Archaeometallurgical Analysis of Electrum Coins

Electrum alloy, one of the earliest alloys worked by humans, formed naturally where gold and silver deposits occurred together. Artificially produced electrum is an alloy of gold (Au) and silver (Ag) and may also contain small amounts of copper (Cu), platinum (Pt), and iron (Fe) such as metals. The hue of electrum alloy varies depending on the ratio of gold to silver within it. It can contain 20–80 percent gold and 20–50 percent silver. When richer in gold it appears bright yellow, and when richer in silver it may appear pale yellow or grayish; it has a malleable and workable structure similar to gold. Its density also varies with the gold content but generally ranges between 10 and 15 g/cm³. Additionally, due to its gold content, it is highly resistant to corrosion.

_{Electrum Ore (}Source₎

Electrum was the preferred alloy for the production of the first coins in antiquity, for several important reasons. Primarily, as a naturally occurring alloy, it could be worked without the need for separation, offering an economic and practical solution. It was harder than pure gold, which is soft and easily worn, yet more durable and corrosion-resistant than silver. These properties enabled it to provide long durable money production opportunity.

The economic value of electrum was also high because it contained both gold and silver. This situation provided trading civilizations with a portable and valuable currency. Furthermore, the gold and silver ratios in electrum coins could be controlled to standardize their value. This served as an effective method to facilitate trade while deterring counterfeiting. Electrum, a symbol of wealth and prestige, represented the power of the Lydian Kingdom and other civilizations. The Lydian Kingdom introduced the first electrum coins in the 7th century BCE, establishing standardization in trade. The direct use of electrum as coinage facilitated commerce and generated an revolution in the economy.

_{Electrum Coins​ ()}

In Lydia, particularly in the alluvial deposits of the Pactolus River (Sart Çayı), natural electrum was used as a raw material for coin production. The gold-to-silver ratio in natural electrum varied depending on its source. To obtain a standardized alloy, electrum was first refined and then mixed in specific proportions to achieve desired properties.

The prepared standard electrum alloy was initially cast in broad bean form into small ingots, which were later hammered into thin metal sheets. These sheets were typically stamped with symbols such as lion or bull heads or king silhouettes reflecting the power and prestige of the Lydian Kingdom. The stamping process was not only crucial for determining the coin’s value but also for establishing its authenticity guarantee.

_{Electrum coin stamping (}Source₎

After stamping, the coins were carefully cooled and cleaned. These final steps prepared the electrum coins for circulation in trade. The processing of electrum into coinage introduced standardization to the economy of the period, facilitating trade and enhancing Lydia’s economic power.

_{XRF device ()}

XRF: A non-destructive technique that identifies elemental composition by analyzing characteristic X-rays emitted from the surface. In electrum coins, it rapidly determines the proportions of gold, silver, and copper and detects corrosion products. In one study, a PW4025 energy-dispersive spectrometer (bulk analysis) and an Olympus VANTA C portable XRF device (micro-area analysis) were used, with micro-area analyses conducted at four distinct points.

_{XRD device (}Source₎

XRD: A method used to examine the crystalline structure of materials and corrosion products. In electrum coins, it identifies the alloy structure and corrosion compounds such as chlorargyrite and cuprite. Its advantage lies in detailed analysis of crystal structure, though interpretation of results requires expertise.

Optical Microscopy: Used to examine surface morphology and corrosion products. In electrum coins, it visually assesses the distribution of corrosion products and the state of preservation. It offers Fast and ease of use but provides no chemical composition data. It must be supported by other analytical methods to be effective.

_{Optical microscope ()}

Neutron Radiography: A non-destructive technique used to examine the internal structure of metal coins. Neutrons penetrate deeply into metals, providing detailed information about internal building. As neutron beams pass through the coin, their distribution varies according to the material’s density. These distribution data are used to construct a 3D model of the coin, enabling detection of details such as pores, cracks, and coating layers.

