Constantine the Great

Metallurgy
of Constantinian "Bronzes"

    The bronze coinage of the Constantinian period from A.D. 307-348 should actually be thought of as a true silver denomination since these coins had carefully measured amounts of silver and quite often, a surface enrichment of silver.1 At the very least, these coins should be called argentiferous bronze coins! The percentage of silver during this period fluctuated from 1-5% silver, and varied from mint to mint. Fractional coinage always had less silver, and the commemorative fractions issued by Constantine in 317 had almost no silver. These coins had only trace amounts of silver-- 0.3% or less. The argentiferous alloys were comprised of mainly copper (Cu), lead (Pb), tin (Sn) and silver (Ag). Other impurities might include iron (Fe), nickel (Ni), cobalt (Co), zinc (Zn), gold (Au), arsenic (As), antimony (Sb), and Indium (In).2From A.D. 307-317, the amount of silver was circa 2-5%, and generally eastern mints had higher percentages of silver than the western mints, until Constantine became sole ruler of the Empire. From A.D. 318-320, there was circa 4% silver in the coinage. From A.D. 321-330, the silver content was circa 2%. After A.D. 330, the silver content was circa 1%, which was maintained until A.D. 341, when the silver dropped to less than 0.5%. Coins with only a trace amount of silver can no longer be thought of as argentiferous.3

   Many argentiferous coins of this period exhibit silvering on their surface. Through experimentation, some possible methods of surface enrichment of silver have been theorized.4 For flans with more than 5% silver, cold hammering followed by annealing resulted in lead and silver being forced to the surface. A dilute acid bath would give the flan a silvery surface. For flans that contained less than 5% silver, a bath in molten silver chloride displaced silver and deposited it on the surface, which gave the flan a silvery wash. Hot working and blanching prior to hot striking also enriched the surface silver content. There are other ways a coin could have a silvery surface. Corrosion may also promote a silvery surface on a coin. Lead corrodes very easily, and as it is displaced, silver can be deposited on the surface. Various  methods in the cleaning process can also give a coin a silvery appearance, such as heating a coin or even washing a coin. Lead can  be removed by prolonged washing, leaving more silver on the surface.5A recent study of the same coins analyzed by Cope showed that the silvering often contained mercury. Experiments were performed with a silver-mercury amalgalm and various heating cycles. Copper sheets were coated with silver-mercury pastes and heated. The alloy that best withstood the 600 degree temperatures had 62% mercury and 38% silver.6
 
 

