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Some simple observations on ancient coin flans

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Andrew McCabe:
Another key feature of coin flans is whether they are made in one-sided or two-sided moulds, and if in two-sided moulds, was the impression in one side or on both sides, and is the mould impression rounded or conical. The pictures below the message show a range of possibilities (adapated from RRC). These distinctions are particularly evident in thick coins, but in principle any coin could be looked at to see if it can be determined what is the type of mould.

fig.A shows a simple one sided mould. There may be sprues, or there may not - the "not" case implies a blob of metal was poured into the cavities, one flan at the time. The "sprues" case implies the cavities are all linked up. It's my belief that a lot of small denomination silver flans were made this way.

fig.B shows a two-sided mould, with a flat face on one side, and conical sides. This was more often used on struck bronze Republican coins of 218 to 210 BC, and from 110 BC to 95 BC. Because of the flat side, the other side of the mould is necessarily twice as deep. Because of that, sloped conical sides are often used to make sure the flan can be extraceted from the mould. This type of mould is dramatically shown in the picture below: the obverse is a good 6mm smaller in diameter than the reverse, with smaller devices, and the conical shape of the flan is very evident.

I've observed that these conical two-sided flans were only used in periods where teh coinage was in general of a very high quality, so it's clearly a more difficult way to make a coin flan.

fig.C shows a two-sided mould, conical sides.

fig.D shows a two-sided mould, rounded sides, which is the most usual type for Republican bronzes. In this case, the two sides are not perfectly aligned, and you can see an offset. This is particularly obvious in second century BC Republican asses. Here are two such offset flans, both incidentally from the same coin series, which is a key point: flan manufacture is often a key distinguisher.

In general I think insufficient attention has been made to flan characteristics; they are rarely recorded in catalogues, yet I think we might learn a lot about mint techniques and it may be of help in arranging coin issues. I've observed one coin series (RRC 106, staff and club bronzes from Luceria), where the As and Semis are the same diameter and were made using the same moulds. How? The As was made in a type C mould (two-sided, conical). The Semis used only one side of the same mould, i.e. type B, against a flat plate! On average, due to separatation between the moulds, the semisses of that series weigh about 60% of what an As weighs. Clearly this idea of producing very broad thin semisses with conical flans was a Bad Idea, because there's only one series it happens with. One observes and one learns. Someone should write these things down one day.

Studies of flans shows that good pictures are not always enough - I need to look at the coins from the sides to see how they were made, and thus to handle them in person.

Andrew McCabe:
I want to show another flan oddity, on the Victoriatus below.

The sprues are untypical, with a twisted shape on one side and a crack on the other side, and there's no evidence of any edge marks on the flan on this or any other coin of this type. Furthermore, on some coins of this type, a microscopically thin hair-line is visible on the surface of the coin, joining the two sprues, both on the obverse and the reverse. This particular coin is too strongly struck to show the hairline; but when visible, the hairline is the clue to the flan.

This flan was spherical, made by casting globes of metal (presumably in double-sided moulds) with thin sprues; once the sprues were removed, the flan was randomly placed on the die and struck. As it was a ball, the sprues were not necessarily at the edges but might be anywhere on the coin, obliterated by the strike. However the join-line between the moulds must always intersect the edges at exactly two points, 180 degrees from each other. So what looks like sprues are not sprues at all, but marks the interface between the two sides of the moulds, where they were not exactly aligned.. The hairline that I mentioned as visible on some coins is that interface between the moulds running across the coin. If this explanation is tough to follow, then imagine a type D flan but with hemisperical depressions, making a globule that is then struck in a random direction. Look at the diagram below: where the edge-line of the globe intersects the edge of the coin, you get a small crack or protrusion (not actually a sprue), and perhaps a visible line connecting the two protrusions/cracks across the coin face, the vestiges of the line on the globe where the moulds joined.

This needs you to think in 3 dimensions. So you may get a headache! NB the coin is exceptionally thick and high relief, which makes sense if we believe it was struck from a spherical flan.

Lloyd Taylor:
Fascinating stuff!

I'd never given much thought to the consequences of a spherical flan manufacture process and your explanation turned on a light bulb with respect to the fourth century BC sigloi of Byzantion. I have the example below which has what I always thought to be a ragged one sided casting sprue. A lot of these coins of Byzantion exhibit this in various forms and to varying degrees, but equally striking (pardon the pun) is the  massive variability in an irregular flan shape. I always had trouble explaining the latter. The flattening of a spherical flan during striking explains all the observed phenomena.

Thanks for the great explanation which "turned on the light bulb" for me.

Lloyd Taylor:

--- Quote from: Andrew McCabe on February 26, 2013, 08:48:15 am ---.....This needs you to think in 3 dimensions. So you may get a headache! NB the coin is exceptionally thick and high relief, which makes sense if we believe it was struck from a spherical flan.

--- End quote ---

The light bulb also now illuminates for this one... fourth century BC Neapolis where again we see the same relic "sprue" and with a similar thick fabric that bears with rounded soft edge/circumference that is consistent with the even squashing of a sphere between the dies (or possibly the result of some pre-strike processing and flattening via a nicely centered and evenly directed hammer blow?).

Lloyd Taylor:
Some silver coins, particularly those of Medieval origin typically show a fabric that is partially the result of post-strike adjustment, via clipping to bring them below the weight standard ( the mints of the time never issued overweight silver coinage - underweight was preferred by these nickel and dimers!).

Two examples are shown below for Trebizond (showing the edge nibbled away by cutting with shears) and Ragusa (where the whole circumference shows evidence of trimming by shears).

The tool marks left by the iron shears used to trim the coins can resemble edge filing, but this is not a sign of fakery, rather it is the result of a mint weight adjustment process!

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