Cleaning Coins and Bank Notes
One of the first questions an uninitiated collector usually asks regarding coins they acquire is, “How do I clean them?” The answer is simple: You don't. There is more to this than just the desire of advanced collectors to be purists, demanding that no one has ever retouched the surfaces of a coin. Any cleaning removes some of the surface, even if it is minute and nondetectable to the untrained eye. Furthermore, cleaning involves abrasive cleansers, regardless of how mild these cleansers may be. Cleansers do two adverse things to coins. First, they leave hairline scratches that are detectable under close examination. Second, they will strip the original luster from uncirculated coins.
Once a coin has been cleaned, it may be able to be artificially retoned, however the surfaces are never the same again. There is a difference in surface color that never goes away. This makes the difference between the coin being desirable or undesirable to collectors. Why would a collector purchase a cleaned coin when an uncleaned example is available?
Cleaning coins or notes will have an adverse impact on their desirability and value to collectors. Many a valuable coin or bank note has been ruined by the good intentions of someone who decided the surfaces were in their opinion too dark to be visible, not understanding that collectors would rather have this original color or finish, regardless of if the surface is bright or dark.
Bank notes should never be cleaned either. Washing a note; using an eraser to remove soiling, discoloration, or graffiti; adding tape to a tear; or ironing a note are noticeable and will impact the desirability of the note. A note that has been washed has a different consistency to the paper than before it was bathed, while a note that has been ironed lacks the intaglio relief that should be present because of the ink being ever-so-slightly raised on the paper. All of these efforts to enhance the appearance of a note can be detected and will decrease its value significantly.
In summary, there is no advantage to cleaning coins or notes. The novice may think a coin or note appears to look nicer once it has been cleaned, but to a collector this means the coin or note no longer has original surfaces and as such is of little interest to them.