Coins brass

Figure 1 shows two cast asses (Janus on the obverses and a prow of a ship on the reverse of A-51 and three prows on the reverse of A-931). These coins are known to have been cast in a long row because junctions between coins are visible along the tops and bottoms of the coin obverses (see Figure 1). A-93 has many small bubbles on the surface this bubbling is typical of many cast coins. The two brass coins, A-130 (struck by Julius Caesar) and A-75, are shown in Figure 2.

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

Iron concentrations are given as a function of time in Figure 3. Only the compositions of coins of known or approximately known date are presented in Figures 3-10. The iron concentrations are relatively high in the two brass coins, A-75 and A-130. Brass coins of the Roman Empire usually have higher iron contents than copper or bronze coins, presumably either because of the ores used or the procedures used for producing the alloys. Many of the iron concentrations are comparatively low. Iron concentrations are highly variable and apparently do not correlate with other elements, date of manufacture, or denomination. Ancient bronzes often contain rather low concentrations of iron, possibly because lower temperatures were used to prepare coin flans (4). 

Brass coins of Nero minted in Rome appear to have a significantly lower content of zinc than those minted in Lugdunum at the same time (4,5). 

SEVERAL HUNDRED COPPER-BASED ROMAN COINS have been analyzed by wet chemistry (J-5), x-ray fluorescence spectroscopy (6-11), and atomic absorption spectroscopy (12). Consequently, a general understanding of the compositions of copper-based Roman coins is developing. For instance, the debasement of orichalcum (Roman brass) coins by substituting tin and lead for zinc during the late first and second centuries is well known (1,12). 

Roman Brass Coins, Tho first brass c< in that was used at Romo was called... 

The electrical industry is one of the greatest users of copper. Iron s alloys -- brass and bronze --are very important all American coins are copper alloys and gun metals also contain copper. 

Homogeneous alloys of metals with atoms of similar radius are substitutional alloys. For example, in brass, zinc atoms readily replace copper atoms in the crystalline lattice, because they are nearly the same size (Fig. 16.41). However, the presence of the substituted atoms changes the lattice parameters and distorts the local electronic structure. This distortion lowers the electrical and thermal conductivity of the host metal, but it also increases hardness and strength. Coinage alloys are usually substitutional alloys. They are selected for durability—a coin must last for at least 3 years—and electrical resistance so that genuine coins can be identified by vending machines. 

These properties, coupled with its relatively low cost, make copper one of the most useful metals in modem society. About half of all copper produced is for electrical wiring, and the metal is also widely used for plumbing pipes. Copper is used to make several important alloys, the most important of which are bronze and brass. Both alloys contain copper mixed with lesser amounts of tin and zinc in various proportions. In bronze, the amount of tin exceeds that of zinc, whereas the opposite is tme for brass. The discovery of bronze sometime around 3000 bc launched the advance of civilization known today as the Bronze Age. Because bronze is harder and stronger than other metals known in antiquity, it became a mainstay of the civilizations of India and the Mediterranean, used for tools, cookware, weapons, coins, and objects of art. Today the principal use of bronze is for bearings, fittings, and machine parts. 

THE CHEMICAL STUDY OF EUROPEAN BRASS TOKENS AND COINS... 

Copper, being easy to mine and refine, has become a very versatile metal over the course of civilization. Early in human history, it was discovered that soft copper could be made harder and stronger when alloyed with other metals. Copper was and still is important to technology and the development of civilizations. Over the past several thousand years, brass has found multiple uses, such as in coins, cooking utensils, and many types of instruments and hardware that are resistant to corrosion. Even today, brass is used to make musical instruments and bathroom, kitchen, and marine hardware. The U.S. one-cent penny was originally made of copper, but today the penny is made of zinc with a coating of copper. Copper is also an alloy metal used as a substitute for some of the silver in several other U.S. coins. 

The Sung Dynasty (960 - 1280 A.D.) was one link in a chain of imperial dynasties throughout the history of China. At the time of the manufacture of the coins used in this study, established practice dictated that the coins be cast in clay molds, in a traditional manner that was already nearly one thousand years old. Thus, the coins analyzed in this study are all round, with a square hole in the center, have four characters on one side and none on the other, and are said to be of copper, bronze, or brass (/, 2). The characters on such coins are read from top... 

Our interest in this series of coins stems from earlier research in which coinage of emperors of the Ch ing Dynasty (also transliterated Qing ) were examined and found to be impure brass (5). We are interested in determining how far back such minting, and the required metallurgical knowledge, went. 

