Chemical Composition of Copper-Based Coins of the Roman

11 Chemical Composition of Copper-Based

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Coins of the Roman Republic, 217-31 B . C . Giles F. Carter and Hossein Razi Department of Chemistry, Eastern Michigan University, Ypsilanti, M I 48197

Twenty-two coins from the years 217 to 31 B.C. of the Roman Republic were analyzed by X-ray fluorescence for Fe, Co, Ni, Cu, Zn, As, Ag, Sn, Sb, and Pb. No evidence was found for widespread remelting of coins. The early coins are remarkable for their relatively high Co contents. Several coins have exceptionally high Pb, As, or Sb contents. Generally, the compositions of these Roman Republican coins are very different from those of Roman Imperial coins. Although few coins were analyzed, their compositions correlate reasonably well with time. Further analyses are required to determine whether composition varies with denomination and whether coins may be dated to within a few years by their chemical compositions. Microstructures of two Roman Republican coins containing lead are presented.

( j H E M I C A L A N A L Y S E S O F S E V E R A L H U N D R E D C O P P E R - B A S E D C O I N S of

the

R o m a n E m p i r e have c o n t r i b u t e d to the solutions of n u m i s m a t i c p r o b l e m s such as debasement a n d quality c o n t r o l (see refs. 1-6). F o r e x a m p l e , d e basement of the brass coinage of the R o m a n E m p i r e has b e e n s t u d i e d b y C a l e y a n d R i e d e r e r (5, 6), w h o f o u n d a progressive decrease i n z i n c contents over the course of m o r e than 100 years b e g i n n i n g w i t h the r e i g n of N e r o . C a r t e r has b e e n able to arrange four issues of A u g u s t a n quadrantes i n relative chronological o r d e r o n the basis of c h e m i c a l compositions (2). D e t a i l e d k n o w l e d g e of the c h e m i c a l compositions may b e u s e d to date an u n k n o w n issue (4). I n a d d i t i o n , i n f o r m a t i o n m a y b e o b t a i n e d c o n c e r n i n g ancient t e c h nology o n the basis of the k n o w l e d g e of c h e m i c a l compositions a n d m e t a l l u r g i c a l m i c r o s t r u c t u r e of ancient coins. 0065-2393/89/0220-0213$06.00/0 © 1989 A m e r i c a n C h e m i c a l S o c i e t y

Allen; Archaeological Chemistry IV Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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ARCHAEOLOGICAL CHEMISTRY


U n f o r t u n a t e l y , o n l y scattered, i n c o m p l e t e , a n d sometimes u n r e l i a b l e analyses have b e e n r e p o r t e d for copper-based coins of the R o m a n R e p u b l i c (7-10). M a n y R e p u b l i c a n copper-based coins w e r e large a n d rather ugly. T h e y o b v i o u s l y w e r e not m a d e of h i g h p u r i t y c o p p e r , b r o n z e , o r brass. W h e n A u g u s t u s , the first R o m a n e m p e r o r , began striking copper-based coins from relatively p u r e c o p p e r o r f r o m the n e w alloy, brass (ca. 23 B . C . ) , his coins m u s t have made a d e e p psychological i m p r e s s i o n o n the populace. T h e R o m a n s p r o b a b l y c o n s i d e r e d that such a vast i m p r o v e m e n t i n the c o p p e r based coinage i n d i c a t e d a b e t t e r form of government.

Experimental Procedure T w e n t y - t w o copper-based coins of the R o m a n R e p u b l i c w e r e a n a l y z e d for F e , C o , N i , C u , Z n , As, A g , S n , Sb, and P b by using X-ray fluorescence a c c o r d i n g to the procedures d e s c r i b e d b y C a r t e r a n d B o o t h (11). G e n e r a l l y , X - r a y fluorescence d e t e r m i n e s elements o n l y i n a t h i n surface layer, about 5 - 1 0 μπι d e e p , so i t was necessary to clean coins for analysis i n s u c h a w a y that the surface l a y e r was as representative of the e n t i r e c o i n as possible. F i r s t , the coins w e r e c l e a n e d b y electrolytic r e d u c t i o n i n a hot s o l u t i o n of s o d i u m carbonate. N e x t , the coins w e r e a b r a d e d i n an air stream c o n t a i n i n g finely d i v i d e d a l u m i n u m oxide p o w d e r to r e m o v e about 10 to 15 μπι of m e t a l . C a r t e r a n d B o o t h d e s c r i b e d the c l e a n i n g p r o c e d u r e i n d e t a i l as w e l l as the X - r a y fluorescence parameters (11). F l u o r e s c i n g X - r a y s from most elements i n a c o i n are almost c o m p l e t e l y absorbed b y 5 - 1 0 μπι of c o p p e r . I f the c o m p o s i t i o n of the surface l a y e r is significantly different from that of the i n t e r i o r , inaccurate results w i l l b e o b t a i n e d b y X - r a y fluorescence analysis. C a r t e r a n d K i m i a t e k (12) r e p o r t e d that concentration gradients apparently are u n c o m m o n i n c o p p e r a n d brass coins. H o w e v e r , l e a d e d bronzes often have concentration gradients because of segregation o f l e a d - r i c h or t i n - r i c h phases d u r i n g solidification. T h e l e a d rich phase is l i q u i d to a m u c h l o w e r t e m p e r a t u r e than copper. U p o n c o o l i n g of a l i q u i d c o p p e r - l e a d alloy, the lead can m o v e away from the surface of the m e t a l as i t freezes. H o w e v e r , i f the c o i n flan solidifies q u i c k l y , the gradient may b e m i n i m a l . A second p r o b l e m w i t h surface inhomogeneities i n metals is the d e p l e t i o n of a m o r e c h e m i c a l l y active phase i n contact w i t h a less c h e m i c a l l y active phase. W h e n two m e t a l l i c phases are i n electrical contact, the m o r e c h e m ically active phase of the alloy corrodes m u c h m o r e r a p i d l y than n o r m a l , e v e n w h e n it is exposed to e v e n a m i l d l y corrosive e n v i r o n m e n t . I f a c o i n has t w o phases exposed at the surface, s u c h as c o p p e r a n d l e a d , t h e n the m o r e active m e t a l , n a m e l y l e a d , w i l l corrode preferentially. H o w e v e r , cor rosion stops locally as soon as a g i v e n lead particle is c o n s u m e d . T h e c o p p e r matrix t h e n prevents f u r t h e r corrosion of l e a d because the c o p p e r phase m u s t first corrode before a d d i t i o n a l l e a d is exposed at the surface. H e n c e ,