_{Neutron radiography device. ()}

_{XRF analysis results (}Source₎

XRF Analysis Results from a Sample Study: Sample A contains 59 percent gold (Au), 31 percent copper (Cu), and 7 percent silver (Ag). This analysis confirms the surface is electrum. Sample B is notable for containing 57 percent silver (Ag), 24 percent copper (Cu), and 15 percent zinc (Zn). This composition indicates the object was manufactured with a brass base on and silver plating. Sample C contains 77 percent silver (Ag) with minor amounts of copper and zinc. Corrosion products such as chlorine and sulfur compounds were detected in surface analyses. Sample D has a composition of 74 percent silver (Ag) and 2.8 percent copper (Cu). The composition and dense corrosion traces on the surface of this sample provide significant insights into the preservation conditions of alloys used in antiquity.

_{XRD analysis results (}Source₎

XRD Analysis Results from a Sample Study: Sample A revealed silver-copper alloy (Ag-Cu) and gold (Au) phases on the surface. No corrosion products were detected, indicating excellent surface condition. Sample B identified alpha-brass (Cu-Zn alloy). Despite minor corrosion traces, the surface remains well preserved. Sample C contains chlorargyrite (AgCl) as silver corrosion products, cuprite (Cu2O) and tenorite (CuO) as copper corrosion products, and additionally paratacamite (Cu2(OH)3Cl). Sample D is dominated by acanthite (Ag2S) as silver sulfide corrosion, along with chlorargyrite and copper corrosion products (cuprite, tenorite). The distribution of corrosion products indicates the object was strongly affected by environmental conditions.

_{Optical microscopy images (}Source₎

Optical Microscopy Analysis Results from a Sample Study: Silver-copper alloy (Ag-Cu) and gold (Au) phases were identified on the surface. No corrosion products were detected, indicating excellent surface condition. Alpha-brass (Cu-Zn alloy) was identified. Despite minor corrosion traces, the surface remains well preserved. Chlorargyrite (AgCl) as silver corrosion products, cuprite (Cu2O) and tenorite (CuO) as copper corrosion products were detected. Additionally, paratacamite (Cu2(OH)3Cl) was identified. Acanthite (Ag2S) as silver sulfide corrosion, along with chlorargyrite and copper corrosion products (cuprite, tenorite), were dominant. The distribution of corrosion products indicates the object was strongly affected by environmental conditions.

Neutron Radiography Analysis Results from a Sample Study: Surface and internal structure examinations revealed a homogeneous, high-purity silver core beneath the surface coating of electrum coins. Traces of copper were detected in some samples, showing diffusion between the core and coating. Coating thicknesses ranged from 50 to 100 μm and were applied using a diffusion bağlama method. Limited copper diffusion between the coating and core was determined. Minor corrosion traces were found on the surface, indicating good preservation conditions. Electrum coins were generally well preserved, with only minor surface imperfections observed.

_{Neutron radiography image (}Source₎

The use of electrum coins eventually ceased for several fundamental reasons. First, the relatively low gold content in electrum alloy facilitated counterfeiting and further dilution of the alloy. This led to inflation and loss of trust in trade, prompting preference for more pure and controllable metals.

The naturally variable gold-to-silver ratio in electrum rendered the intrinsic value of each coin uncertain. This uncertainty created trust issues in trade and made standardizing the economic value of coins difficult. Pure gold and silver coins offered a more reliable solution by providing a standardized value.

Additionally, advances in metal refining technologies enabled the easy separation of gold and silver. These technological advances led to increased preference for pure gold and silver in coin production. Finally, states sought to control the composition of metals used in coinage to regulate their monetary systems. Electrum alloys, which complicated value control, were replaced by pure metals.

_{Electrum coin  (}Source₎

_{Electrum coin  (}Source₎

Today, electrum is used in certain still fields. In jewelry and decorative arts, artisans seeking to replicate ancient designs favor electrum. It is also used in the restoration of ancient artifacts or the production of replicas. This ensures that historical replicas maintain their original modern structure loyal. Although its use in monetary systems has ceased, electrum continues to retain importance in specific sectors due to its aesthetic and historical value.