Modern brass and bronze alloys come in many different compositions, but 2 1 ratios of copper and zinc or tin respectively are used in a number of applications. Ancient and medieval alloys that are called brass and bronze are often mixtures of all three elements, with several other elements present as well. Observing a clean composition of copper and zinc or of copper and tin in any of the samples in this study would be a good indicator of a modem, counterfeit coin. None with such a composition were found. 

None of the coins can be considered to be brass. While a few of the many samples did have a small amount of zinc, most had such low concentrations that they were close to the lower detection limit of the instrument. 

The bronze compositions are decidedly different from the elemental make up of later series of Qing Dynasty cash from the 18 century, which are brass (3). Perhaps obviously, a significant change in coin metallurgy occurred between these two etas. It may be worth investigating when this change occurred, and determining what the reasons were for such. 

Older references to these coins simply indicate them to be copper, brass, or bronze (/, 2). The experience from our research and that of others indicates that ancient alloys are usually more complex than either a single element, or a simple alloyed mixture (3-18). 

The coins are leaded bronze. The almost complete absence of zinc indicates they are definitely not brass. 

The alloy of zinc with copper is termed brass, pinchbeck, Muntz metal, and tombac. English brass usually contains 70 per cent, of copper and 30 of zinc. It is made by melting the copper and adding the molten zinc. The addition of nickel (Cu 52 per cent., Zn 23 per cent., Ni 13 per cent.) yields German silver, of which spoons, forks, and coins are made. Electroplate has usually a basis of this alloy, and is covered with silver by depositing it from its double cyanide with potassium. Zinc coated over... 

The reason for it is not obvious since gold is not a very rare element on earth, and other metals, for example, platinum, rhodium, osmium, and rhenium, are less abundant and more expensive. Its yellow color cannot be the reason either, since other metals, such as copper, and its alloys as bronze or brass, have different colors from the bright silver of most of the metals. Probably, the reason resides in its noble character. In fact, gold does not tarnish with time, and coins and jewelry remain indefinitely unalterable even after long exposure to extremely aggressive conditions. 

Mankind has used copper throughoutrecorded history. People learned to refine it from copper ore near 5000 BC. It was used for pottery, tools, coins and jewelry. Because ofits softness, Cu was no t useful for weapons and tools until itwas hardened by alloying it with other metals brass is Cu and zinc bronze is Cu and tin. Modern alloys are copper-aluminum and copper-nickel. Copper is one of the best conductors of electricity, so that it is widely used commercially for wiring. Its resistance to tarnishing by oxidation makes it a popular but expensive roofing material. 

Applications.—Copper is employed in large quantities in the manufacture of electric conductors and apparatus, and for many other purposes. Its alloys are of the highest importance in the arts, examples being the so-called bronzing powders,1 brass, gun-metal, coins, and so on. 

The densities of many of the lead-containing coins are higher than the density of copper (8.93 g/cm3). However, bronze (Cu-Sn alloy) and brass (Cu-Zn alloy) both have densities below that of pure copper, and indeed, the measured densities of our coins reflect this fact. However, some of the cast coins have densities somewhat lower than expected from their chemical compositions. This low density is probably caused by interior porosity, which is rare in Roman Imperial coins (the hot striking of these coins would tend to close internal pores). The density of coin T-1600 is 7.79 g/cm3. This very low density is caused by extensive interior corrosion of the coin. In fact, the coin seems to have noticeably expanded because of corrosion along grain boundaries into the interior of the coin. 

Zinc was detected only at very low concentrations in most Republican coins. It was usually present as a trace impurity. However, two coins were deliberately made of brass the earlier one was made by Julius Caesar. These are the earliest known Roman coins made of brass (13). Brass was a new and rather expensive alloy because it was necessary to make it by diflusion of zinc vapor into copper. Zinc was not prepared in metallic form by the Romans or other ancient peoples because of its volatility. 

Undoubtedly, the similarity of the colors of brass and gold made brass unusually valuable to ancient people. Carter has calculated the value added by zinc to the Neronian coins. These coins showed the most complex use... 

The brass as of Q. Oppius (A-75) shown in Figure 2, has not been dated with any certainty. It has been assigned a date of 32-31 A.D., but Crawford (10) is inclined to ascribe this issue to about 88 B.C. The chemical analyses support the later date. The very low antimony and the low nickel content both would place this coin in the late Republic, not in 88 B.C. It is possible that the coin could have been produced in a mint far from Rome, but the advanced technology necessary to produce brass would make this unlikely. 

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