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Coins of the Roman Republic, 217-31 B.C.

215


r e m o v a l o f a t h i n l a y e r o f m e t a l at the surface of a c o i n usually exposes m e t a l that is representative o f the c o m p o s i t i o n o f the e n t i r e c o i n (12). T h e p r i m a r y exception is l e a d e d b r o n z e , of w h i c h there are several coins i n this study. T h e analyses of l e a d e d bronzes b y X - r a y fluorescence are l i k e l y to be somewhat inaccurate. H o w e v e r , w e feel that useful i n f o r m a t i o n is still o b t a i n e d b y the X - r a y fluorescence analysis o f such coins. T h e l e a d a n d t i n c o n c e n trations, although not accurate, do p r o v i d e a fair i n d i c a t i o n o f the c o n c e n trations of these elements. F u r t h e r m o r e , k n o w l e d g e of the concentrations of m i n o r a n d trace elements i n l e a d e d bronzes is useful. Because surface roughness reduces the n u m b e r of fluorescing X - r a y s that leave a surface, the concentrations w e r e n o r m a l i z e d to 100%. E l e m e n t s such as oxygen a n d s i l i c o n w e r e not d e t e r m i n e d , b u t w e assume that these concentrations w e r e v e r y l o w (probably less than a total of 0.5%). N o r m a l ization to 1 0 0 % r e s u l t e d i n a slightly h i g h value for copper. N a t i o n a l B u r e a u of Standards ( N B S ) alloys w i t h certified compositions w e r e u s e d as standards along w i t h C e n t r e T e c h n i q u e des Industries de l a F o n d e r i e ( C T I F ) standards. T h e s e standards cover a fairly w i d e range of t i n and l e a d concentrations. W h e n no standards w e r e available that h a d c o m positions close to those of the coins, corrections for the effect o f l e a d a n d t i n contents w e r e calculated o n the basis o f the presence of these elements i n various standards.

Physical Measurements Table I lists the w e i g h t s , densities, m a x i m u m a n d m i n i m u m diameters, m a x i m u m thicknesses, a n d d i e orientations of the coins. T h e coins are i d e n tified b y C r a w f o r d n u m b e r (10). Because the coins have b e e n n o n d e s t r u c t i v e l y a n a l y z e d , t h e i r p h y s i c a l measurements w i l l identify the coins at any t i m e unless the coins are d e l i b e r a t e l y altered. Because R e p u b l i c a n coins w e r e made for such a l o n g t i m e , the d e n o m inations of coins c h a n g e d w i t h respect to w e i g h t and m e t a l content. M o s t denominations w e r e m a d e v e r y sporadically. A l t h o u g h asses w e r e m a d e for a l o n g t i m e , i n some instances there w e r e gaps i n p r o d u c t i o n o f m a n y years. T h e weights of asses decreased as a function of t i m e b y at least a factor of 2. T h e c h e m i c a l compositions also changed m a r k e d l y w i t h t i m e . P o o r q u a l i t y c o n t r o l m u s t have b e e n exercised because the coins v a r i e d i n w e i g h t a n d c h e m i c a l c o m p o s i t i o n e v e n w i t h i n a few years. D u r i n g the 200 years of c o i n p r o d u c t i o n i n the R o m a n R e p u b l i c , the variations i n the w e i g h t a n d c o m position of asses w e r e so great that i n some instances, one can scarcely b e confident that the d e n o m i n a t i o n has b e e n correctly assigned. T h e late brass asses are p r o b a b l y w o r t h twice the value of an as because of the p r e m i u m p l a c e d o n brass. C r a w f o r d has stated that these coins have a value of at least a d u p o n d i u s , a c o i n of the R o m a n E m p i r e w i t h a value of two asses (10).