 Analysis of the Composition of Alloys7


Date
Ruler
ObvLeg
Bust
Reverse
Mint
MM
RIC
WT
Ag
Pb
Sn
Cu
Zn
Ni
Fe
Sb
Au
Co
As
In
307-9
Constantine
IMP C CONSTANTINVS P F AVG
B
GENIO POP ROM
Lug
PLG
253
6.66
1.41
310-12
Constantine
CONSTANTINVS P F AVG
C
COMITI AVGG NN
Lon
*//PLN
153
4.45
1.51
9.56
3.39
85.12
0.01
0.02
0.03
 - 
 - 
0.04
310-13
Constantine
CONSTANTINVS P F AVG
B
SOLI INVICTO COMITI
Trier
T/F//PTR
873
4.89
1.38
6.05
4.87
87.18
0.02
0.04
0.06
0.02
310-13
Constantine
CONSTANTINVS P F AVG
C
SOLI INVICTO COMITI
Trier
T/F//PTR
874
4.42
1.74
4.88
5.27
87.46
0.02
0.04
0.03
0.05
310-13
Constantine
IMP CONSTANTINVS AVG
H11 left
VICTORIAELAETAE 
PRINC PERP
Trier
PTR
208a
2.01
24.28
313-17
Constantine
CONSTANTINVS AVG
B4
SOLI INVICTO COMITI
Lon
T/F//PLN
94
3.54
1.65
-
4.10
74.80
0.20
-
-
0.09
-
0.01
0.06
0.59
313-17
Constantine
IMP  CONSTANTINVS P F AVG
B5
SOLI INVICTO COMITI
Lug
T/F//PLG
17
2.91
1.47
7.58
4.84
86.02
0.02
0.03
-
-
-
0.03
-
-
313-17
Constantine
IMP CONSTANTINVS AVG
B5
SOLI INVICTO COMITI
Arles
S/F//PARL
60
3.05
0.98
12.47
6.43
79.91
0.02
0.07
0.06
0.12
-
0.02
0.04
-
313-17
Constantine
IMP  CONSTANTINVS P F AVG
B4
SOLI INVICTO COMITI
Arles
T*F
QARL
80
3.40
1.12
10.03
4.96
83.58
0.01
0.04
0.06
-
-
0.04
-
-
313-17
Constantine
IMP  CONSTANTINVS P F AVG
B4
SOLI INVICTO COMITI
Rome
R/F
R*P
19
2.44
1.25
6.66
5.74
86.08
-
0.02
0.04
-
-
0.05
-
-
313-17
Constantine
IMP  CONSTANTINVS P F AVG
B4
SOLI INVICTO COMITI
Rome
C/S
RT
40
3.97
0.83
13.05
5.05
80.30
0.02
0.08
0.09
-
-
0.05
-
-
313-17
Constantine
IMP C CONSTANTINVS P F AVG
C
SOLI INVICTO COMITI
Ostia
MOSTT
91
3.34
1.17
11.69
3.99
82.87
0.01
0.05
0.13
0.09
-
0.03
0.08
-
313-17
Constantine
IMP  CONSTANTINVS P F AVG
B5
SOLI INVICTO COMITI
Tic
*//ST
16
3.46
1.42
7.20
4.75
86.80
0.01
0.03
313-17 
Licinius
 IMP  LICINIVS P F AVG
 B1
IOVI CONSERVATORI
AVGG NN
Sis 
 gamma//
SIS
 4
 2.45
 1.65
 3.74
3.32
91.11
0.01
0.02 
0.03 
0.02
-
-
313-17
Licinius
IMP  LICINIVS
P F AVG
B1
IOVI CONSERVATORI
Sis
gamma//
SIS
17
2.69
1.30
3.82
2.93
91.54
0.01
0.04
0.05
-
-
0.01
-
-
313-17
Licinius
IMP C VAL LICIN
LICINIVS PF AVG
B1
IOVI CONSERVATORI
Nic
NB//
SMN
15
2.36
1.31
3.06
2.02
93.07
0.02
0.04
0.03
-
-
0.05
-
-
313-17
Constantine
IMP C FL VAL
CONSTANTINVS PF AVG
B1
IOVI CONSERVATORI
AVGG
Ant
A//
ANT
7
3.54
3.21
-
2.00
91.30
0.40
-
-
0.11
-
-
0.14
1.03
 318-20
 Constantine
IMP  CONSTANTINVS P F AVG 
H11
left
 VICTORIAELAETAE 
PRINC PERP
 Lon
 PLN
 158 
 2.97
3.70
2.95
3.58 
89.33
0.01 
0.02 
0.02 
0.01 
 318-20
 Constantine
IMP CONSTANTINVS
MAX AVG
D6 
 VICTORIAELAETAE 
PRINC PERP
 Trier
 *//STR
 213
 2.21
 4.80
 -
-
 318-20
 Crispus
DN CRISPO
NOB CAES
 B5
 VICTORIAELAETAE 
PRINC PERP
 Lug
2 capts. 
 75
 1.93
4.18 
 
4.40
88.10
0.50 
 0.11
0.07 
 0.84
318-20 
 Constantine
 IMPCONSTANTINVS
MAX AVG
 D6
 VICTORIAELAETAE 
PRINC PERP
 Arles
 SARL
 190
2.79 
3.74 
2.16
3.97
89.65
0.01 
0.08 
0.09 
0.03 
318-20 
 Crispus
 FL IVL CRISPVS
NOB C
C3 
 VICTORIAELAETAE 
PRINC PERP
 Tic
C//
ST
 93
3.17 
3.43
 
