Thanks for the help. I do have the A.N.A's grading and counterfeit
detection videos, and have seen the specific gravity test
demonstration. I figured that there was a machine to do it with, but I
guess I was wrong. Thanks for responding to my e-mail.
Also, I do not post in this group very often, but I just thought I'd
let you know that I enjoy reading your comments on various coins on
Ebay. They are very educational! Thanks!
On Monday, May 5, 2003, at 03:10 PM, Mike Diamond wrote:
> Hi Jon. As far as I'm aware, there is no "machine" for doing
> specific gravity tests. You've got to rig up an apparatus for each
> balance. Since the design of balances vary (e.g., platform vs.
> basket), the apparatus must be tailored to the particular design.
> In principle, doing specific gravity is simple. You need to suspend
> your coin by some kind of clip or support and immerse it in a
> container of distilled water which is independent of the balance.
> You are checking the "before" and "after" weights of the coin,
> establishing its relative bouyancy/density.
> In practice, establishing specific gravity can be difficult. You
> need a balance that is accurate to at least the nearest 0.01g,
> preferably the nearest 0.001g. You need to subtract the weight of
> the clip in doing your calculation, which is not too hard if you
> can "zero" the balance after each step. The tiniest bubble adhering
> to the coin or the clip can throw off your results. A measurement
> error of only 1-2 hundredths of a gram can erase the difference in SG
> values between silver and copper. Getting reproducible and
> repeatable results is often difficult.
> J.P. Martin, in his video "Detecting Counterfeit and Altered U.S.
> Coins", demonstrates a good design for a coin support and shows how
> SG testing is done. It's available from the ANA. Members get it for
> a reduced price.
> --- In email@example.com, Jon P. Sullivan
> <errcoins@b...> wrote:
> > Hi,
> > does anyone here know where I can get the machine for taking
> > gravity tests? I would very much appreciate any help!
> > Thanks
> > Jon
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