? ? ? ? ? ?

217-215 217-215 211-210 ca. 211 189-180 169-158 149 148 134 108-107 90 90 88 86 45 32-31

Weight (g) 28.3140 6.2824 7.2719 10.3008 37.6548 19.7607 12.9326 13.0030* 3.3510 3.6734 3.3760 11.1772 11.7774 2.8260 12.0402 10.1068 19.2998 16.9688 20.3070 5.5235 10.7326 22.4730 0.520 0.520 0.318 0.288 0.565 0.406 0.377 0.304 0.226 0.265 0.200 0.341 0.319 0.254 0.309 0.401 0.415 0.384 0.357 0.260 0.396 0.439

Max. Thick. (cm) 3.03 2.19 2.22 2.64 3.42 2.97 2.57 3.09 1.99 1.64 2.14 2.91 2.89 1.56 2.79 2.42 2.94 3.50 3.20 2.08 2.49 3.00

Max. Diam. (cm) 2.91 1.98 2.10 2.46 3.12 2.58 2.33 2.84 1.82 1.59 1.97 2.58 2.61 1.47 2.69 2.23 2.81 2.66 3.09 2.02 2.40 2.84

Min. Diam. (cm)

-

?

4:00? 6:00

4:00?

?

5:00 12:00 1:30 1:00 10:30 2:30 12:30 12:00 8:00

3:00 11:00 6:00 10:00 3:00 3:00 7:00

Die Orientation 8.81 8.49 8.36 9.10 9.27 8.86 9.08 8.64 8.73 8.82 8.71 7.83 8.46 8.77 8.53 7.80 9.06 8.90 9.28 8.40 7.79 8.86

3

Density (glcm )

? ?

?

? ?

38/5 38/7 87/3 56/3 143/1 187/2 210/3 218/2a 244/3 308/4b 340/5a 342/7c 346/3 350B/3a 4776/la 1277 535/1

Coin Identification

b

The coin denominations are given by the letters: X, Sextans; M , Semuneia; U, Uncia; T, Triens; S, Semis; A, As; and Q, Quadrans. Reverse deeply abraded.

X-45 M-46 T-48 S-49 A-273 A-51 S-52 A-53 Q-80 U-89 S-91 A-93 A-92 Q-54 A-130 A-75 A-601 A-275 A-271 S-1601 T-1600 S-274

0

Coin

Date (B.C.)

Table I. Physical Measurements of Copper-Based Coins of the Roman Republic


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217

T h e densities of m a n y of the l e a d - c o n t a i n i n g coins are h i g h e r t h a n the density of c o p p e r (8.93 g / c m ) . H o w e v e r , b r o n z e ( C u - S n alloy) a n d brass ( C u - Z n alloy) b o t h have densities b e l o w that of p u r e copper, a n d i n d e e d , the m e a s u r e d densities of o u r coins reflect this fact. H o w e v e r , some of the cast coins have densities somewhat l o w e r than expected from t h e i r c h e m i c a l compositions. T h i s l o w density is p r o b a b l y caused b y i n t e r i o r porosity, w h i c h is rare i n R o m a n I m p e r i a l coins (the hot s t r i k i n g of these coins w o u l d t e n d to close i n t e r n a l pores). T h e density of c o i n T-1600 is 7.79 g / c m . T h i s v e r y l o w density is caused b y extensive i n t e r i o r corrosion of the c o i n . I n fact, the c o i n seems to have noticeably e x p a n d e d because of corrosion along grain boundaries into the i n t e r i o r of the c o i n . 3


3

T h e w e i g h t , d i a m e t e r , a n d thickness of an u n k n o w n c o i n m a y b e u s e d to h e l p date the c o i n . F u r t h e r m o r e , the c h e m i c a l c o m p o s i t i o n can i n d e p e n d e n t l y b e u s e d to a p p r o x i m a t e l y date coins of the R e p u b l i c . F i g u r e 1 shows two cast asses 0 a n u s o n the obverses a n d a p r o w of a ship o n the reverse of A - 5 1 a n d three prows o n the reverse of A-931). T h e s e coins are k n o w n to have b e e n cast i n a l o n g r o w because j u n c t i o n s b e t w e e n coins are v i s i b l e along the tops a n d bottoms of the c o i n obverses (see F i g u r e 1). A - 9 3 has m a n y s m a l l b u b b l e s on the surface; this b u b b l i n g is t y p i c a l of m a n y cast coins. T h e two brass coins, A - 1 3 0 (struck b y Julius Caesar) a n d A-75, are shown i n F i g u r e 2.

Chemical Compositions T h e c h e m i c a l compositions of 22 R e p u b l i c a n coins are g i v e n i n T a b l e I I . A l t h o u g h m a n y m o r e analyses are n e e d e d before a f u l l u n d e r s t a n d i n g of R e p u b l i c a n coinage is o b t a i n e d , some general observations are possible.

