Using weight to positively identify coins

kranky

There was an interesting article in CW that proposed the use of very accurate weight information as a way to identify specific coins even after they become toned (or untoned, as the case may be!). The author suggests that a coin's weight in grams to four decimal places is sufficient to identify a particular coin over time. This method could be used to track coins for pedigree purposes.

He went so far as to calculate the additional weight that toning would add (did you know blue toning is the heaviest?), showing that it would not affect the weight within the four decimal places.

This method obviously requires a highly accurate scale, and such scales are available for under $2000. This is no doubt out of hobbyist range, but considering you can get them with RS-232 interfaces which would connect directly to a computer, it would certainly be appropriate for, let's say, a major third-party grading service. The interface would make it trivially easy to record weights in a database and even put on the label if desired, and could be a good selling point for being able to positively identify coins over time for pedigree tracing or other purposes.

richbeat

As Arte Johnson would say, "veeeeeerrry interesting."

mgoodm3

But, given only 4 decimal places, there are only so many weights for many more coins, there will be repeats. But, the chances of two similar coins having the same weight is small, but not 0

mgoodm3

They should add identifying marks on the coin also. That's what they do with diamonds.

sinin1

what would the purpose of this be?


I bet you if I dip a toned coin - with the color and a little of the surface on the coin, it will weigh less than it did before


and definitely more than 0.0001 grams less

dorkkarl

tough to weigh coins in slabs

K S

geb209

Weight would definintely change over time. How could it ever work?

kranky

The author believes that the weight of a coin is indeed stable, even allowing for eventual toning which may occur.

hookooekoo

Given that we are talking about accuracy that can almost detect the weight of toning, I would have to agree that the weight of the coin is going to change. Simply touching the coin will change it's weight by either adding oils and dirt from your skin, rubbing off dirt and contaminates, etc.

But the concept is still valid as another way to help identify the coin. Just like using marks to identify a particular coin (which can change as the coin is handled), weight is another way to HELP identify a coin.

1jester

0.0001 gram is an extremely small increment. I have an electronic scale that's accurate to 0.01 grams, and that is so accurate that I can't seem to use the information. I mean, how much weight does a coin lose through normal circulation??

I hope TPGs, if they decide to use this method, also make sure they balance and calibrate their scales frequently.

sinin1

I would think just different humidity and condensation of water from the air would change the weight of the coin probably more tha 0.0001 grams on a weekly basis

Does this guy recommend storing your coins in a vacuum chamber?

hookooekoo

I remember using those scales (accurate to 0.0001 grams) in chemistry class in collage. They are so sensitive that air blowing accross the scale can change the reading (hence why these scales have doors to enclose the item being measured).

But again, scales could be used as a tool to HELP identify a coin. For this to become a helpful aid, it would be necessay to first study hundreds of coins so that you could learn the distribution of weights (i.e. what is the average difference in weights of similar coins) and how much the weight of a coin varies over time because of handling (because of body oils and dirt).

I would think just different humidity and condensation of water from the air would change the weight of the coin probably more tha 0.0001 grams on a weekly basis

condensation on my coins!!! Don't want that...
but seriously, I don't think humidity would have much of an effect the measurements, other than how it might effect the operation of the machine. The metal of the coins wouldn't be absorbing water from the air (like say a piece of paper might).