density of coins?

The following was stated on a group that I belong to:
"When the coin blank gets loaded, inbetween the die faces, it has a certain
size and a specific weight. Once it is "SMACKED" as you call it, with
several tons of FORCE (to imprint the pattern on both sides), certainly the
weight didn't change ---> but the size changed slightly. Thus "the newly
coined - coin has a slightly higher density than its orginal blank..
density (ro) = Mass/Volume.
If volume decreases slightly and the Mass stays constant, then density will
increase slightly.
I don't mess around with graduated cylinders and water. You can if you want.
I size the coin or bar and calculate the volume. It takes a little time but
it gives you a chance to examine the item closely up front and personal
like. If there is any funny business from the merchant -- they start to get
real nervous. You can usually pick up on that.
I will weigh the item. I will even use their scale. I carry a medimum size
nut for a reference. I know the weight of my reference and if that weight
doesn't show up on their scale then there is no sale..
My reference NUT weighs 30 grams which is very close to most coins of the
one ounce variety.. If I am looking at a bar then I carry three nuts."
Could this be true? I have a hard time believing it, even disregarding his
Reply to
Arnold Beland
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I have no doubt that the individual could behave in this fashion.
It has been common in mechanics of metals to refer to the "incompressible plastic flow" meaning that a metal free of voids can be expected to have the same density before and after cold work (like stamping) for all practical purposes.
There are certain caveats... that the pressure doesn't induce a phase change which has a different specific volume, but the phase change is not plastic flow. Another is that the plastic deformation does not induce voids which would be expected to produce a lower density.
Perhaps the focus on "nuts" as portable standards of weight is useful. It would be a common cheap item that one could weigh carefully and carry around to check the scales of the sellers. But, one should carry it protectively, just in case it gets scratched or worn in some way that changes its weight. I wonder to what degree the individual thinks that all nuts of the same commercial size are completely identical in terms of weight. But that is a side issue.
A long time ago, in graduate school, we debated the issue from the standpoint of dislocation stress fields, but reached no clear consensus. Arguments were made for the dislocations resulting from plasticity to both increase and decrease the bulk density ever so slightly. Very tiny fractions of a percent.
Someone may know the status of the concern today, but it isn't me.
Anyway, I don't think that the issue of the plasticity invariance of density has all that much merit to what the "nut" guy actually does in buying or not buying coins.
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My interest in this matter is for the following reason. I have been purchasing gold bullion coins in the form of silver Maple leaf one ounce coins from the Royal Canadian mint. I also have a large quantity of the RCM silver Maple leaf bullion coins. I keep these mainly as a hedge against future increases in the price of silver. I have developed a business of supplying 9999 silver wire to those individuals with an interest in making colloidal silver. I carry this wire in both ten and twelve gauge sizes and have it made in lots of two thousand ounces at a time. I have been following the gradual and seemingly inexorable rise in the price of precious metals. Bullion coins are now available in platinum and palladium as well. I feel certain that more and more people will be interested in in the ownership of precious metals as the various governments continue to simply produce ever increasing amounts of paper money. There are already reports of imitation silver American Eagle coins coming in from China. So far, these are easily detected with a use of a magnet as they are mostly steel. The matter of coins is relatively simple compared to the more common form of precious metals which consists of bars of various sizes, up to one thousand ounces. I am interested in ascertaining the practicability of a device which would use the computational ability of a microprocessor to enable the detection of the purity of these items in a non-intrusive manner. There have been instances of one hundred ounce gold and silver bars being drilled out and filled with lead, topped off, and re-polished. It would seem that recent advances in sensor technology and the processing power of a micro, along with a bit of basic help from our old friend Archimedes should be able to accomplish this.
Reply to
Arnold Beland
Basically, this has a tenuous relationship to the original post.
There are a few individuals here who are qualified to post to the interesting topic introduced above.
Any reason for not having directly brought this up in the first place?
Reply to
I did not elaborate on my reasons for asking the question as I gave no credence to the original statement. You indicate that this can be a factor. I felt that a more detailed explanation of my purpose would help to put the question into context. If there are possible perturbations in the process that are of a value of significance than the whole idea can be simply dropped. I do not think that voids will be a problem with the bars as they are pored.
And now I come across the following which serves to further muddy my waters. Perhaps all this should simply go into the largest trashbin of my mind, the one labeled "it seemed like a good idea at the time".
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Reply to
Arnold Beland
Cold work (embossing coins) decreases density as long as no internal "chevrons" or open cracks are generated, however the greatest possible deformation (ECD Equal channel deformation) introduces at most one atomic dislocation per ten atoms or a overall density change of at most 1% - doing a total uncertainty check using mass and volume determination puts any change in metal density from cold work (coinig) well into the "noise" category for the signal to noise ratio measurement of density.
As far as forgery is concerned - there is no cheap way with "micros" or "sensors" to find the fakes with 100% reliablity - otherwise the government's mints would be using them!
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