Figure 1. Cast coins A-51 (left) and A-93 (right). The length of the smallest division on the scale is 1.0 mm.



218


Figure 2. Brass coins A~75 (left) and A-130 (right). The length of the smallest division on the scale is 1.0 mm.

Table II. Chemical Compositions of Copper-Based Coins of the Roman Republic Coin" X-45 H-46 T-48 S-49 A-273 A-51 S-52 A-53 Q-90 U-89 S-91 A-93 A-92 Q-54 A-130 A-75 A-601 A-275 A-271 S-1601 T-1600 A-274

Date (B.C.) 217-215 217-215 211-210 After 211 189-180 169-158 149 148 134 108-107 90 90 88 86 45 32-31 ? ?

? ? ?

?

Fe 0.056 0.037 0.116 0.212 0.054 0.126 0.047 0.025 0.066 0.091 0.183 0.021 0.055 0.015 0.120 0.188 0.20 0.34 0.044 0.019 0.023 0.080

Co 0.117 0.064 0.181 0.175 0.154 0.122 0.032 0.018 Ν 0.013 0.021 Ν Ν Ν Ν Ν 0.077 0.056 0.080 0.027 0.084 0.062

m

0.041 0.071 0.053 0.048 0.056 0.040 0.055 0.060 0.036 0.072 0.67 0.106 0.074 0.25 0.007 0.006 0.095 0.040 0.055 0.026 0.022 0.040

Ζη Cu 95.3 0.02 91.0 0.02 87.5 0.04 82.9 0.02 86.1 0.01 83.6 0.01 81.5 0.01 72.1 Ν 99.1 0.03 93.3 0.03 85.0 0.01 96.8 0.01 95.9 0.01 98.4 Ν 78.8 20.8 82.9 15.7 87.5 0.01 86.8 0.09 81.2 0.02 88.3 0.01 69.1 0.01 83.8 0.02

As 0.17 0.37 0.28 0.27 0.18 0.48 2.3 2.5 0.01 0.07 0.32 Ν Ν Ν Ν 0.01 0.14 0.93 0.84 0.16 0.28 2.4

Sn Ac 0.032 3.75 0.033 8.2 0.041 9.0 0.037 5.4 0.028 6.1 0.052 3.9 0.18 3.0 0.10 1.9 0.33 0.13 0.081 6.1 0.21 7.3 0.105 2.7 0.28 1.8 0.15 0.52 0.066 0.081 0.091 1.07 0.068 7.7 0.094 3.2 0.078 3.3 0.034 11.5 0.013 2.7 0.29 1.9

Sb

Pb

0.023 0.065 0.106 0.060 0.037 0.124 2.4 2.5 0.15 0.075 1.4 0.18 0.53 0.29 Ν Ν 0.17 0.50 0.61 0.018 0.034 1.3

0.51 0.13 2.7 10.9 7.3 11.5 10.5 20.8 0.12 0.14 4.9 0.01 1.4 0.36 0.12 0.02 4.0 7.9 13.8 0.02 27.7 10.1

All element concentrations are given in weight percent. Ν means none detected (less than 0.01% for all elements). "The coin denominations are given by the letter: X, Sextans; M , Semuncia; U, Uncia; T, Triens; S, Semis; A, As; and Q, Quadrans. NOTE:


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219

I r o n concentrations are g i v e n as a function of t i m e i n F i g u r e 3. O n l y the compositions of coins of k n o w n or approximately k n o w n date are p r e sented i n F i g u r e s 3 - 1 0 . T h e i r o n concentrations are r e l a t i v e l y h i g h i n the two brass coins, A - 7 5 a n d A - 1 3 0 . Brass coins of the R o m a n E m p i r e u s u a l l y have h i g h e r i r o n contents than c o p p e r or b r o n z e coins, p r e s u m a b l y e i t h e r


because of the ores used or the procedures u s e d for p r o d u c i n g the alloys. M a n y of the i r o n concentrations are comparatively low. I r o n concentrations are h i g h l y variable a n d apparently do not correlate w i t h other e l e m e n t s , date of manufacture, or d e n o m i n a t i o n . A n c i e n t bronzes often contain rather l o w concentrations of i r o n , possibly because l o w e r temperatures w e r e u s e d to p r e p a r e c o i n flans (4). T h e amounts of cobalt f o u n d i n R o m a n R e p u b l i c a n coins are e x t r e m e l y i n t e r e s t i n g because they are so different f r o m those of R o m a n I m p e r i a l coins, w h i c h r a r e l y contain detectable cobalt. (The l o w e r detection l i m i t o f cobalt b y X - r a y fluorescence analysis is about 0.002% ). R e p u b l i c a n coins made before 135 B . C . a l l contain detectable cobalt, often i n r e l a t i v e l y h i g h c o n -

0.25

Ι

Ο

Semis

•

As

•

Quadrans

•

Other

0.20 h Ο

*

0.15h

0.05 h Ο

220

180

140 Date,

100

60

B.C.

