Cleaning Coins

When dealing with new collectors and less experienced hobbyists, the subject of cleaning coins comes up with almost clockwork regularity.  I wrote an article a few months back about but it was short and did not explain things in depth.  The subject came up again recently so I went ahead and made it the topic of a Coin Class video.

First General Rule: Don't Clean Your Coins

THE FIRST THING THAT WASHES AWAY IS NUMISMATIC VALUE

Without getting into detail, this is a rule that is based on the experience of millions of collectors that have come before you.  We've tried it all.  The expected result is a coin that is reduced in value as a result. 

It may be that you will have to try it for yourself to learn the lesson.  If this be the case, then get right in there and get your hands dirty.  I suggest trying it on some circulated Memorial Cents to get a feel for cleaning coins, see how it's done, and what it entails.  Rather than risk a valuable or favorite coin the first time out of the gate, practice with a coin that already has no numismatic value.  If you ruin the coin, it won't matter.

Try everything.  Ask people what they use.  You'll get every answer from soaking in ketchup to using a blowtorch.  Lemon juice, coca-cola, toothpaste, pencil erasers, dawn, copper cleaner, metal polish, borax, laundry detergent, xylene, mineral spirits, WD-40, acetone, ammonia, bleach, denture cleaner, eye drops, Alka-Seltzer, alcohol, Windex, milk, MEK, gasoline, olive oil, and some stuff I aint never heard.
I recently called the museum down at the University of Gainesville:

"I heard on facebook that ketchup is the best way to clean antique coins and historical artifacts and I was wondering what brand you would recommend."

I can't believe they hung up on me.

Cleaning is not the same as Conservation

Conservation serves to preserve historical artifacts without damaging or altering the item.  Learning proper conservation techniques will require years of study.  You won't learn these techniques in a facebook post, a 5 minute video, or a short blog post.
Considerations include the surface of the object, reagents and solvents, debris identification, understanding the potential interactions of the reagents and solvents with that debris, oxidation and reduction chemistry, metallurgy, vapor and contaminant control, tools and how they react with the agents, and environmental equipment necessary for controlled exposure and treatment of the surfaces involved.

Cleaning a coin removes 2 things, debris and value.  It will not restore the coin to its original appearance.  It will not bring out its original luster.  More often than not it will alter the surface of the coin in a manner that will forever destroy numismatic appeal.  An experienced collector can tell at a glance if a coin has been cleaned.  The way the coin reflects light is changed because the surfaces have been changed.  While a cleaned coin may be bright, it will not offer the same cartwheel effect as when originally minted.

The cleaning methods listed above generally fall into 3 categories:

Abrasives
Pumice, fibers, grit, sand, and fine hard materials are added to cleaning products to scour a surface much like sandpaper scours paint from the hood of your car.  These abrasives damage coins by scraping and gouging fine marks into the surface, diminishing details, and removing metal.

Acids
Ketchup, lemon juice, vinegar, and Coke contain acids.  Phosphoric acid, citric acid, acetic acid, and more complex organic acids will interact with metals.  Copper is especially affected as it is prone to reaction.  These acids can etch the surface, promote oxidation, and leave permanent discoloration.  In more extreme cases of acid exposure the surface can be pitted and corroded.

Solvents
These are compounds which readily draw other materials into solution.  Materials are dissolved.  Not just the material on the coin, but the metals of the coin itself.

Surfactants
Soaps and detergents act as surfactants, changing the properties of the solution in which they are mixed.  These are great at getting the grass stains out of cotton, but we're not really talking about grass stains or cotton.  The issue here is removing the surfactants from the coin which usually requires an abundance of water (a solvent), bringing exposure to whatever compounds are already in the water: chlorine, flourine, salt, acetohalenes, calcium, iron, and whatever else can be found in wells and municipal water systems.  Incomplete rinsing can leave behind a film which, over time, can further damage the surface of a coin.  You get one thing off but you add another.

For all the effort and expense involved in cleaning a coin, it's a sad result to learn that the value of a coin is reduced.  Experienced collectors have little interest in coins that have been cleaned.  Cleaned coins are dull, damaged, stained, spotted, pitted, corroded, scratched. streaked, lackluster, discolored, and altered.  It is true that a cleaned coin can develop a new tone after many years but this tone is unlike naturally toned coins and again, an experienced collector can identify a retoned coin at a glance.
The reduction in value can be complete, reducing a coin to its metal value or face value.  For some better dates the reduction in value may not be complete but can still be considerable, with specimens fetching less than half of the market value of an uncleaned coin.  It's a crying shame to learn the coin you thought was worth $500 was reduced to $50 because you cleaned it with toothpaste 20 years before when you were just getting started in the hobby.

Grading companies such as PCGS and NGC won't extend their certification guarantee to cleaned coins.  Sometimes they will return them ungraded and unslabbed.  Sometimes your coin will get a Details rating which is akin to writing "Junk" on it with a crayon, and they still keep your 50 bucks.

If grime is a concern there are ways to deal with the grime without ruining your coins.  Latex gloves can be purchased locally for a few bucks.  These will protect your hands.  You can put down a towel on your work surface to keep it clean.  When you are done examining your coins, throw away the gloves and towel, wash your hands.  Let that grime go down the drain rather than the value of your collection.