Minters strike again: an in-depth study of the French medieval minting techniques from an historical, archaeometric and experimental point of view ARLES Adrien1, TÉREYGEOL Florian2, GRATUZE Bernard1 1
Institut de Recherches sur les Archéomatériaux (IRAMAT), Centre Ernest-Babelon, CNRS, Université d’Orléans, France. - Contact:
[email protected] 2 Institut de Recherches sur les Archéomatériaux (IRAMAT), CNRS UMR 5060, LMC - LAPA, CEA , France - Contact:
[email protected]
The La Rochelle Royal Mint
Methodology
In the Nineties excavations in La Rochelle (France) have unearthed the vestiges of the second royal mint (XIVth – mid XVIIth century). It is a remarkable finding as this workshop is the only one that has been discovered in France up to now. The study of the numerous artefacts found (303 samples) allow the understanding of the whole coin making process: the hammer striking process1.
In order to propose the reconstitution of the coining process trough out the Middle Age in France, we set up a multidisciplinary approach: - The monetary sources (treatises, accounts...) reveal a theoretical “chaîne opératoire”. - Archaeometric studies: metrology, structural and elemental analysis. Archaeological experiments: creation of analogues that can be compared to the archaeological artefacts. It allows to produce defaults linked with distinct operation in a process. The reconstitution is also important to understand a technical operation.
Scissels
Blanching
5 La Rochelle
Squares Blanks
This operation is repeated several times during the process along with the beating on the edges of the blanks. Thanks to the beating, the blanks spread and evolve toward a rounder shape. They become thinner but larger. The study of the La Rochelle blanks revealing this trend, confirms the use of this process in the Royal Mint. 3,5 3
Monnayages d'argent Monnayages de billon Monnayages de bas billon Monnayages de cuivre
2
1,5 1
0,5 0
5 Silver Monnayages minting d'argent 10 Monnayages de billon Billion minting Monnayages bas billon Dark billiondeminting Monnayages de cuivre Copper minting
3,5 3
15
20
25
30
Longueur (mm)
Silver solid solution (Ag) Copper solid solution (Cu) Eutectic mixture (silver-rich)
2,5
Weight percentage of copper
Weight % silver: 100 Final colour:
2
1,5
71,9
15-10 8
1
Monetary alloy:
0,5
Silver
Billon
Dark billon
0
5
10
15
20
25
30
Length (mm)(mm) Longueur
La Rochelle
Alloying ■
The mechanism also explains the final color of the coins depending on the monetary alloys. We can have silver appearance with a relatively low silver content (10-15 w.%). On the contrary the 0% precious metal in the dark billon is too Copper diluted or defect in the copper solid solution, to give a dense enriched layer.
La Rochelle
Hammering ■ the strips
Casting ■ the strips
70 % Cu – 30 % Ag
2,5
Epaisseur (mm)
The monetary alloys are first casted in strips. They are next hammered to be thinned and only lengthen. The hammering stamp on the La Rochelle strips, quite perpendicular to the longest dimension, confirm this wish.
2 Beating out the blanks on the anvil (‘flatis’)
Thickness (mm) Epaisseur (mm)
1 Hammering the strips
Metallographic cross section of blank
Knowing the chemical mechanism of the blanching process leading to a superficial silver enrichment of the blanks3, we have now a better understanding of the archaeometric observations carried on the La Rochelle artefacts. On the cross section, we can notice different structures of silver enrichment. On one hand the more important silver density of the upper layer is inherited from the blanching process. On the other hand the density of the lower layer, similar in the core of the blank, is only the result of a copper depletion due to the corrosion in the soil.
La Rochelle
Strip
1
Beating out ■ the squares
■ Cutting the squares
■ Shearing the squares
Beating 2 out the blanks ■ on the anvil (‘Flatis’)
■ Beating out 3
■ Blanching 5 ■ Striking on a pile 4 of blanks (‘Boués’)
■ Striking 6
the edges of blanks held in pile (‘Rechaussés’)
3 Beating out the edges of blanks held in pile (‘Rechaussés’) 2 This process has two purposes that follow each other along the multiple repetitions of the operations during the minting. In the first steps, the aim is to round the squares to tend to the shape of the blanks (a, b). But in the final steps, the operation allows to standardize the metrology of the blanks (c).
≈ During the hammering, the blanks Défauts in contact withassociés the pliers are scratched by the tool. The same defect can be observed on both experimental and archaeological ≈ samples. Defects
Striking on a pile of blanks (‘Boués’)
4
6
It is the last mechanical step of the process. This operation is very important to produce blanks that are very flat. As the blanks are piled up, the pressure during the hammering is well distributed. It is also thanks to the defects resulting of this strike that the operation has been identified. In fact, if a blank is slightly moved out the pile during the striking, the profile surrounding of the blanks will be printed on its surface.
≈ Defects
La Rochelle
La Rochelle
Conclusions In this study, we have exposed the main operations used in the French hammer striking of silver and copper coins until the mid XVIIth century. It reveals their complexity, their purpose and the skills of the workers along the process. These results have been gathered thanks to a global interdisciplinary research with different complementary approaches. The experimental work takes an important part. The reproduced samples are easily studied, compared with the archaeological ones from a morphological and structural point of view. The experimental approach is also a pragmatic method allowing us to point out the complexity of a process and to understand its purpose.
Striking
Eventually the blanks are struck between two engraved dies. This operation is often illustrated by a one man job. In fact, this configuration allows to control precisely the position of the dies (parallelism of the surfaces) to produce well struck coins. It is also why the blanks need to be very flat.
4
Bibliography 1. Arles A., Téreygeol F., Études des structures et des objets liés à la fabrication de la monnaie, in Mille P., Téreygeol F., ed., L'atelier monétaire royal de La Rochelle, Fouilles de la place de Verdun, Presses universitaires de Rennes, 2011. 2. Schaffhausen Mint, stained glass, Berlin Münzkabinetts. 3. Arles A., Téreygeol F., Gratuze B., “Two silvering processes used in the French medieval minting”, Proc. Archaeometallurgy In Europe 2007, 17-21 june 2007, Aquileia, Italy. 4. Sante Barbara church, Kutná Hora, Czech Republic.