Figure 3. Iron content of various coins.


20

220


Ο Semis •

As

• Quadrans


A Other

Ο Ο -j

ι

220

180

LB 140

ι

t

i

l

100

60

20

Date, B . C . Figure 4. Cobalt content of various coins. centrations (i.e. greater than 0.04%; see F i g u r e 4). C o i n s of the first c e n t u r y B . C . r a r e l y contain detectable cobalt. C o b a l t i n coins of the R o m a n R e p u b l i c came from a p a r t i c u l a r ore source. T h e absence of cobalt from most later coins indicates that t h e y w e r e made from a n e w ore source, rather t h a n f r o m r e m e l t e d coins or o t h e r metals. C o b a l t is a useful e l e m e n t for dating coins* F o r instance, c o i n A - 6 0 1 , w h i c h ostensibly was made i n 38 B . C . , contains cobalt. O n close i n s p e c t i o n , this c o i n was f o u n d to be an overstrike of an o l d e r coin. W e b e l i e v e that the c o i n was overstruck o n an as that was p r o b a b l y at least 100 years o l d at the time. Before 100 B . C . , the n i c k e l concentrations i n coins usually v a r i e d w i t h i n a fairly n a r r o w range from 0.03 to 0.07% (see F i g u r e 5). H o w e v e r , the two coins struck shortly after 100 B . C . are r e l a t i v e l y h i g h i n N i , a fact possibly i n d i c a t i n g the that the R o m a n m i n t used a different ore source for a short p e r i o d of t i m e . C a r t e r has r e p o r t e d two other periods of t i m e (ca. 2 3 - 1 5 B . C . a n d A . D . 2 2 - 3 0 ) , d u r i n g w h i c h the n i c k e l contents of I m p e r i a l coins are greater than 0 . 2 % (I). W i t h the two exceptions just m e n t i o n e d , the


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221

Ο

0.60

r

Ο

Semis

•

As

•

Quadrans

A

0.50

Other


0.40 L

._ ζ

0.30

0.20

0.10

0

1 220

• • • • ·· •

180

140

Date,

100

60

20

B.C.

Figure 5. Nickel content of various coins. n i c k e l contents o f the two late brass coins are q u i t e l o w , as are the n i c k e l contents o f early I m p e r i a l coins (23 B . C . to A . D . 66). T h e c o p p e r contents are not v e r y m e a n i n g f u l because c o p p e r was the matrix m e t a l . A n y standards of p r o d u c t i o n p r o b a b l y specified h o w m a n y parts b y w e i g h t o f an a l l o y i n g e l e m e n t (or ore) such as t i n or l e a d w o u l d b e a d d e d to copper. Z i n c was detected o n l y at v e r y l o w concentrations i n most R e p u b l i c a n coins. It was u s u a l l y present as a trace i m p u r i t y . H o w e v e r , two coins w e r e d e l i b e r a t e l y m a d e of brass; the earlier one was made b y Julius Caesar. T h e s e are the earliest k n o w n R o m a n coins m a d e of brass (13). Brass was a n e w a n d rather expensive alloy because it was necessary to make i t b y diffusion of z i n c vapor into copper. Z i n c was not p r e p a r e d i n m e t a l l i c form b y the R o m a n s or other ancient peoples because of its volatility. U n d o u b t e d l y , the s i m i l a r i t y of the colors of brass a n d g o l d m a d e brass unusually valuable to ancient people. C a r t e r has calculated the value a d d e d b y z i n c to the N e r o n i a n coins. T h e s e coins s h o w e d the most c o m p l e x use


222

•

2.4 r


Ο Semis

Ο

•

As

• Quadrans A Other


1.6h

-ι 220

ι 180

•• 140 Date, B . C .

••·· 100

β

t

60

ι 20

Figure 6. Arsenic content of various coins,

of various denominations o f copper-based coins made b y any R o m a n e m p e r o r (14). A r s e n i c o c c u r r e d i n r a t h e r h i g h concentrations (0.2% to about 0.4%; see F i g u r e 6) i n the coins struck before about 135 B . C . F r o m about 160 to 135 B . C . (an approximate date that marks a rather i m p o r t a n t change i n c o i n compositions i n general), the arsenic contents of four coins are greater t h a n 0 . 8 % (assuming that coins A - 2 7 5 a n d A - 2 7 1 , w h i c h have the p r o w of ships as f o u n d o n other R o m a n R e p u b l i c a n asses b u t w h i c h cannot be specifically i d e n t i f i e d , are dated w i t h i n this period). P r o b a b l y arsenic was d e l i b e r a t e l y a d d e d to these four coins (or perhaps a n ore exceptionally r i c h i n arsenic may have b e e n used). A l m o s t a l l o f the coins m a d e after 135 B . C . contain relatively l o w concentrations of arsenic. F r o m about 150 to 80 B . C . , most of the coins contained m u c h h i g h e r silver concentrations t h a n n o r m a l l y f o u n d i n copper-based R o m a n coins (see F i g u r e 7). T h e r e is no i n d i c a t i o n that s i l v e r was d e l i b e r a t e l y a d d e d to any


11.

