Valuing Cleaned Coins - Is There A Method?

That says it well.

NGC price guide is a handy way to do some comparisons. Under MS60, AU50, etc they list auction prices for Details coins alongside the straight-graded. As mentioned above, lots of variables. A cleaned coin that would have been MS64 otherwise may have sold for more than a regular MS60, someone could have cherrypicked a scarce variety, etc.

Post the coin you're curious about.

Not a bad analogy, just take it to the next level!

For most, it all comes down to eye appeal, and everyone has their own tastes. This is why we say buy the coin, not the slab/holder. Ignore everything written on a coin holder (whether a slab or a dealer's 2x2) and just look at the coin. You usually know when you like a coin or not. Then you have to figure out a price. Grade it to the best of your ability, knock points off for cleaning if it helps for checking price guides. No harm in making an informed offer.

I too say that.

My Rule:
1. Grade the coin as if were not cleaned.
2. Find the value for that grade.
3. Cut that value in half.

Jcassidy- Sounds interesting, let's see some before and after photos of these successful coins.

To answer the OP's post: the difficulty in assigning a hard and fast rule for valuing a cleaned or otherwise damaged/ungradable coin is the reason why the TPGs don't "net grade" such coins; net grading would imply the TPGs have an official opinion on how to value a cleaned coin, which they do not and can not have.

My personal rule, for consideration: when you look at a "badly cleaned coin", consider how long you'd need to use it as a pocket piece before the evidence for the cleaning is worn away. How worn would the coin be at that point? Then assign a grade to that level of wear, and look up the price of the coin in that grade. That is it's "cleaned value".

As for jcassity's points, let's deal with a few of them.


Um, no. For starters, coins are made of toxic heavy metals. Biological agents do not readily grow on coins, and any that do find themselves living on a coin can easily be washed off in water, no other chemicals required, because biologicals are completely unable to "take root" in dry metal.


Absolutely. The problem is in doing that "untraceable cleaning". Acetone is one such untraceable method. Distilled water is another. Acids are not. Whizzing is not.

We already have this. "Market acceptable cleaning", like water or acetone, is straight-graded by the TPGs. No need for marking such coins as "restored". A difference that makes no difference is no difference, and these market-acceptable cleaning methods don't make a difference to a coin's condition.


Ultrasonic cleaning is a wonderful method for cleaning coins, in theory. The problem always comes down to the practical application of that theory. Specifically, how to suspend a coin in the cleaning solution without it touching anything. And I do mean anything - the coin needs to levitate in the water. The bottom of the bath, any rack the coin sits on, or even a piece of string tied around it, will be a friction point. As the coin rapidly moves back and forth due to the ultrasonic waves, anything it is touching will be a small friction point - a wear point.


Phosphoric acid is, of course, the reason why Coca-Cola "works so well" at cleaning coins. At that ratio, you're using a solution at about 1.3% phosphoric acid - that's over 20 times stronger than Coke (about 0.05%), though of course fizzy Coke has dissolved carbon dioxide (carbonic acid) in it as well, making it more acidic (only about half of the acidity in fizzy Coke is due to the phosphoric acid).

Sonication removes physical dirt and grime by creating microscopic bubbles on the surface of the coin, which then implode. You would normally need a surfactant (soap or detergent) to get these microbubbles to form, but when metal is dissolving in acid, the bubbles come from the hydrogen gas generated as a byproduct of the chemical reaction. The acid would do this work just fine without the sonciation, but the sonication would help the acid to dissolve the coin much faster.

I would strongly suggest you avoid the acid.


Um, no. Nether phosphoric acid (H3PO4) nor acetone (CH3COCH3) are similar to water (H2O), though if anything, acetone is closer to water in terms of chemical and physical properties: both acetone and water are polar solvents, which is why acetone is completely soluble in water. Phosphoric acid is an inorganic acid and as such strongly ionic; it doesn't have "molecules" in the same sense that water and acetone do.

In terms of origin, both of them come from rocks. Acetone is normally derived from fossil fuels (as a byproduct of phenol production), but it can be produced biologically (during WWI the British pioneered industrial-scale acetone fermentation, to help them make explosives while oil shipments were restricted under German U-boat blockade). Phosphoric acid is made from phosphate rock.


Um, no it won't. Acetone cleaning, if done properly, leaves no trace; the acetone evaporates away quite quickly and completely in normal conditions. What might leave a trace is improper (or, if you like, "unfinished") acetone cleaning, where the acetone has washed off the organic goo as intended, but has then evaporated away, leaving behind a thin film of "goo" all over the coin. The answer here is not avoiding using acetone, but rather, using more of it. After the acetone soak, a coin needs several "rinses" in fresh acetone, to wash off the contaminated acetone before it dries. Some people advocate a final rinse in deionized water but this is redundant; anything that four rinses with acetone might still leave on a coin isn't going to come off in water. But, a DI water rinse can't hurt either, so if it makes people feel better, go ahead and water-rinse.

The main problem with acetone (besides the whole "highly flammable" aspect) is contamination. This contamination doesn't usually come from the acetone itself, but from whatever it is that you're using to dunk the coins in and out of acetone. You shouldn't use your bare fingers, because acetone sucks the oil right out of your fingertips and that oil can then get deposited onto your coin. And many types of plastic or rubber will depolymerize and dissolve in acetone, so if you use rubber gloves, they need testing to ensure they're acetone-resistant. Glass and metal objects are safer, though of course you have to be careful not to scratch the coin when using these; cellulose-based items (paper, cardboard and pure cotton) are also acetone-safe.