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Ptolemaic Bronzes - Central Depression

 
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Bedrock of the Community
Australia
18966 Posts
 Posted 10/13/2013  10:32 pm Show Profile   Bookmark this topic Add sel_69l to your friends list Get a Link to this Message
I have never read about a reason for these, other than the suggestion that they assisted in the manufacture of these coins.

I would be very appreciative to learn what function these depressions had in the manufacture of Ptolemaic bronze coins.
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United States
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 Posted 10/13/2013  10:41 pm  Show Profile   Bookmark this reply Add chrsmat71 to your friends list Get a Link to this Reply
someone wiser in the ways of coins than I said recently that they may have been used to as a place for pinchers to grab the flan to flip it.



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Australia
13810 Posts
 Posted 10/14/2013  12:28 am  Show Profile   Bookmark this reply Add Sap to your friends list Get a Link to this Reply
There are two contending theories as to the cause of "centration dimples" found on certain ancient bronze coins (specifically, the bronzes of Ptolemaic Egypt and of certain Roman Provincial cities in the Danube region and Asia Minor).

1. The blank was screwed onto a lathe to allow the edge to be smoothed into a more-or-less round shape prior to striking. The faces may also have had some smoothing done at the same time. Evidence: dimpled coins do tend to be smoother and rounder than undimpled coins of similar size and age. Further, the faces of some severely dimpled, weakly struck coins bear clear signs of lathe turning-marks.

2. Pincer-tongs were used to hold the blank in the forge until it just started to get soft, at which point the coin would then be placed between the dies and then struck. If the furnace were too far away from the anvil and/or the slave carrying the blank was too slow, the metal got too cool for the blow to obliterate all traces of the hole left behind by the tongs. Evidence: on some double-dimpled coins the dimples are asymmetric, which would be possible with tongs but not a lathe. Further, experimental archaeology has shown that large bronze coin blanks would have needed to have somehow been pre-heated to softening point prior to striking since hand-striking a cold blank simply does not bring up the details we see on ancient bronzes.

It is entirely possible that both theories are true for different coin series and different time periods. Minting technologies and techniques were closely guarded trade secrets which were no doubt lost and re-invented several times over the 1000 year long period of "ancient" coinage.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis
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 Posted 10/15/2013  11:26 am  Show Profile   Check FVRIVS RVFVS's eBay Listings Bookmark this reply Add FVRIVS RVFVS to your friends list Get a Link to this Reply
I have long subscribed to the 'theory' that the standard explanations of coin manufacture in ancient times do not adequately take into account the large sized AE's which are best represented by the Ptolemaic issues and the Roman Imperial sestertius as produced from the mid first century until the mid third century. These were very much 'prestige' issues and were obviously much more complicated to produce than the tiny late issues or coins of silver and gold which are relatively easy to stamp.
For most small sized planchet production Moe Larry and Curly will be sufficient for the actual manufacture. One fellow is bringing in the raw materials and placing the blank another handles the die placement and the last (idiot) swings a sledge hammer. Good enough.
But for banging out high relief large ounce sized coins in orichalcum I simply don't believe it ! As circumstantial evidence I would point out that nothing similar was produced in the type of quality seen until the invention of the modern coin press. Even screw type presses are noticeably low relief and cannot hold a candle to a high relief issue of Antoninus Pius. Specifically the double portrait (Pius & Marcus) Sestertius I own which measures 1/8 inch of relief distributed over both sides.
The central 'dimple' seen on Balkan issues and the Ptolemaic bronzes likewise give me pause. I don't really like either explanation. Of the 4 Ptolemaic AE I own and the seven Balkan coins I have not one has the dimples lined up within several millimeters. The smaller ones have closer alignment but they are all but impossible to hold up using two ballpoint pens (which fit rather neatly)
The largest Ptolemy I own (67.63 grams) shows obvious signs of hammering around the edges. The next one down in size (35.67 grams) shows 'tool' marks similar to a steel cutting tool shaving a chamfered edge all the way around.The next down (31.68 grams) has a similar type edge but the tool markings look much more rasplike. Perhaps a combination of both was used. Lastly my little fellow (9.34 grams) which has a relatively 'normal' albeit angular edge which shows minimal signs of having been being cleaned up.