CARTER & RAZI

223

Coins of the Roman Republic, 217-31 B.C. Ο Semis

0.36Γ

•

As

• Quadrans •

0.30 h

Other


Ο

220

180

I 140

100

60

20

Date, B . C . Figure 7. Silver content of various coins. of the coins that w e r e a n a l y z e d . A l l the s i l v e r levels are consistent w i t h the silver contents of c o p p e r ores. I f scrap m e t a l l i c objects w e r e occasionally m e l t e d to s u p p l y part o f the m e t a l for the coins, t h e n once i n a great w h i l e some s i l v e r - c o n t a i n i n g m e t a l m a y i n a d v e r t e n t l y have b e e n m e l t e d w i t h c o p p e r , a n d a somewhat h i g h e r t h a n n o r m a l c o n c e n t r a t i o n of s i l v e r r e s u l t e d . T i n was d e l i b e r a t e l y a d d e d to a l l the coins, w i t h t h r e e p r o b a b l e e x c e p tions (see F i g u r e 8). H e n c e , most of the coins are t r u e bronzes. T i n c o n t e n t g e n e r a l l y r a n g e d from about 3 % to 9%. T h e t i n d e t e r m i n a t i o n s b y X - r a y fluorescence

are of questionable accuracy because of i n h o m o g e n e i t i e s i n the

coins. O n e c o i n w i t h a l o w t i n c o n t e n t ( to w h i c h t i n was d e l i b e r a t e l y added) contains h i g h concentrations of a n t i m o n y a n d arsenic. T h e a n t i m o n y a n d arsenic w e r e e i t h e r i n a d v e r t e n t or i n t e n d e d substitutes for t i n . It is i m p o s sible to c o n c l u d e f r o m these data w h e t h e r t i n contents w e r e set at different levels for various d e n o m i n a t i o n s o f coins. H o w e v e r , b o t h quadrantes c o n t a i n no d e l i b e r a t e l y a d d e d t i n . A n t i m o n y contents are m o d e r a t e to v e r y h i g h c o m p a r e d w i t h the c o n tents of I m p e r i a l coins. F o u r coins from the m i d d l e of the second c e n t u r y


224


Ο Semis

9.Or

•

As

• Quadrans A Other


Ο

Ο

220

180

140

100

ι 60

t

20

Date, B . C . Figure 8. Tin content of various coins. B . C . contain v e r y h i g h a n t i m o n y concentrations, a n d two of these are s e m isses (only four semisses w e r e analyzed). T h e coins f r o m the earliest p e r i o d to about 160 B . C . contain moderate amounts of a n t i m o n y (see F i g u r e 9). M o s t o f the coins made f r o m a r o u n d 160 to 80 B . C . have r e l a t i v e l y h i g h a n t i m o n y contents; these same coins also w e r e relatively h i g h i n silver. T h e latest t w o coins have the v e r y l o w a n t i m o n y contents t y p i c a l of coins m i n t e d i n the early R o m a n E m p i r e . T h e coins m a d e before 135 B . C . are almost a l l l e a d e d bronzes ( F i g u r e 10). H o w e v e r , the two earliest coins, m a d e i n the late t h i r d c e n t u r y B . C . , have l o w l e a d contents. T h e l e a d contents increased r a p i d l y w i t h passing t i m e , u n t i l exceptionally h i g h l e a d contents w e r e f o u n d i n the coins o f three d e n o m i n a t i o n s : semisses, asses, a n d a t r i e n s , a l l of the m i d d l e of the second c e n t u r y B . C . T h e r e p o r t e d l e a d contents of some of these coins are p r o b a b l y l o w e r than the actual contents because of the segregation a n d surface d e p l e t i o n of lead. A p p r e c i a b l e amounts of l e a d w e r e not f r e q u e n t l y a d d e d to coins after r o u g h l y 100 B . C . A m a r k e d change i n the c o m p o s i t i o n of coins o c c u r r e d b o t h before 135 B . C . a n d after about 100 B . C . ( O n l y one


11.

CARTER & RAZI

Coins of the Roman Republic,

2.4r

217-31

B.C.

Ο

2.Oh

225

Ο

Semis

•

As

•

Quadrans

A

Other

1.6H


Ο CD

^

1.2|

0.8 I

0.4

•

220

180

100

140 Date,

60

t

20

B.C.

Figure 9. Antimony content of various coins. c o i n f r o m 135 to 100 B . C . was analyzed, a n d information f r o m this p e r i o d is unavailable).