3.00
0.10 
0.10 
0.87 
318-20 
 Constantine
 IMP  CONSTANTINVS AVG 
H12
left 
 VICTORIAELAETAE 
PRINC PERP
 Sis
gammaSIS 
61 
3.00 
3.35 
 320-1
 Crispus
 CRISPVS
NOBIL C
 D2
 VIRTVS
EXERCIT
 Lon
 PLON
 188
 3.44
2.65 
3.21 
0.10 
0.06 
0.70 
 320-1
 Crispus
CRISPVS
NOB CAES
 D2
 VIRTVS
EXERCIT
 Trier
 STR
270 
2.08 
2.21 
3.07 
2.63
91.75
0.02 
0.04 
0.03 
 320-1
 Licinius
IMP LICINIVS
AVG
 B1
VOT XX 
 Arles
SARL 
 190
2.38 
1.39 
4.63 
4.51 
88.81
0.02 
0.08 
0.07 
0.02 
320-1 
 Crispus
 CRISPVS
NOB CAES
 G8 left
 VIRTVS
EXERCIT
 Tic
PT 
117 
3.39
3.28
4.32
3.94 
88.04
0.02 
0.02 
0.02 
0.04 
 320-1
Constantine 
 CONSTANTINVS
AVG
 B1
VOT
XX
Rome 
RT 
237 
2.40 
1.85
4.73
4.64
88.54
0.01 
0.03 
0.04 
0.01 
 320-1
 Constantine
 CONSTANTINVS
AVG
 B1
VOT
XX
Aq 
AQP 
65 
3.22 
1.94 
5.21
4.05 
88.67
0.03 
0.03 
0.05 
0.04 
 320-1
Licinius 
 IMP LICINIVS
AVG
 B1
VOT
XX
Sis 
BSIS* 
160 
2.78 
2.11 
4.81 
4.13 
88.74
0.02 
0.06 
0.06 
0.03 
-
 320-1
Constantine 
 CONSTANTINVS
AVG
 B5
 VICTORIA
AVGG
 Thess
.TS.delta
59 
3.36 
3.36
3.53
2.90 
91.47
0.01 
0.06 
0.03 
0.02 
321-4
Constantine II
CONSTANTINVS
IVN N C
D2 
left
BEAT
TRANQLITAS
Lon
PLON
287
2.32
1.80
5.36
4.55
88.08
0.02
0.03
0.06
-
-
0.07
-
-
321-4
Constantine
CONSTANTINVS
AG
B1
SARMATIA
DEVICTA
Lon
PLON
crescent
290
2.37
1.67
4.71
4.65
88.76
0.02
0.03
0.04
-
-
0.06
-
-
321-4
Constantine
CONSTANTINVS
AVG
D2
BEATA
TRANQVILLITAS
Trier
STR
341
3.43
1.93
7.78
2.43
88.17
-
0.04
0.04
-
-
0.03
-
-
321-4
Constantine
CONSTANTINVS
AVG
B5
BEATA
TRANQVILLITAS
Lug
C/R//
PLG
155
3.35
1.67
-
-
-
-
-
-
-
-
-
-
-
 321-4
Constantine 
CONSTANTINVS
AVG
B1 
VOT
XX
Thess 
TSAVI 
123
3.58 
2.25
2.47 
2.92 
91.52 
0.06 
0.09 
0.10 
0.05 
 321-4
 Licinius
 IMP C VAL LICIN
LICINIVS P F AVG
C3 
 IOVI
CONSERVATORI
Her 
XXIM//
SMHA
 52
2.04 
0.12 
4.52
0.78
92.80
0.01 
0.36 
0.86 
0.01 
 321-4
 Licinius
  IMP C VAL LICIN
LICINIVS P F AVG
 C3
 IOVI
CONSERVATORI
 Cyz
 XXIM//
SMKA
 15
3.40 
0.13 
6.09 
0.96
91.64
0.22 
0.47 
0.03 
 321-4
 Licinius
  IMP C VAL LICIN
LICINIVS P F AVG
 C3
 IOVI
CONSERVATORI
 Ale
 XXIM//
SMALB
 28
3.30 
2.23
0.65 
95.31
0.31 
1.12 
0.03 
 325-9
 Constantine
 CONSTANTINVS
AVG
 B1
 PROVIDENTIAE
AVGG
 Lon
PLON
 293
2.49 
1.70
4.85
4.16 
88.80
0.01 
0.02 
