Just go with the flow (lines)

I'm not very geeky when it comes to the actual minting process and metallurgy of the coins I collect, but I'm probably like many others in that I get more interested when those aspects produce striking visual results. Flow lines are one of those things, and they can be quite dramatic in appearance, beautiful even. The Lucius Verus below is a recent addition to the collection, and on the obverse you can see long flow lines radiating outwards from the bust, over the legends and towards the edge of the coin.

Flow lines seem particularly common on coins from certain periods (Antonine denarii from my own obsveration), and more obvious on the obverse than the reverse. If you have a coin with strong or dramatic flow lines that make you like it more, please let us see it!


LUCIUS VERUS
AR Denarius
3.4g, 19mm
Rome mint, AD 166-167
RIC III 574
O: L VERVS AVG ARM – PARTH MAX, laureate head right.
R: TR P VII – IMP IIII COS III, Victory advancing left, holding up wreath in right hand and palm in left.

The writeup below on flow lines is by Barry Murphy, from an old list posting I dug up online.

"Flow lines develop in the die, not the flan. When a coin is struck the flan expands from the center towards the edges. Flow lines appear in spots where the devices meet the fields or anywhere where there is a change in depth of the die. As a flan is struck and the metal expands, there is friction and a change of speed in the flow of the metal wherever there is a change in the depth of the die. The most abrupt change occurs where the devices meet the fields, but there are other places such as around the ears and eyes. This friction is what causes the flow line to appear in the die. At first they are microscopic, but with successive strike they grow. There is much less friction across the fields so you are much less likely to get flow lines in the fields, although, as a die is used more and more, the flow lines extending from the devices can extend across the fields. The most likely places for flow lines to develop are around the bust and at the tops of the letters, extending toward the rims, as you go from device to field.

"Where and when flow lines develop are a function of several factors. 1) The depth of the engraving. 2) How close the engraving is to the edge of the die. 3) The hardness of the die and the eveness of that hardess across the die's surface. 4) Whether the flan is struck hot or cold 5) How hard the dies are routinely struck. All these factors effect the speed the metal flows and in which directions it flows the fastest. The flow lines will develop quickest and deepest where the metal flows the fastest and where the dies are the softest.

"Even today, modern dies develop flow lines. It is these microscopic lines in the die that give a coin cartwheel luster. Modern dies though are repolished occasionally so the flow lines tend to be erased repeatedly. Ancient dies were not polished as frequently, if at all with most dies, and the flow lines would continue to grow as the die was used. Two coins struck from the same dies in relative proximity to each other should exhibit the same flow lines."

Here's an enlarged picture of the fields in front of the bust of my coin, with the lines showing up more clearly.

 

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Very interesting article! I didn't realize the flow lines developed on the die rather than on the coin but of course that makes perfect sense .

There is still much I don't understand about the metallurgy and mechanics of this. Why aren't flow lines seen more often on bronze coins? Bronze is harder, so at first though it seems more likely to "etch" the die as the metal moves but that doesn't seem to be the case. I've seen flow lines on highly debased antoniniani but not on sestertii or Greek bronzes. Or have I just not noticed them? Perhaps the patinas and other surface changes due to aging obscure small die surface features?

Looking through my coins I have very few with prominent flow lines. This Roman Republic denarius has some near the devices, nicely highlighted by iridescent toning:


Roman Republic, L. Julius L. f. Caesar
103 BC
AR denarius, 17mm, 3.9 gm
Obv: Helmeted head of Mars left; CAESAR; ・J above
Rev: Venus Genetrix in chariot left, drawn by two Cupids; lyre to left; ・J above
Ref: Crawford 320/1.
Jencek E-auction 26, lot 58, 14 October 2014. Ex CNG XXXI lot 699, September 1994; ex RBW Collection

AncientJoe has some aurei with spectacular but subtle flow lines radiating out from the coins' centers in a pleasingly uniform way.

 

Interesting and informative.

ANTONIUS PIUS
AR Denarius
OBVERSE: ANTONINVS AVG PIVS P P IMP II, laureate head right
REVERSE: TR POT XIX COS IIII, Annona standing left with corn ears & modius set on prow
Struck at Rome 155/6AD
3.1g, 17mm
RIC 249, C 983

 

I've wondered the same about bronzes. Those are some really lovely golden flow lines on that denarius... I remain very jealous. I'm always looking out for one (there was a nice one in yesterday's Roma), but inevitably the conclusion is "not as nice as TIF's".

 

They do seem particularly common on A-Pi's denarii.

 

Impressive flow lines Z!

This is probably my best example which shows them.


Vespasian
AR Denarius
Rome mint, 72-73 AD
RIC 356 (C3), BMC 64, RSC 45
Obv: IMP CAES VESP AVG P M COS IIII; Head of Vespasian, laureate, r.
Rev: AVGVR (above) TRI POT (below); Priestly implements

 

Nice! I really like how they flow from the devices on the reverse.

 

Gorgeous OP-winner, Z-Bro (very cool)

oh, I have a pretty sweet example of these flow-line thingies ...

=> Jazz-Hands!!

Arcadius Siliqua

 

Nice! Stare long enough at that reverse and you'll feel like how Arcadius looks.

 

Fascinating subject !!

I haven't noticed any with such obvious flow-lines, but I probably have one or two somewhere.

 

Antoninus Pius Denarius (as Caesar)
Obv:- IMP T AEL CAES ANTONINVS, Bare head right
Rev:- TRIB POT COS, Concordia,standing left, holding patera and cornucopiae.
Minted in Rome. February 25th to July 10th A.D. 138
Reference(s) – Cohen 1061. RIC II (Hadrian), p. 294 450 (C). BMC 1010, Strack 408.

 

Thank you for the article! And the flow lines are an interesting aspect to your coins...I really like them.

 

I would not let that guy near my kids !!!!

 

Two of my better flow-ers, a Phraates II drachm and a Mithradates II tetradrachm:

 

Great coin and very well written information on metal displacement Zumbly,thanks!

 

Nice piece Bing!

 

Those are two very dramatic examples alright. Thanks for sharing them!

 

very interesting about how flow lines come about Z, i didn't know that!

a great new coin! a nice LV was one of the coins i recently ordered that never made it to my house. and as much as i like flow lines, a don't really have one that shows them strongly.

 

Chalukya of Kalyana
Jayasimha II Jagadekhamalla,(r. AD 1015-1042)
AV Pagoda 18 mm x 3.79 grams
Obverse: 2 x Sri, Temple/ spearhead with central rosette. - Kannad Script -Jakadeva
Reverse: Uniface - Countermarked elephant right. Uncertain symbol.
Ref:Mitch, Karnataka Andhra 273 var