Hello CFDL,
I think Prokopov et al were the first to publish in any detail
about this method, I wrote more about it after them. Some hints of it
are in other older literature including IBSCC BOCC. I do not claim to
have invented it, though I have independently developed it.
This method works on pressed coins in which the die / mold in
completely filled by the metal, and on cast coins. But only if the
surfaces have not been so degraded by diagenisis or wear, or the
forgers art, that the original surfaces are lost to the point the
surfaces of strike, can not be distinguished from the original
untouched by the dies surfaces. Coins which do not display the
difference, and should, are not struck.
Blanks are safely assumed to not be struck, except in the case
of overstrikes (for most of which the method still will work, just
there will be two sets of borders between the strike and the untouched
by the dies blank). Blanks are generally cast and / or cut, unless
they are previously struck coins struck over.
On a struck coin, there are three areas for the purpose of this
method. The part contacting the obverse die during strike, the part
contacting the reverse die during strike, and the parts which has not
contacted either die during strike.
To use this method effectively, one should gain some experience
and develop some ability. But it is much easier to use this method
once you have read about it, than to develop it on your own (as I
did).
Even low grade coins, will usually have enough of the surface or
subsurface preserved, that thsi method is effective. My advice, if you
see coins burned by acid, heat, very uniform wear (all surfaces
wearing about the same, per Prokopov et al coins usually wear fromt eh
top down, not uniformly or nearly so on all surfaces), until this
method can not be used, then avoid them.
The surfaces of strike will vary in hardness, how mucht hey have
been heated, and the degree of compression. That is, the surfaces
which have actually been hit by the dies. There will pretty much be a
line on each side, one side of that line the blank has been hit, the
other it has not, but sometimes it can be a zone where the coin has
only been hit lightly in the zone.
Dies have very specific effects upon metal. This method is more
often effective for precious metal than base metals, for ancient
coins, but is effective for all types of well preserved coins.
A cast coin, which has not been acid or heat burned, or
abraded on all its surfaces to make them more uniform, will have the
same types of surfaces on all parts. Forget about the morphology and
style of authetnic coins. This method has to do with the quality of
the surfaces, reflecting their microsctructure, not what space the
coin occupies (morphology). Stuck a cast into clay, or a struck coin,
they will leave about the same impression if one is an accurate copy
of the other.
A struck coin, has on the surfaces of strike, specific
qualities. Heating (some struck coins are heated after being struck,
if it is too much, they are probably unauthenticatable), acid baths,
stripping off of the coins surfaces by abrasion (like Prokopov et al
wrote, coins usually wear from the tops down, not at all parts at
once, in nature), over striking / compression, can obscure the
differences between the surfaces where the coin contacted the dies,
and where it did not (or the copy of where it did).
No reason to assume a coin, which shows signs of being doctored
to cover signs of forgery, is an unlucky coincidence of nature, there
are plenty of coins out there which have not been ruined by nature or
circulation.
A cast or pressed coin can transfer from the host many of the
qualities of strike, striations, mint luster (struck luster looks
subtly different than transfer luster), the surface morphology etc...
Casting or pressing alone, can not compress a coin the same way dies
do under great pressure while the metal flows along the dies surfaces.
In a struck coin, on the surfaces of strike, the metal towards
the edges was flowing much faster than at center. Metal near incuses
in the die will also flow faster. In a cast, all the pressures are
about the same, except in a blastcast, in which pressures are much
higher near the entry point for the molten metal spray into the
matrix. In a blastcast where the matrix is worn some from use, the
wear will be much worse near the entry point for the spray (not
something you see in struck coins).
In a struck coin, the dies are polishing and compressing the
metal by pressure, and by motion of the metal along the dies, much as
in a slick and slide (polished rock from a fault, that is movement of
rocks agaisnt eachother under pressure). The mineralogy of the coin is
being altered by the dies, in a manner quite different than in a
pressed or cast coin.
I think a lot of the problem now with pressed and cast coins, is
people are looking at style, and not thinking enough about the
microstructure of the metal, and how it SHOULD look if the coin is
struck. Coin salesmen mostly sell coins, determine prices, and
attribute. These skills are all worthless when using this method, as
is stylistic analysis (if the fake is very good). It is when the dies
matrices or moplds have been recut, that stylistic analysis comes into
play.
People just need to think about coins differently, that is, they
need to learn the new methods, not just cling to old methods whicha re
now worthless against fakes routinely passing those using dated
methods.
Get some coins, and have a look. Even buy a decent blastcast
from one of the many "reputable" venders of them on the net or at coin
shows, and see how it looks different than a struck coin, even to the
naked eye (your vision should be at least average I think).
This is not so hard here folks, a method which does not require
any lab skills at all, not even those that might be seen in a gifted
12 year old, as with hardness tests. We can not take you by the hand
at every step, you have to learn how to crawl, and then walk, on your
own, even if someone helps you along some.
Think about plastic metal flowing along the dies, for struck
versus cast coins (cast coins are liquid filling teh available space,
struck coins are like glaciers in a plastic state flowing to fill the
cavities). Change the way you think, and once you see it, it becomes
obvious enough. If the coin is acid etched and looks like the surface
of the moon under the microscope, why chance it? This method can apply
to base metal coins, but that would be a whole different lecture than
this one.
The fact that the markets are inept as a whole, with isolated
exceptions, about methods such as this, is obvious to any well
informed person. The ship is not repairable, jump ship like a rat, and
start over, and you can pick Mr Markets pockets, instead of having him
pick your pockets with this organised foolishness about letting cast
coins flow into the ancient coin markets freely. Markets are sometimes
foolish, that the ancient coin market is foolish now, should not
really surprise anyone. An ancient coin is either ancient, or a modern
fake of one, nothing really in between, even if it is barbarous. No
ancients either pressed or blastcast coins, so there should be no real
problem here folks.
Just forget all the silliness Mr Market teaches you now in his
especially foolish mood. Youc an not detect decent blastcasts by any
of the sorts of hype going around now, dealers who repeat this hype, I
often see selling blastcasts openly, and in some numbers. A good
blastcasts feels the same to the teeth, to the finernails, has very
similar coefficients of friction etc. as the hsot coin it copied. No,
they do not feel "slick", and they do not have significantly different
thermal properties, these tricks are for other types of casts, not
blastcasts. Blastcasts have the density of the coins they copy as they
are made under explosive pressure, and contrary to possible impression
from Prokopov and Paunov, their composition now can be exactly as with
the authentic coin.
Numismatic crauds have been consistently fooling collectors, and
top name dealers, for at least the last 500 years. So why should
anyone fantasize thinsg are any different today than in the past?
Usually processes act over time in a fairly uniform manner, including
numismatic fraud. There are catastrophes and episodic events, but
things more or less go as as they have. Forgers are sometimes
competent at foolingr reputable markets, authenticators are sometimes
competent at defeating even the best forgeries, just how things have
been, and will continue to be. And sometimes, coin salesmen, in order
to try and make more money, misrepresent their own abilities, and
those of their associates, to defeat the work of forgers and frauds.
Best,
Alan Van Arsdale