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Author Topic: Centration dimples  (Read 3919 times)

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Offline Jochen

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Centration dimples
« on: July 14, 2007, 12:34:06 pm »
Dear forum's members!

I know that this subject is annoying because we have discussed it so many times. But here I have two coins which I nevertheless want to share.

Recently I came across coin #1. It is an AE 27 of Gordian III from Nikopolis ad Istrum, AMNG 2072. It shows clearly the concentric ridges around the centration dimple of the rev.

Seeing these I remembered coin #2, an AE26 of Philipp II  from Tomis, AMNG 3591. Here too you can clearly see the concentric ridges on the rev.

But looking more closely I think these ridges have been made after the striking the rev. because on both coins parts of the devices were influenced or destroyed by these ridges, especially parts of the garment. On the obv. of coin #2 you can see too very dense ridges on the upper part of the obv. which have destroyed parts of the legends. If this would be true then they can't be made before the striking process, I think. But this stands in direct contrast to the prevalent opinion!

Is my view on these coins correct or can you enlighten me?

Any opinion highly appreciated!

best regards

Offline slokind

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Centration dimples
« Reply #1 on: July 14, 2007, 02:28:36 pm »
This cannot be decided theoretically without experiment, but I think that ridges on the flan, left by turning (using something lathe-like or drill-like with an attachment)--the still visible ridges, in any case, could survive in certain cases both the flattening (in the field) and the low relief (of the figural intaglio in the die) and appear as, especially on the lower drapery of your second coin, continuous.  Why would striking affect the deeper-lying field LESS than the actually less impacted figural areas?
Perhaps a Bulgarian friend could direct you to a Bugarian with a suitable anvil who had access to some cast dies, provided you guaranteed anonymity!
Pat L.

Offline Akropolis

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Centration dimples
« Reply #2 on: July 14, 2007, 02:47:17 pm »
Jochen writes: "because on both coins parts of the devices were influenced or destroyed by these ridges, especially parts of the garment."

Perhaps the devices were not "destroyed" by the ridges. I think this phenomenon could be explained by a slightly concave surface at that point and the coin was not fully struck-up. See image below for a larger and similar defect in striking.
Just my opinion.
PeteB

Offline Jochen

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Centration dimples
« Reply #3 on: July 14, 2007, 06:43:57 pm »
Thanks for your postings! I think your explanations are plausible!

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Offline Johnny

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Centration dimples
« Reply #4 on: August 22, 2007, 03:58:49 pm »
I actually have a little experiment on the go involving dies and manufacturing coins,  I'll see if I can reproduce this .

Offline Jochen

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Centration dimples
« Reply #5 on: August 30, 2007, 05:40:05 pm »
Sorry, here is a new one which bothers me again:

Nikopolis ad Istrum, Gordian III, AMNG 2048
Demeter stg.l., holding grain-ears and poppy in r. hand and long torch in l. hand.

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Offline curtislclay

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Centration dimples
« Reply #6 on: August 30, 2007, 06:09:34 pm »
Jochen,

The flan was first smoothed, creating the concentric furrows, then struck with the dies, but the rev. die was not driven hard enough into the flan at the top to eradicate the furrows.  Note the weak N of the ethnic at 12 o'clock, a result of the same weak striking.

Apparently the engraver left out the R in P - OC IC at end of rev. legend.  Doubtless the same rev. die as AMNG 2048, where Pick also couldn't find the R!
Curtis Clay

Offline slokind

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Centration dimples
« Reply #7 on: August 30, 2007, 11:23:16 pm »
At the same time, what a great image for How to Make a Tall Torch (not that they necessarily were all unifrom, of course).  Pat L.

Offline PeterD

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Centration dimples
« Reply #8 on: August 31, 2007, 07:36:50 am »
And yet looking at these pictures it's difficult to escape the conclusion that the dimples and rings were created after striking. On the last coin for example, the furrow across Demeter's head appears to be just as deep as it is in the field. On most of these coins, the dimples and circles appear on high points -such as in the middle of a bust. Looking, for example, at the bust on the first coin that Jochem posted, surely the die is worn, rather than being a weak strike as detail in the middle of the bust (hair etc.) is missing whereas details round the edges of the bust are present. Nevertheless the 'movement of metal' is greatest at centre of the bust and I would have thought the pressure at that point would be sufficient to eradicate any furrows and dimples. In fact on the reverse of that coin, the dimple seems to have a raised rim, which should not be possible.

Just my opinion.
Peter, London

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Offline Heliodromus

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Centration dimples
« Reply #9 on: August 31, 2007, 08:39:11 am »
Peter,
It's true that more metal needs to be moved to create the raised bust, but the raised area (= recessed die area) is also going to have the least flan contact on a weak striike (the flan won't be sufficiently "pushed into" the die to contact the most recessed areas), so it's to be expected that these flan furrows would be preserved there.

Ben

Offline PeterD

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Centration dimples
« Reply #10 on: August 31, 2007, 08:49:46 am »
Peter,
It's true that more metal needs to be moved to create the raised bust, but the raised area (= recessed die area) is also going to have the least flan contact on a weak striike (the flan won't be sufficiently "pushed into" the die to contact the most recessed areas), so it's to be expected that these flan furrows would be preserved there.

Ben


Yes, that's true. My brain must be working upside-down today. :)
Peter, London

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