coins which don't derive their value from condition.

The general rule is, if you can, beyond any reasonable doubt determine a coin has been cleaned, and the cleaning has damaged the surfaces to the extent of a change in grade, then the coin's value will be considerably dropped depending on whether the coin derives its value from date rarity/demand vs condition rarity/demand.

The first half is more important but the techniques use here to answer that cannot be ambiguous in anyway. A natural coin can look cleaned, a cleaned coin can look natural.

E.g.



Semi-mirror fields, hairlines, generally cleaned appearance. This coin has never been touched up, it was simply struck from polished dies.

Or.



Attractively toned, full cartwheel lustre, but extremely fine hairlines on obverse.

Detecting cleaned coins involves learning particular techniques, and seeing the end results in person. I don't believe it's something that can be taught through anything other than experience.

The second point concerns the extent of cleaning. Cleaning wears away the top layer of a coin, if the top layer is already heavily worn, it stands to reason that light cleaning won't cause any relatively significant wear. On the other hand, if you clean a Gem Uncirculated coin, you'll effectively clean away practically any value it may have had.

The effect on value is best determined by the value of a coin in the grade you've worn it down to. Harshly cleaning an Unc coin will probably wear the surfaces similarly to an gVF graded coin, so when it comes to sell it, that's all you can expect. The change in value is inversely proportional to its rarity. A unique 1899-P Half Sovereign, even if it was in pristine condition to begin with, will suffer little loss of value if cleaned, on the other hand an MS68 1960 threepence will drop from a $600 coin to a 60c coin if cleaned.

For more information on cleaning, see:
http://www.numismatics.com.au/Blog/...ons_answered