Metallographic Examination of Two Coins C o i n A - 2 7 5 was g r o u n d , p o l i s h e d w i t h a l u m i n u m oxide, a n d t h e n etched b y continuous s w a b b i n g w i t h a solution of 20 m L of 1:1 a m m o n i a a n d 5 drops of h y d r o g e n peroxide. T h e cross section was several m i l l i m e t e r s from the edge of the c o i n . T w i n s are alternate light a n d dark e t c h e d crystals i n the same grain. T w i n s are crystals of closely related orientation separated b y a b o u n d a r y surface w h i c h is planar i n n o n d e f o r m e d twins. A s s h o w n i n F i g u r e 11, twins w e r e present i n almost every grain. T h e large gray particles are a l e a d - r i c h phase. Because the twins are not bent, the coin is not i n the asstruck c o n d i t i o n . T h e c o p p e r matrix of this c o i n is fairly soft: 74 to 102 V i c k e r s hardness n u m b e r ( V H N ) . A l t h o u g h there w e r e m a n y small l e a d particles present, a few large lead particles w e r e e v e n l y d i s t r i b u t e d t h r o u g h -


226


Ο Semis •

As

• Quadrans


A Other

Ο

Ο

220

J180

140

100

60

20

Date, B . C . Figure 10. Lead content of various coins.

out the c o i n . T h e hardness of the l e a d - r i c h phase was less than 17 V H N (extremely soft). T h e microhardnesses m e a s u r e d at the edge of the c o i n w e r e the same as i n t e r i o r microhardnesses. E i t h e r this c o i n was cast or it was annealed after s t r i k i n g . C o i n A - 2 7 1 (see F i g u r e 12) contained a few r e l a t i v e l y large lead particles, as w e l l as some s m a l l lead particles. T h e large lead particles t e n d e d to concentrate at the i n t e r i o r of the c o i n ; no large particles w e r e at the surface of the c o i n . T h e large l e a d particles contain small c o p p e r dendrites that p r e c i p i t a t e d as the l i q u i d l e a d cooled. F i g u r e 13 shows the l i g h t c o l o r e d c o p p e r d e n d r i t e s . T h e microhardness of the c o p p e r - r i c h phase ranged f r o m 105 to 130 V H N . T h e lead was e x t r e m e l y soft at 17 V H N . T h e lead i n this c o i n is u n d o u b t e d l y present i n a h i g h e r concentration than that r e p o r t e d b y X - r a y fluorescence. C o i n A - 2 7 1 apparently was cast a n d not subsequently struck, otherwise the large l e a d particles w o u l d have b e e n appreciably flat tened.



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CARTER & RAZI


Figure 11. Microstructure

227

of coin A-275. The length of the smallest division on the scale is 2.5 \Lm.

Figure 12. Microstructure of coin A-271 showing a large particle of lead. The length of the smallest division on the scale is 20 μπι.



228


Figure 13. Copper dendrites inside a large particle of lead in coin A-271. The length of the smallest division on the scale is 2.5 \im.

Comments on Individual Coins T h e brass as of Q . O p p i u s (A-75) shown i n F i g u r e 2, has not b e e n dated w i t h any certainty. It has b e e n assigned a date of 3 2 - 3 1 A . D . , b u t C r a w f o r d (10) is i n c l i n e d to ascribe this issue to about 88 B . C . T h e c h e m i c a l analyses support the later date. T h e v e r y l o w a n t i m o n y and the l o w n i c k e l content b o t h w o u l d place this c o i n i n the late R e p u b l i c , not i n 88 B . C . It is possible that the c o i n c o u l d have b e e n p r o d u c e d i n a m i n t far from R o m e , b u t the advanced technology necessary to p r o d u c e brass w o u l d make this u n l i k e l y . T h e as of A u g u s t u s a n d Julius Caesar (A-601) is an overstrike o n a m u c h o l d e r coin. T h e overstrike accounts for the presence of cobalt as w e l l as other anomalies i n the c o m p o s i t i o n of this c o i n (e.g., r e l a t i v e l y h i g h n i c k e l a n d a n t i m o n y contents). T h e dates of the coins, A - 2 7 1 , A - 2 7 4 , A - 2 7 5 , S-1601, a n d T-1600, are u n k n o w n . T h e f o l l o w i n g dates are estimated o n the basis of t h e i r c h e m i c a l compositions a n d weights: A - 2 7 1 (ca. 160 B . C . ) , A - 2 7 4 (ca. 150 B . C . ) , A 275 (ca. 160 B . C . ) , S-1601 (ca. 1 6 0 - 1 8 0 B . C . ) , T-1600 (ca. 1 8 0 - 2 0 0 B . C . ) .

Conclusions 1. N o e v i d e n c e supports the w i d e s p r e a d r e m e l t i n g o f coins. T h e later coins contain m u c h l o w e r concentrations of several e l e ments than earlier coins. C e r t a i n l y most o f these e l e m e n t s , especially cobalt, w o u l d have appeared i n r e l a t i v e l y h i g h c o n -


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CARTER & RAZI


229

centrations i n r e m e l t e d coins. H o w e v e r , coins that c o n t a i n e d l o w cobalt concentrations c o u l d have b e e n made f r o m a m i x ture of o l d coins that c o n t a i n e d cobalt a n d n e w m e t a l made from ore that c o n t a i n e d no cobalt.


2.

