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Lathe Machining of Bronze Coin Flans
 
Continued (p.4)

 The dimples in these Roman Provincial coins vary significantly, some dimples clearly showing a raised central bump which may perhaps explain why a flan would be cast with a raised bump in the center. Figure 7  illustrates such a dimple, on a bronze of Philip I struck in Mesembria, Thrace. Note that in this case also, there is an adjacent raised bump on the flan. The most reasonable interpretation of this central bump in the dimple is that the dimple was formed by the impression of a tool with a central cavity which left a bump on the coin. 


Fig. 7
Dimple containing  a central bump next to a raised flan bump 

In the coin shown in Figure 7, this bump and the bump cast into the flan are so similar that one suspects they are related in some way. A reasonable possibility is that the bump in the flan may have been intended to locate the tool which formed the dimple, and that when the dimpling tool was impressed into the flan, the operator (presumably a slave) was careless and did not properly locate the flan relative to the tool before making this impression. 

A bronze coin of Gordian III struck in Tomis, shown in Figure 8, indicates that the process which formed of the central dimple was sometimes omitted. Here we see a prominent central bump in the flan without evidence of any adjacent dimple.  It is of course possible that a dimple once existed on this flan but was filled during the striking process.  


Fig. 8
Central bump without a dimple 

This case of a central bump being present without a dimple is also found on a bronze coin of Gordian III struck at Odessos in Thrace, shown in Figure 9. Note that in this case there is no evidence of a dimple on either side of the coin. 


Fig. 9
Central bump without a dimple 

The edges of these Roman Provincial bronze coins tend to be irregular and are often cracked. The edges of some Provincial coins also exhibit clips which must have been caused by a void or other flan defect near the point where the runner entered the flan, which caused part of the flan to stay on the runner when the flan was being broken away from the casting tree. Figure 10 illustrates one example of such a flan edge clip, on a bronze coin of Philip II struck in Mesembria.  


Fig. 10
Edge clip from runner breakaway 

It seems quite clear from the many edge defects seen in these coins that the edges of their flans were not machined but were left as cast, perhaps after some filing to clean up the area where the runner was broken off. 

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