Crystals on coin Surface

From:  kavan@lakdiva.org
Date:  Sun Jun 24, 2001  8:33 pm
Subject:  small crytals on coin surface what do they represent ?

I have been looking at some struck copper coins I assume are 
ancient under 17X magnification I can see small crystals on the
side in the crevices. What do they represent, a nice uncleaned
coin or something else I should worry about.

The term "Toning" I assume is used for the change of color of
the surface of the metal and different in character to the
growth crystal, which could not have existed just after a coin 
was struck 

Thanks for any advice or clarification.  I wish there was a 
website with high resolution images of these different results
of real or forged aging.


From:  barnowlc@aol.com
Date:  Sun Jun 24, 2001  10:04 pm

     Such crystals are fairly common on authentic coins. They are also
fairly common in certain types of rocks, some quite recently formed,
where there is a lot of thermal activity or highly saturated water
percolation, or boiling. Metal is leached out of the coin into
solution (such as ground water with carbonic and humic acid in
it). The water hangs around, until the rain or other source goes away
or diminishes. Then the water starts to evaporate. As it does, it
becomes super satured (can not carry all the metal salts or even
elemental metal in solution), so it dumps metal onto the surfaces of
the coins. This tends to happen in cracks because they will often have
more water, where the outside surface can be more sealed in with fine
mud (if water was flowing through very easily, and drying very fast, I
doubt this would happen). Or similar crystals on the surface of the
coin are removed when the coin is cleaned. Tiny nuclei come out of
solution or are recruited from microscopic bits already present, and
you get the standard process as seen in nature often (such as in metal
ores).  

     Such processes are of interest as they can be hard to imitate,
especially if you get to know how they should look. Easy enough to put
crystals of metal on a coin, and it could even be a byproduct of
cleaning processes. I have seen it happen when a cleaning solution
loaded with metal salts dries up over periods of months. I suspect
processes occuring over centuries will be quite distinct from those
occuring over months in the crystalline morphology and other
characteristics.  Copper crystals seem to be the most common type,
even in silver coins. This would be a complex study, and require a lot
of study and review on my part to accomplish much. Still instinct and
experience can be usefull I think with such secondary growths on
coins, to distinguish forgeries from real coins.  

     Most forgeries, if they pretend to be cleaned at all, are not
cleaned over long periods. The forger is usually anxious to get them
to market, as unlike if he had real coins, he has something of no real
value he wishes to profit from, not something he might speculate in
and hold for some longer period.



From:  xtro@netzero.net - Mike S
Date:  Mon Jun 25, 2001  8:54 pm

Electrolytic and even chemical removal of the hard red and green 
patina/encrustations that often form on the surface of debased silver 
such as the tetradrachms of Antonine era Egypt can result in copper 
metal deposits/patches of substantial thickness on the surface. 
Hence, fully metallic (yet ancient) copper can potentially be found 
on authentic silver coins as the result of ill advised cleaning 
attempts. Once done, it is extremely difficult to remove it without 
damaging the coin as well. (Yes, for the record, I have learned both 
these things the hard way!)