What's wrong with cleaning coins?
It is a question that has been debated in numismatic circles for decades, while there are many points to either side of the debate, at the end of the day, most forms of cleaning destroy the top layer of the coin in order to reveal the bright surface below. While many argue that this is a microscopic level of damage and therefore insignificant, it has macroscopic consequences to the same degree as circulation wear.
A genuine uncirculated coin is best defined as an unworn coin with its original surfaces intact.
In extremely fine a coin will have its original surfaces in the devices but its exposed surfaces will only have partial originality having suffered from circulation wear (roughly 1-3 years of circulation depending on the alloy).
In very fine a coin will have practically no originality in the exposed surfaces having suffered from extensive circulation (roughly 5-15 years of circulation depending on the alloy).
A typically cleaned (wiping down with a cloth), but otherwise uncirculated coin will have similar surface damage to an extremely fine graded coin, i.e. after 5 minutes of cleaning, the coin can suffer to a similar extent as 3 years in circulation!
A harshly cleaned (wiping down with a brush), but otherwise uncirculated coin will have similar surface damage to a very fine graded coin, i.e. after 5 minutes of cleaning, the coin will suffer to a similar extent as up to 15 years in circulation!
These figures are calculated by measuring the microscopic damage through how light reflects off the coin. See our article on lustre to find out how this works.
While the damage may be microscopic, the visible effect of destroying the coin's lustre will make an Uncirculated coin look as low as very fine to the trained eye. Any dealer worth his salt would pick up that the coin has been cleaned and if you're looking to sell, the dealer would offer you a significantly lower figure, or if they're like us, they'll refuse to buy your coin at any price!What is the value of a cleaned coin?
The effect of cleaning on a coin's value is highly dependent on where the coin derives its value from. For example, cleaning a poor condition 1813 dump will have very little effect on the coin's value as most of its value derives from its rarity. On the other hand, cleaning a Gem 1938 florin will knock its value from $800 to $10 as most of its value derives from its quality (which is what cleaning attacks).
Take this uncirculated 1931 half penny that we sold on eBay as an example:
Sadly not all dealers are honest enough to declare when their coins have been cleaned.I'm about to buy a coin, how do I know if it has been cleaned?
It would take a 2 inch book to teach about detecting all the common methods of coin cleaning so rather than teach detection techniques, here are a few simple precautions:
One of the arguments that coin doctors try to make is that the whole cleaning coins debate is about black vs white coins. That being, naturalists like black coins, and the coin doctors like white coins. This is just not true and the debate actually surrounds the damage done by cleaning and the natural appearance of a coin (see our article on lustre to learn about the most important quality of a natural coin) rather than the end colour of a coin.
In fact, many times a brilliant, white silver coin can be natural (for example, 1910, 1925, 1931, 1935 and 1936 florins are all available in a bright white due to the bank rolls found of each date), while cleaned coins eventually re-tone. In fact, the destruction of the top layer of a coin through cleaning destroys the coin's lustre which provides a natural illumination beneath a toned coin, so coins toned completely black have probably been cleaned (though not always the case).
The simple question I propose to coin doctors (you know who you are), if collectors really like cleaned coins, why don't you declare that your coins have been cleaned rather than trying to silently pass them off as natural coins?Who are these so called coin doctors?
As a fellow coin dealer, it wouldn't be my place to name and shame other dealers but one good tell-tale sign is opposition to third-party grading (PCGS or NGC). While there are some legitimate arguments against them, I've found that most of the dealers that oppose third-party do so because they don't want their customers certifying their coins only to find that they've been cleaned.What about restoration and conservation?
Restoration and conservation is another matter all together. In general, this is done to preserve the life of a coin, such as removing verdigris to prevent further corrosion. While generally an acceptable practice, the issue is that many dealers will then try to sell a coin without declaring the work done. Most of this revolves around removing corrosive elements from the surface of a coin and while if caught early enough, can be done without any significant damage, most of the time it will leave the surface pitted at the microscopic level (which can be difficult to detect without the right equipment).
In the end your best defence is to stick with certified coins while you learn the intricacies of grading and detecting doctored coins.