0.07 
0.03 
 325-9
 Constantine
 CONSTANTINVS
AVG
 B1
 PROVIDENTIAE
AVGG
 Trier
 PTRE
 504
2.14 
1.41 
6.61 
4.58
86.64
0.08 
0.02 
0.16 
0.06 
 325-9
 Constantius
II
 FL IVL
CONSTANTIVS
NOB C
 B4
left
 VIRTVS
CAESS
 Arles
 T/F//
PCONST
 338
1.85 
1.66 
5.24 
4.52
88.29
0.02 
0.04 
0.06 
0.06 
325-9
Helena
FL HELENA
AVGVSTA
E10
SECVRITAS
REIPVBLICAE
Her
SMHdelta
79
2.56
2.31
2.64
2.77
91.79
0.03
0.02
0.04
-
-
0.03
-
-
325-9
Constantine
CONSTANTINVS
MAX AVG
E2
LIBERTAS
PVBLICA
Cons
B//
CONS
25
3.12
3.28
-
-
-
-
-
-
-
-
-
-
-
325-9
Constantine
CONSTANTINVS
MAX AVG
E8
CONSTANTINIANA
DAFNE
Cons
A//
CONS
35
-
2.42
-
-
-
-
-
-
-
-
-
-
-
325-9
Constantine
CONSTANTINVS
AVG
B1
PROVIDENTIAE
AVGG
Cyz
.SMKgamma.
44
3.13
1.45
8.66
4.56
86.09
0.02
0.02
0.07
-
-
0.03
-
-
325-9
Constantine
CONSTANTINVS
AVG
E3
PROVIDENTIAE
AVGG
Cyz
SMKB
58
2.41
1.31
4.05
4.36
89.61
0.01
0.10
0.05
-
-
0.08
-
-
325-9
Helena
FL HELENA
 AVGVSTA
E10
SECVRITAS
REIPVBLICAE
Ant
SMANTZ
67
2.45
2.39
2.35
2.29
92.53
0.01
0.04
0.02
-
-
0.01
-
-
330-5
-
VRBS
ROMA
D3
left
wolf & twin
Trier
TRP
522
2.14
0.96
9.15
2.41
86.93
-
0.05
0.64
-
-
0.10
-
-
330-5
-
CONSTANTINOPOLIS
N1
left
victory on prow
Trier
TR.P
543
-
1.21
-
-
-
-
-
-
-
-
-
-
-
330-5
-
CONSTANTINOPOLIS
N1
left
victory on prow
Lug
.PLG
246
-
1.1
-
-
-
-
-
-
-
-
-
-
-
330-5
-
CONSTANTINOPOLIS
N1
left
victory on prow
Aqu
*//
AQS
129
-
0.96
-
-
-
-
-
-
-
-
-
-
-
330-5
-
CONSTANTINOPOLIS
N1
left
victory on prow
Nic
SMNA
196
-
0.96
-
-
-
-
-
-
-
-
-
-
-
330-5
-
CONSTANTINOPOLIS
N1
left
victory on prow
Ant
SMANA
92
-
1.4
-
-
-
-
-
-
-
-
-
-
-
330-5
-
VRBS
ROMA
D3
left
wolf & twin
Rome
-
315
-
0.86
2.85
0.34
94.99
0.01
0.11
0.20
-
-
0.31
-
-
330-5
Constantine
CONSTANTINVS
MAX AVG
E8
GLORIA EXERCITVS
two standards
Her
.SMHA
116
2.56
1.11
5.03
1.31
88.96
-
0.11
0.02
0.01
-
-
0.01
-
330-5
Constantine
CONSTANTINVS
MAX AVG
E8
GLORIA EXERCITVS
two standards
Cons
CONSH
59
2.44
1.17
3.29
1.98
93.24
0.03
0.20
0.02
-
-
0.14
-
-
330-5
Constantine
CONSTANTINVS
MAX AVG
E8
GLORIA EXERCITVS
two standards
Ant
SMANB
86
2.58
1.06
-
2.80
89.10
0.40
-
-
0.10
-
0.03
0.18
2.01
335-7
Constantine
II
CONSTANTINVS
IVN NOB C
B5
GLORIA EXERCITVS
one standard
Ale
SMALgamma
66
1.61
2.09
3.08
3.85
91.95
0.07
0.11
0.03
-
-
0.01
-
-