At first glance the little guy doesn't appear to have a 'dimple' but it does.




The big brother (35.67) has something very interesting though



The area of the dimple is shattered. Something 'violent' occurred which literally blew out the bronze leaving a jagged wound.

The other (31.68) has the best preserved dimple and also shows something very intriguing to me.



My father was a tool and die maker and operated a small manufacturing business for 35 years. 'We' produced a variety of hardware parts used in communications headsets and a variety of other products. Often when making something at a very fast rate (sometimes measured in thousands per hour) springs are used to expel a piece in order that the new material coming in does not result in two pieces getting formed and crushed together. For tighter spaces it is necessary to use a polished round headed pin with a spring adjustment below. If the spring gets broken or caught somehow, the smooth pin instead of expelling the object cleanly will instead leave an imprint or a 'dimple'.

Look closer ....




I see a hole made by a rounded pin mounted on the inside of a die with a raised donut like area around it caused by it being slightly too deep. Whether this pin was on a spring I can't say but I am almost certain it was present when the coin was stamped.
One of the consequences of the recycling of the old sestertii in the later Empire was the embrittlement of the orichalcum alloy. The evaporation of the zinc in the smelting process gradually resulted in fractures becoming the norm in late Imperial sestertii and eventually the metal was of the same appearance as bronze. It did result though in a change in the production of the blanks. Brittle alloy and the blanks being used suddenly become squared instead of round. Brass can be like hard bubblegum when trying to cut. Embrittled bronze is easy to chop into pieces. The standard theory is they used a chisel to chop up stips. Could be. But being clever fellows they might have built a continuous shear powered by a rotating ' CAM' and simply hand fed the strips into the 'machine'.

Of course these things would require something they did not know how to make. Steel.

Recycling bronze gives you an altered alloy that is hard and brittle. They could hardly have understood the metallurgy or why the zinc was disappearing. Recycling broken iron weapons and tools gives you something else though. The Romans did not know how to make steel. But they did have it in stock. If you remelt the iron enough times the carbon will slowly build up from exposure to the coal fire and eventually you will get steel. Hardly high grade tool steel but by pure accident you will eventually get some alloys that will have enough of the right trace metals to make some blades that they hardly could not have noticed were head and shoulders above the weapons carried by some new recruit ! These weapons might even have become famous and were surely handed down as family treasures.

The idea that a machine or machines were used to make coins is not considered probable by most people. The idea that the ancients had any clue about precision machines is rather silly idea isn't it ?

The Antikythera Mechanism



"The Antikythera mechanism (/ˌæntɨkɨˈθɪərə/ ant-i-ki-theer-ə or /ˌæntɨˈkɪθərə/ ant-i-kith-ə-rə) is an ancient analog computer designed to calculate astronomical positions. It was recovered in 1900- - "1901 from the Antikythera wreck, but its significance and complexity were not understood until a century later. Jacques Cousteau visited the wreck in 1978 but, although he found new dating evidence, he did not find any additional remains of the Antikythera mechanism. The construction has been dated to the early 1st century BC. Technological artifacts approaching its complexity and workmanship did not appear again until the 14th century AD, when mechanical astronomical clocks began to be built in Western Europe."
IN GOD WE TRVST ....... all others pay cash !

COGITO ERGO SPVD
I think ...... therefore I yam
Edited by FVRIVS RVFVS
10/15/2013 11:29 am
Pillar of the Community
United States
3229 Posts
 Posted 10/15/2013  10:34 pm  Show Profile   Bookmark this reply Add TJsCoins to your friends list Get a Link to this Reply
Cool FR!
Bedrock of the Community
Australia
18966 Posts
 Posted 10/16/2013  01:59 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
FVRIVS RVFIVS & Sap: I am indebted to your answers and reasonings. Interesting.
Ta!
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