The Roman Empire
Domitia, with Domitian

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An ancient coin’s value depends on multiple factors, such as the extent of physical and chemical preservation. The most sought-after grade is “mint” state, i.e., virtually as struck at the mint. Less valuable are coins with circulation wear and/or chemical deterioration evident on their surfaces. Although considered detriments, such properties define the coin’s history, and often provide artistic appeal. Consider this very modestly valued bronze coin, struck late first century AD in the Koinon of Thessaly. Depicted on one side is a laureate Roman Emperor Domitian, while the other bears the draped bust of Roman Empress Domitia Longina (~53 AD - ~130 AD). Over the course of nineteen centuries, the coin’s surfaces have amassed circulation wear and chemical alteration. The resulting patina, particularly the complementary hues of green and red, lends an aesthetic appeal that is best appreciated firsthand.

Such patina is the result of specific, complex chemical reactions that, in turn, depend on environmental conditions and the coin’s chemical composition. This ancient bronze coin, like all “ordinary” matter within our universe, is comprised of atoms, differentiated by their atomic number into the chemical elements. A highly useful approach to understanding the chemical elements is to arrange them in rows with increasing atomic number left to right and columns with increasing number of electron shells from top to bottom. Each column within the resulting Periodic Table of the Elements represents a Group whose species tend to share similar chemistry. A notable example is Group 11, also known as the coinage metals, whose species are relatively chemically inert, electronically conductive, and corrosion resistant. Group 11 includes Cu (copper), Ag (silver), and Au (gold), all of which occur in nature and, not surprisingly, represent the first elements ever discovered.

The first metal coins, dating from 7th century BC Asia Minor, were struck from electrum, a naturally occurring alloy of gold and silver. Around the same time, techniques were developed to refine gold by exposure to low-oxygen and high temperature (~ 800 C) in the presence of sodium chloride. This process results in formation of silver chloride, facilitating the extraction of pure gold. Techniques were also developed to smelt silver chloride with lead over 1000 C in the presence of oxygen, resulting in formation of lead oxides, and the opportunity to isolate pure silver. In ancient times, such approaches allowed for production of gold and silver coins of unprecedentedly high purity. Coins were also produced from copper, more specifically copper alloyed with tin (and sometimes other compounds), referred to as bronze. This process, requiring temperatures of nearly 1100 C, originated thousands of years ago, delineating our Bronze Age.

Around the time ancient Lydians first fashioned electrum into coinage, the Romans, limited by their own locally sourced materials, used heavy, relatively unrefined bronze weights as currency. Over time, Rome’s territories expanded, as did access to precious metals and methods for their refinement. By about 3rd century BC, the Romans were striking coins made of not only highly refined copper, but also relatively pure silver and gold.

Among the Group 11 elements, gold is least reactive, thus most corrosion-resistant. Fortunately for collectors, it is not uncommon for ancient gold coins to still glitter, suggesting their ability to retain - audacious to imagine, original - luster. More reactive than gold is silver, still sufficiently corrosion-resistant that ancient argentum surfaces exist with lustrous, if not original, surfaces. While dry silver is stable, moisture promotes reactions with various other elements, particularly oxygen and sulfur. Chemical analyses of buried silver indicate that, depending on factors such as soil pH and composition, other chemicals reactions can occur. These processes can create dramatic surfaces on silver coins ranging from thick black crusts to iridescent rainbow toning. Compared to silver and gold, copper and its alloys are much more reactive. Copper and its alloys readily react with oxygen and sulfur, as well as many other chemical species. Because of their relative reactivity, ancient bronze coins typically exhibit some degree of patina. Such processes provide quite an interesting, multicolored palette: Cu₂(CO₃)(OH)₂ (malachite; green), Cu₂O (cuprite; red to yellow), CuO (tenoite; grey to brown), Cu₃(CO₃)₂(OH)₂ (azurite; dark blue), and Cu₂S (calcocite; metallic grey), just to name a few.

On this particular ancient bronze coin, the portraits of Augustus Domitian and Augusta Domitia, once lustrous bronze, now lie beneath a thick, dark, verdigris. In an irresistible parallel, the imperial couple’s repute also tarnished, thanks to the efforts of a highly literary, disapproving Senate. While many commoners and soldiers favored Domitian, his micromanaging, despotic style angered most Roman aristocrats, not to mention severely limited their authority. Not surprisingly, ancient historical records are highly critical of the last Flavian Emperor and those associated with him.

That’s not to say imperium critics didn’t have a wealth of juicy inspiration. Domitia’s affair with Domitian began as an adulterous one. At the time, she was still married to her first husband, from whom she subsequently obtained a divorce. In 71 AD, Domitia and Domitian exchanged wedding vows, although they both - reportedly - failed to uphold them. In any case, their relationship lasted a quarter century, after the first decade of which they served as Rome’s Emperor and Empress. The relationship lacked neither controversy nor discontinuity; in 83 AD, Domitia was briefly exiled amid rumors of her adulterous affair with Paris, a popular Roman pantominus. Domitia’s fall from grace did not last very long; she was soon recalled, probably to quell rumors that the Emperor was having a love affair with his niece, Julia Titi. Regardless of her true fidelity, Domitia’s marriage ended in 96 AD upon Domitian’s murder. Of course, some ancient sources implicate the Empress, which is plausible, but unlikely. Modern evaluation favors Domitia’s rehabilitation; she upheld Domitian’s memory up until her own death, sometime around 130 AD.

The true historical details reside somewhere beneath Domitia and her husband's tarnished legacy.

Coin Details: ROMAN PROVINCIAL, Koinon of Thessaly, Domitian and Domitia, AD 81-96, Æ Diassarion (19mm, 6.17 g, 12h), NGC Grade: Ch VF, Strike 5/5, Surface: 3/5, Obverse: Laureate head of Domitian right, star to right, ΔΟΜΙΤΙΑΝΟΝ ΚΑΙCΑΡΑ ΘΕCCΑΛΟΙ, Reverse: draped bust of Domitia right, ΔΟΜΙΤΙΑΝ CEBΑCTHN, References: Burrer Em. 2, – (A21/R45 [unlisted die combination]); BCD Thessaly I –; BCD Thessaly II 947; RPC II 284.