Chemical compositions correlate reasonably well with time. C o i n s may be dated approximately f r o m t h e i r compositions. T h e compositions of coins m a d e before about 1 3 5 - 1 0 0 B . C . are c o n s i d e r a b l y different from a l l later coins. C o i n s m a d e a r o u n d 80 B . C . are different w i t h respect to t h e i r contents of several elements w h e n c o m p a r e d w i t h compositions of coins from other t i m e s . T h e late R e p u b l i c a n coins also have u n i q u e compositions. F i v e coins w e r e approximately dated o n the basis of t h e i r c h e m i c a l compositions a n d weights.

3. Chemical compositions of Republican copper-based coins are markedly different from those of Imperial coins. I n the t i m e of A u g u s t u s , the c o i n compositions changed considerably f r o m those of e a r l i e r R e p u b l i c a n coins. T h e coins of A u g u s t u s that w e r e m i n t e d i n R o m e w e r e m u c h p u r e r ; they w e r e struck i n two materials: i n essentially p u r e c o p p e r a n d i n brass (15). 4. Early Republican coins are remarkable for their high cobalt contents and many for their exceptionally high lead, arsenic, or antimony contents. T h e cobalt contents are u n i q u e l y h i g h i n early R e p u b l i c a n coins c o m p a r e d w i t h all R o m a n coins made from about 135 B . C . to A . D . 400. S o m e late I m p e r i a l R o m a n coins contain h i g h amounts of l e a d , b u t not as h i g h as i n the early R e p u b l i c a n semisses a n d asses. 5. Additional analyses are required before one may reliably conclude that chemical composition correlates with d e n o m ination. T h e r e are indications that c o m p o s i t i o n correlates w i t h d e n o m i n a t i o n (e.g., the exceptionally h i g h l e a d contents of m i d - s e c o n d - c e n t u r y B . C . semisses a n d asses a n d the l o w l e a d contents of quadrantes). H o w e v e r , larger n u m b e r s o f coins m u s t b e c h e m i c a l l y a n a l y z e d to obtain a t h o r o u g h u n d e r s t a n d ing of the R o m a n R e p u b l i c a n copper-based coinage.

Denominations T h e as was the largest d e n o m i n a t i o n of copper-based coins of the R o m a n R e p u b l i c . T h e values of the other coins w e r e as follows: • two semis e q u a l one as • three triens e q u a l one as • four quadrans e q u a l one as

#

six sextans e q u a l one as

#

t w e l v e u n c i a e q u a l one as

Various denominations w e r e not c o n t i n u a l l y struck; there w e r e l o n g periods d u r i n g w h i c h no coins w e r e struck for each of the d e n o m i n a t i o n s .


230


Acknowledgment W e thank R o b e r t M e C o r k l e for the o p p o r t u n i t y to analyze his coins, S-1601 and T-1600.


References 1. Carter, G . F.; Buttrey, T. V. A m . Numismatic Soc. Mus. Notes 1977, 22, 49-65. 2. Carter, G . F. In Archaeological Chemistry II; Carter, G . F., E d . ; Advances in Chemistry Series No. 171; American Chemical Society: Washington, D.C., 1978; pp 347-377. 3. Carter, G . F. In Archaeological Chemistry III; Lambert, J. B., Ed.; Advances in Chemistry Series No. 205; American Chemical Society: Washington, D.C., 1984; pp 311-329. 4. Carter, G . F.; King, C. E . In Metallurgy in Numismatics I; Royal Numismatic Society: London, 1980; pp 157-167. 5. Caley, E . R. Orichalcum and Related Ancient Alloys; Numismatic Notes and Monographs No. 151; American Numismatic Society: New York, 1964. 6. Riederer, J. Jahrbuch Numismatik Geldgeschichte 1974, 24, 73-98. 7. Phillips, J . A . Quarterly J. Chem. Soc. of London 1852, 265. 8. Caley, E . R. In The Composition of Ancient Greek Bronze Coins; American Philosophical Society: Philadelphia, 1939. 9. Bahrfeldt, M. Numismatik Z. 1905, 9-56. 10. Crawford, M. In Roman Republican Coinage; Cambridge Univ. Press: C a m bridge, 1974, Vol. II, 573-577. 11. Carter, G . F.; Booth, M. M. In Problems of Medieval Coinage in the Iberian Area; Instituto Politecnico de Santarem: Santarem, Portugal, 1984, 49-69. 12. Carter, G . F.; Kimiatek, M. H. Archaeo-Physika 1979, 10, 82-96. 13. Burnett, A . M.; Craddock, P. T.; Preston, K. In Proceedings of the Int. Congress of Numismatics; Hackens, T.; Weiler, R., E d s . ; Louvain-la-Neuve, Luxemburg, 1982, 263-268. 14. Carter, G . F. Am. Numismatic Soc. Mus. Notes, 1988, 33 i n press. 15. Carter, G . F. In Science and Archaeology; M I T Press: Boston, 1971, 114-130. RECEIVED for review December 29, 1987. A C C E P T E D revised manuscript July 19, 1988.


Chemical Composition of Copper-Based Coins of the Roman

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