About the Coins

Manufacturing Methods    (Info)

 

Metallurgy

 

The alloys used to produce flans for gold coins are remarkable (104). All are three-way alloys, the predominant metals being gold, silver and copper (152). However, the ratio of the three was intentionally varied over time to gradually and imperceptibly debase the metal.

Around 125 B.C., the Large Flan and Defaced Die types had a ratio of about 75 percent gold, 22 percent silver and 3 percent copper. The tribes then gradually replaced gold with silver, and by the time of the Abstract Design type, around 100 B.C., the ratio had dropped to less than 70 percent gold and over 25 percent silver, with copper constant. Forty years later, the Gallic War type was struck with less than 60 percent gold and something over 30 percent silver, copper now averaging around 10 percent. The sophistication of this debasement lies in the fact the gradual change in alloy would have been imperceptible – the colour of the metal would appear constant during the lifetime of a single generation.

After the Gallic War, the British tribes evidently had insufficient bullion and were forced to replace gold not only with silver, but also with copper. The Atrebatic Abstract and Whaddon Chase types were struck fairly close to the nominal alloy of the Gallic War type, but the succeeding inscribed types are quite different. The inscribed coins generally run 45 to 50 percent gold, 10 to 20 percent silver and 30 to 40 percent copper (105). At this point, the British staters take on their characteristic reddish tinge. The colour of the metal is not, however, a guide to its origin – red gold is not necessarily native to Britain, nor is yellower gold necessarily Continental. The tribes were carefully and intentionally controlling their alloys to attain economic goals. The switch from yellow to red gold marks an intentional debasement of the coinage.

 

Weight

 

While the tribes were debasing their alloys, they simultaneously reduced the standard weights. The Large Flan and Defaced Die type staters of 125 B.C. were struck to a standard of about 7.80 grammes. The staters were then dropped in stages of an almost imperceptible five percent over the next seventy-five years. Around 100 B.C., the Abstract Design type weighed 7.25 grammes, by 75 BC. it had dropped to 6.45. The Gallic War types, starting around 6.35 grammes, weighed only 5.80 at the end of the Gallic coinage. The British staters continued to drop, ultimately stabilizing at 5.40 grammes around 10 B.C.

The concerted decline in weight and gold content was orchestrated carefully and deliberately (106). The changes in the types, the minor die varieties within types and the field-objects are probably indicators the moneyers used to identify intrinsic value. Knowing these privy marks, a moneyer could identify the weight and gold content of a coin by sight. Celtic staters are seldom found with the chop marks often seen on Roman denarii. The reason is clear – the moneyers and other knowledgeable individuals must have been able to evaluate the coins by eye.

The exact sequence of this gradual debasement was only elucidated by means of Electron Microprobe Spectroscopy in the late 1980s. The corresponding die studies remain to be correlated to it, but this may be nearing completion in John Sills most recent work. However, the trends are sufficiently identified to predict the outcome – the coins were debased in a systematic way and the coins probably were marked for identification.

 

Die Production

 

Celtic dies exist in both iron and bronze. Few exist today, but the iron type is rarer than the bronze. This may be due, however, to the difference in survival of the two metals. Little is known of the manufacturing techniques, but the dies were certainly hand-cut using gravers, punches and perhaps the bow-drill. It is gradually being proven that the die-cutters used specialized punches containing a finished image. Whether hubbing was practiced, however, remains only a speculation. Almost without exception, the obverse dies were concave and the reverse ones convex. The curvature facilitated positioning the flan on the lower die and holding it in place for striking.

The alloys employed in the dies varied with the knowledge of the moneyers. Those used for the Whaddon Chase staters, for example, must have been punched in a soft metal. The field around punch marks is violently heaved from the force of the blow – an effect not seen, for example on South Ferriby staters. The softness of the Whaddon Chase dies caused them to break up rapidly and signs of die damage are common in this series. The South Ferriby reverses, on the other hand, seldom show the same extent of damage and evidently wore better. Celtic dies were often used well beyond their useful life, to the extent the image is often completely obliterated. The use of irretrievably damaged dies occurs more often on silver coins than on bronze or gold.

The earliest coins are struck from dies considerably larger than the flans, and no one coin contains the entire image. However, after the Gallic War, the sizes of the dies and flans were more closely matched, and most of the image was now captured. Possibly this was a direct result of the switch to inscribed coins – the ruler's name, at the edge of the die was often struck off the flan on the early inscribed types. Naturally, the ruler would be expected to protest, and the moneyers would have responded by reducing the size of the dies.

 

Striking

 

The flans, probably heated, were hand struck between the dies. Tongs have been found on at least one mint site, evidently used to handle hot flans (107). Despite heating, the gold coins normally have striking cracks at the edge. The bronze and silver coins tend not to have cracks to the same degree. Double-struck coins are not as common for the Celtic series as they are, for example, the mediaeval. For the most part, a single blow of the hammer was sufficient to strike up the design, despite the fact Celtic dies were normally cut in high relief. Brockages, extremely rare, are known (108), usually for the commoner issues where the moneyers would have been rushed and would not have noticed the error. The hammer-men seldom paid much attention to centering the flans on the dies and off-centre strikes are more common than perfectly centred ones. Centering was improved after the change to smaller dies, probably because an off-centre strike would then result in a blank area being recorded on a portion of the flan or again because a ruler's name would be omitted.

 

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