1 7 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 2 variant, even rarer still, with the accent similar to that of the letter (Ñ). The 1851 coin from the study is quite worn due to the passage of time, but when looking at the letter Q, it is seen that the tilde crosses toward the inside of the letter[3] (Fig. 7). For the 1851 coin, the 2% alcoholic ferric chloride solution (FeCl3) was also used as the etching reagent, which shows a structure with a well-formed recrystallized grain matrix with straight twin lines, and very little porosity (Fig 8). There is no evidence of a second phase. X-ray fluorescence analysis of both coins confirms that only minor, trace-type alloy components are involved, with copper being the main component. Chemical composition and metallographic evidence indicate that the alloy is of a single phase and aligns with the aforementioned decree of January 9, 1851, which said coins were to be made of refined copper without mixing any other metal. Table 2 lists hardness values for both coins. MINTING PROCESS According to the manufacturing method used at that time, metal was melted in crucibles in a coal furnace, and poured into prepared rails to form solid ingots. Ingots that did not meet the required thickness were passed between two rollers that pressed the metal strip, stretching it to the desired thickness. When the rail hardened it was necessary to anneal it to relaminate it. If the rail was too long, it was cut into smaller pieces. After the rails were a thickness equal to the blanks, they were anneal- ed to make them more workable. To protect against oxidation from an- nealing, the rails were put in ovens in sealed boxes. Automated machines were used to drill the rail and obtain the blanks. These machines were manually fed, and the operator had to move the metal strip forward to the rhythm of the machine. The cut blanks then went through the press, creating a pre-listel, a rim or raised border, which, among other things, helped protect the engraved pattern. The press was formed phase. Some intracrystalline cracks have also occurred due to copper corrosion. METALLOGRAPHIC OBSERVATIONS OF THE 1851 CENT COIN Figure 5 shows an example of the one cent 1851 Chilean coin as listed in the Standard Catalog of World Coins. Similar to the 1853 coin, the obverse side says “REPUBLICA DE CHILE” with the five-pointed star in relief, and year of minting 1851 between two smaller stars. The reverse side says “ECONOMIA ES RIQUEZA,” the denomination in words is surrounded by laurels united with a double loop. There are variants regarding the shape of the letter Q in the word RIQUEZA (Fig. 6). The first type has the Q tilde outside of the letter (most common) and in the second type the tilde crosses the letter (rare). There is another (FeCl3). The 1853 coin shows a grain structure typical of hot working and annealed with some visible twin grains, variable grain size, and some porosity seen as dark holes due to corrosion (Fig. 4) There is no evidence of second TABLE 2 — COIN VICKERS MICROHARDNESS 1853 half-cent coin 1851 one-cent coin 1º 146 HV 138.7 HB 137 HV 130.15 HB 2º 132 HV 125.4 HB 109 HV 103.55 HB 3º 121 HV 115.0 HB 101 HV 95.95 HB AVERAGE 133 HV 126.36 HB 116 HV 109.88 HB Fig. 8 — Micrograph of the 1851 historical copper coin. Corrosion at the grain edge and detail of slight porosity. Reagent: Alcoholic solution of 2% ferric chloride (FeCl3). Magnification: 400x (a, b) and 100x (c). Fig. 6 — Three images of 1851 one-cent coins for the morphological comparison of the letter Q. Fig. 7 — Historical coin macroscopy of 1851 one-cent coin. (a) (b) (c)
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