 
 
 



Suggested reading

Barrandon, J. N.,  and C. Brenot, “Analyse de monnaies de bronze (318- 340) par activation neutronique à l’aide d’une source isotopique de Californium 252.” Collection de l'Ecole française de Rome 37 (1978) : 123- 144.

Clay, Teresa. “Metallurgy and Metallography in Numismatics.” Numismatica e Antichità Classiche 17 (1988) : 341- 352.

Cope, L. H. “The Argentiferous Bronze Alloys of the Large Tetrarchic Folles of A.D. 294-307.” The Numismatic Chronicle 8 (1968) : 115-149.

________. “Die-Module Measurements and the Sequence of Constantine’s Reformed Folles Issues of Spring A.D. 310 and Early A.D. 313.” Schweizer Münzblätter 20 (1970) : 46-61.

Cope, L. H. and H. N. Billingham. “The Composition of 35 Roman Bronze Coins of the Period A.D. 284- 363.” Historical Metallurgy 1 (1967) : 1- 6.

Cope, L. H., C. E. King, J. P. Northover, and T. Clay. Metal Analyses of Roman Coins Minted Under the Empire. British Museum Occasional Paper 120, 1997.

King, C. E. “The Alloy Content of Folles and Imitations from the Woodeaton Hoard.” PACT: Journal of the European Study Group on Physical, 1 (1977) : 86-100.

Ravetz, A. “Neutron Activation Analysis of Silver in Some Late Roman Copper Coins.” Archaeometry 6 (1963): 46- 55.

Vlachou, C., J. G. McDonnell, and R. C. Janaway. “Experimental Investigation of Silvering in Late Roman Coinage.” Materials Research Society Symposia Proceedings 712 (2002) : 461- 470.


1  L. H. Cope and H. N. Billingham.  “The Composition of 35 Roman Bronze Coins of the Period A.D. 284- 363.”  Historical Metallurgy 1 (1967) : 1.

2 King, C. E.  “The Alloy Content of Folles and Imitations from the Woodeaton Hoard.” PACT 1 (1977) : 86-100. The metal Indium is occasionally found in alloys of fourth century coins. It is similar to aluminum and its most common isotope is very slightly radioactive.

3 Cope, L. H., C. E. King, J. P. Northover, and T. Clay. Metal Analyses of Roman Coins Minted Under the Empire. British Museum Occasional Paper 120 (1997) : 8.

4  L. H. Cope,  "Surface-Silvered Ancient Coins," Methods of Chemical and Metallurgical Investigation of Ancient Coinage (1972) : 275.

5Teresa Clay, “Metallurgy and Metallography in Numismatics.” Numismatica e Antichità Classiche 17 (1988) : 341- 352.

6  Vlachou, C., J. G. McDonnell, and R. C. Janaway. “Experimental Investigation of Silvering in Late Roman Coinage.” Materials Research Society Symposia Proceedings 712 (2002) : 461- 470.

7Most of this data is from Cope, L. H., C. E. King, J. P. Northover, and T. Clay. Metal Analyses of Roman Coins Minted Under the Empire, but some is from J. N. Barrandon and C. Brenot, “Analyse de monnaies de bronze (318- 340) par activation neutronique à l’aide d’une source isotopique de Californium 252.”  Sometimes the silver content is the only data recorded, as it was  the most important metal in the alloy.  The silver content directly  affected the value of the coin.
 
 

last modified on 21 Nov 2007

Constantine the Great

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