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Author Topic: Machine cut modern dies  (Read 4699 times)

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Offline glebe

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Machine cut modern dies
« on: October 28, 2012, 08:03:58 am »
According to Prokopov saw tooth edges on letters (especially) such as those shown below are markers of machine cut dies. This image (amongst others) can be found here:

https://www.forumancientcoins.com/fakes/displayimage.php?album=16&pos=13

However I'm not sure that Prokopov is correct. I would expect a modern multi-axis cutter to produce neat parallel equi-spaced sawtooth markings (aligned in only a small number of different directions), whereas what we invariably actually see is a messy collection of teeth marks in all sorts of different directions.
This last is exactly what I would expect from an ancient die cutter, who would cut small tight curves with a chisel tip as a series of short gouges along the line of the curve.
On the other hand it seems odd that this sort of pattern seems to be found only on certain types of coins, notably the earlier Byzantine gold issues, which are of course flooding the market these days. If Prokopov is correct then many, and possibly most, of these coins are fakes.

Ross G.

Offline Joe Sermarini

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Re: Machine cut modern dies
« Reply #1 on: October 28, 2012, 08:18:48 am »
I am also not sure he is correct.  Perhaps there is something that differentiates modern machine cut from ancient hand cut that look similar. 
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marrk

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Re: Machine cut modern dies
« Reply #2 on: October 28, 2012, 09:09:12 am »
I think by engravers knife, chisel

Offline Matt Inglima

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Re: Machine cut modern dies
« Reply #3 on: October 28, 2012, 12:50:32 pm »
Wouldn't ancient engravers have used premade letter punches to create inscriptions? 

Offline *Alex

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Re: Machine cut modern dies
« Reply #4 on: October 28, 2012, 02:20:39 pm »
Punches do seem to have been used, but not always letter punches. Although individual letter punches probably were used at times, it appears that the letters sometimes have been made up from a small variety of punch shapes - an I shape being used for letter uprights in, for example, E F H K L M N P R V,  which is why you often see V's looking like H's or two I's.


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Offline glebe

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Re: Machine cut modern dies
« Reply #5 on: October 28, 2012, 07:41:15 pm »
Actually, on a curved line made by a modern cutter the serrations would presumably not be parallel (as the die would be turned against the cutter), but they would at least be neat and regular, which is not what we typically see in ancient coins.  
Also the step size on the coins is around 0.1 mm (100 micron), while the resolution of cutting machines seems to be a lot better than that.

Ross G.

Offline marcos x

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Re: Machine cut modern dies
« Reply #6 on: October 28, 2012, 10:55:49 pm »
prokopovs pic looks like result of rotary dremel blades being used to cut a die.
when I die make sure to put two coins on my eyes for the boatman......make sure they are not fouree's

Offline glebe

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Re: Machine cut modern dies
« Reply #7 on: October 28, 2012, 11:13:34 pm »
prokopovs pic looks like result of rotary dremel blades being used to cut a die.

Interesting idea - it might add the necessary element of crudity. Or a dentist's drill perhaps - more power.  I suspect though that these would give a more fine grained result than we actually see - maybe someone could try cutting a few letters on (say) a bit of brass for us using these gadgets.

Ross G.

Lloyd Taylor

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Re: Machine cut modern dies
« Reply #8 on: October 29, 2012, 02:16:52 am »
However I'm not sure that Prokopov is correct. I would expect a modern multi-axis cutter to produce neat parallel equi-spaced sawtooth markings (aligned in only a small number of different directions), whereas what we invariably actually see is a messy collection of teeth marks in all sorts of different directions.
This last is exactly what I would expect from an ancient die cutter, who would cut small tight curves with a chisel tip as a series of short gouges along the line of the curve.

I think it would help if you either put a scale on the image, or think of the scale of what is shown in the image.  

The tool marks are at far less than tenth of millimetre scale ( I estimate ca 10 microns or less), far smaller I suggest than that capable of being produced by any ancient engravers tool (at least any one of which I can conceive as applicable to the technology of the time).

Offline quisquam

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Re: Machine cut modern dies
« Reply #9 on: October 29, 2012, 02:38:10 am »
Assuming the letters COMOB are approximately 1 mm high on a Tremissis the chisel marks are approximately 0,05 mm (50 micron) apart on the coin pictured,  if my calculation is correct.

Stefan

Lloyd Taylor

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Re: Machine cut modern dies
« Reply #10 on: October 29, 2012, 02:48:02 am »
Its not the spacing but the actual edge dimension of the of the tool mark I am referring to. The latter defines the edge precision of the tool. Even if we take the 50 micron estimate (1/20th mm) does it alter the substance of the argument?  I think not!

Offline quisquam

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Re: Machine cut modern dies
« Reply #11 on: October 29, 2012, 03:07:56 am »
I think the dimensions of the marks are not too small for a hand guided tool. And they don't look machine made to me.  That's just my personal opinion, of course.

Stefan

Offline jmuona

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Re: Machine cut modern dies
« Reply #12 on: October 29, 2012, 04:59:41 am »
I have not made any new pictures, so I do not know how well this holds, but...
When I looked at 1st century coins under high magnification, I noticed there were "clean-cut" letters and ones that look like the object of this discussion. The only one I could find immediately (I have 220 GBs of images) is the one attached here, a definitely genuine Domitianus denarius. Look at the letter "O" in POT. There are similar marks there as well.
s.
Jyrki Muona

Lloyd Taylor

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Re: Machine cut modern dies
« Reply #13 on: October 29, 2012, 06:56:21 am »
...., I noticed there were "clean-cut" letters and ones that look like the object of this discussion. The only one I could find immediately (I have 220 GBs of images) is the one attached here, a definitely genuine Domitianus denarius. Look at the letter "O" in POT. There are similar marks there as well.

Superficially similar but far from the same and of entirely different origin. Notice that these marks are only on the outside of the letters adjacent to the circumference of the coin and that they align with flow lines directed to the outer edge of the coin. They are the result of die wear/erosion due to the flowage of metal at high pressure and temperature from the engraved letters (locally die high points which focus the striking force in the struck metal) toward the outer edge of the die and coin during repeated striking. They are identical in origin to flow lines which are a manifestation of die wear -  thus they are not the result of tool marks left by the engraving process.

Offline Hydatius

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Re: Machine cut modern dies
« Reply #14 on: October 29, 2012, 09:39:51 am »
It looks as though its from the reverse of a solidus. I'd want to see the entire reverse before I could judge whether it was a fake or not.

Richard
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Offline PeterD

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Re: Machine cut modern dies
« Reply #16 on: October 29, 2012, 12:30:02 pm »
Actually, on a curved line made by a modern cutter the serrations would presumably not be parallel (as the die would be turned against the cutter), but they would at least be neat and regular, which is not what we typically see in ancient coins.  
Also the step size on the coins is around 0.1 mm (100 micron), while the resolution of cutting machines seems to be a lot better than that.

Ross G.

The resolution quoted is the accuracy of the machine in engraving, say, a line at a certain position. This is effectively the resolution of the stepper motors moving the cutter over the work. Engravers use a rotating cutter. It is the diameter and profile of the cutter which would govern how accurately a die could be made (or rather how inaccurately since real ancient coins do not follow an exact mathematical profile). Of course, any tool marks would be horizontal and circular. Routers and CNCs also use ratating cutters.

Of course there is laser engraving. I don't know if it would work on metal. I rather think not.

I tend to think that forged dies are not made with any type of engraving machine. It may be that a rough design could be made with a hand-held engraver - someone mentioned a Dremel - and finished with off in the old-fashioned way with a narrow-tipped chisel. But then that should not look any different from an authentic die.
Peter, London

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Offline Hydatius

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Non tam praeclarum est scire Latine quam turpe nescire.

Offline quisquam

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Re: Machine cut modern dies
« Reply #18 on: October 30, 2012, 09:24:48 am »
You seem to be familiar with this type of Basiliscus. What do you think: modern dies or transfer dies?

Stefan

Offline maridvnvm

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Re: Machine cut modern dies
« Reply #19 on: October 30, 2012, 09:46:46 am »
What would you make of these letters in this context?



Martin

Offline quisquam

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Re: Machine cut modern dies
« Reply #20 on: October 30, 2012, 10:02:49 am »
 It's the same phenomenon as shown by Mr. Prokopov. To my mind these are chisel marks, caused by frequent gentle hammer strikes against the chisel, which don't have to be modern.

Stefan

Offline Hydatius

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Re: Machine cut modern dies
« Reply #21 on: October 30, 2012, 05:51:21 pm »
modern dies

Your reasons?

Ross G.

Neither obverse nor reverse looks anything like the real thing, of which I attach two photos below, both from the mint of Milan.

Richard
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Lloyd Taylor

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Re: Machine cut modern dies
« Reply #22 on: October 30, 2012, 06:35:12 pm »
Image 1: High precision cutting tool marks on incuse (die equivalent) edge letters of a modern coin. Normally these are polished out on a finished die so not in evidence on the minted coin. However for for incuse lettering on the edges such is not the case.

Image 2 & 3: lower precision cutting tool marks on the incuse letters/design of many counterfeits of modern coins - use this sort of lettering on a die and don't polish out the engraved elements and you get the tool striations at the scale in evidence on the "dubious ancients".

The regularity and consistency of the spacing of the tool marks on discrete letter elements (it will differ from element to element depending on cutting tool orientation wrt the design) points to modern origin, rather than ancient chisel marks, which would show far less consistent spacing on each design element (all other considerations against the ancient chisel mark argument aside). As Peter notes...
The resolution quoted is the accuracy of the machine in engraving, say, a line at a certain position. This is effectively the resolution of the stepper motors moving the cutter over the work. Engravers use a rotating cutter. It is the diameter and profile of the cutter which would govern how accurately a die could be made (or rather how inaccurately since real ancient coins do not follow an exact mathematical profile). Of course, any tool marks would be horizontal and circular. Routers and CNCs also use ratating cutters.

In my opinion the clue to the situation  is to be found in this statement
On the other hand it seems odd that this sort of pattern seems to be found only on certain types of coins, notably the earlier Byzantine gold issues, which are of course flooding the market these days. If Prokopov is correct then many, and possibly most, of these coins are fakes.


Offline glebe

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Re: Machine cut modern dies
« Reply #23 on: October 31, 2012, 02:27:25 am »
Indeed, the Basiliscus tremissis does look more than a little suspicious, as does the Anastasius. But even if the dies in these cases are modern, I can’t agree that the letters are machine cut, or even cut with a mechanical engraving device of some sort – to me they are simply too uneven, and for the moment I have no reason to doubt that they were cut (i.e, gouged) with a simple chisel, rather than a modern tool. Which is of course the kind of technique that ancient cutters could also have used.
As to the incidence of serrated letters and curves in ancient coins, the pattern is not simple. This feature is common with Constans II gold issues in the 7th century, as here:

[LINK REMOVED BY ADMIN]

(you may need to blow the image up) and there are plenty more like this in the CNG archives, for example. On the other hand serrations seem to be absent from (say) Anastasius II coins in the 8th century (where curved letters seem to have been drawn as short arcs). It should be noted that the style of the Constans II’s on offer these days is otherwise impeccable, with examples from a large number of dies.
In earlier times serrations are not so common, but they do occur, in (e.g.) this Anastasius I tremissis:

[LINK REMOVED BY ADMIN]

and in fact in this Basiliscus solidus:

[LINK REMOVED BY ADMIN]

which to me at least looks genuine (although these types are not my field).
These various coins are also shown below in the same order.
On the whole I’m not yet convinced that we have to assume that serrations (and particularly the irregular serrations that we actually see) necessarily mean modern fakes.
But if they do then there are serious consequences. Collectors (and resellers) should be asking for their money back, and an awful lot of these types have been, and are still being, sold in recent years, many, in the first instance, by the major auction houses. (It would of course be interesting to know where all these 6th and 7th century solidi are coming from in the first instance, but nobody’s likely to tell us. The rumour is a large find which is now being exported from Syria, but if they are fakes this may just be a cover story).

Ross G.



Offline quisquam

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Re: Machine cut modern dies
« Reply #24 on: October 31, 2012, 02:54:15 am »
Thanks for the pictures, Richard. I haven't seen examples of RIC 3310 before.

If the marks shown by Mr. Prokopov are the result of modern machines for transfering the matrix of an authentic coin into a new cut die (that's the way I understood his article), then this marks on a fake from modern dies don't make any sense to me. If this marks are caused by a hand guided tool (hammer and chisel for example), they perfectly make sense, on a fake from modern dies, on ancient coins, on fakes from transfer dies and on 'good' cast fakes.

The eastern denarius of Septimius Severus(?) shown by Martin is another reason for me to think, that these marks don't have to be modern.

Stefan

 

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