The sacred source known as Flere Havens, as referred to by the Etruscans, has yielded numerous bronze artifacts over the years of excavation. These ex-votos reflect the ritualistic and curative importance attributed to the thermal waters that emanated from this location. Since the dawn of humanity, bronze has been the preferred alloy for the creation of artifacts such as utensils, jewelry, and works of art, with a particularly abundant use in statuary. What has made bronze so popular throughout history? To answer this question, one must consider the quality and versatility of this alloy. Bronze is known for its mechanical properties, including resistance, toughness, and workability, as evidenced by the bronze sheet fragments discovered at the site of San Casciano dei Bagni. It is malleable and has a melting point compatible with temperatures achievable through the use of charcoal. Furthermore, its corrosion resistance, a chemical characteristic of bronze, has allowed many works to survive to the present day. A significant factor that should be considered is color. The introduction of tin into copper dramatically changes its color characteristics. Copper is known for its distinctive pink hue, which turns red or brown upon oxidation. As tin is added, the alloy's color shifts from copper's pink to a yellowish bronze, reaching a yellowish hue at approximately 16% tin content, and moving toward silver as the tin content exceeds this threshold. Lead also plays a crucial role in the technological property of castability, lowering the melting point and increasing capillarity. Its impact on detail reproduction is being studied, especially regarding its insolubility in copper and its alloys. Lead increases machinability simplifying turning, chiseling, and engraving. However, when present in excess, lead hinders workability via mechanical deformation. The effect of lead on corrosion resistance is well-documented, with higher lead content decreasing resistance, especially due to the formation of nodules that can protrude. Regarding color, the presence of lead does not significantly affect the color but leads to the dulling of the alloy's surface. The study of the bronzes found at San Casciano dei Bagni has allowed for the exploration of the aspects in case studies characterized by consistent production purpose and stratigraphy. This research focused on two essential aspects of the metallic material: the alloy, analyzed both in terms of major element concentrations and metallurgical state (linked directly to the manufacturing process), and the response to environmental degradation and exposure conditions. In this case, the artifacts' condition reflects an interaction between the alloy and its environment, leading to alterations due to interaction with thermal waters and mud, as well as protective treatments where applicable. The color of the bronze before deposition results from all the stages, from casting (cooling rate) to surface finishing, with explicit aesthetic purposes and implicit effects on corrosion resistance. Upon discovery, the color reflects the various alteration processes that took place over the artifact's prolonged exposure to an environment rich in sulfates and low in oxygen, characteristic of the anaerobic conditions and bacterial colonies capable of surviving in these environments. The constant presence of water and temperatures around 40°C accelerates these alterations but results in patinas that are often passive enough to limit the damage typically caused by corrosion. The study incorporated various analytical techniques, including compositional analysis (LIBS, XRF, SEM-EDXS), metallographic characterization, electrochemical studies, and colorimetry on lab-produced alloys. These techniques allowed for precise mapping of the alloys’ composition, identifying elemental variations, corrosion layers, and manufacturing processes. Electrochemical studies, including the use of a newly developed electrochemical probe for localized corrosion, identified areas most prone to alteration. Furthermore, colorimetric analysis revealed valuable information on the alloys’ chromatic characteristics, which were compared with those of alloys produced in the laboratory to replicate historical compositions. Laboratory-based alloy casting and subsequent colorimetric measurements highlighted the full spectrum of compositions within the solubility range of tin in copper, revealing a boundary between potential monophase alloys and those that required more complex, multiphase structures. This distinction is essential for understanding the manufacturing choices made in ancient times. In conclusion, the study of bronze artifacts from San Casciano dei Bagni provides new insights into ancient metallurgical practices, the materials durability, and the environmental factors that have influenced their preservation.
Il santuario ritrovato 3. Oltre il bronzo. Rapporto preliminare di Scavo (2023-2024) al Bagno Grande di San Casciano dei Bagni.
Paolo Piccardo;Flavia Boragina;Matilde Pedemonte;Roberto Spotorno
2025-01-01
Abstract
The sacred source known as Flere Havens, as referred to by the Etruscans, has yielded numerous bronze artifacts over the years of excavation. These ex-votos reflect the ritualistic and curative importance attributed to the thermal waters that emanated from this location. Since the dawn of humanity, bronze has been the preferred alloy for the creation of artifacts such as utensils, jewelry, and works of art, with a particularly abundant use in statuary. What has made bronze so popular throughout history? To answer this question, one must consider the quality and versatility of this alloy. Bronze is known for its mechanical properties, including resistance, toughness, and workability, as evidenced by the bronze sheet fragments discovered at the site of San Casciano dei Bagni. It is malleable and has a melting point compatible with temperatures achievable through the use of charcoal. Furthermore, its corrosion resistance, a chemical characteristic of bronze, has allowed many works to survive to the present day. A significant factor that should be considered is color. The introduction of tin into copper dramatically changes its color characteristics. Copper is known for its distinctive pink hue, which turns red or brown upon oxidation. As tin is added, the alloy's color shifts from copper's pink to a yellowish bronze, reaching a yellowish hue at approximately 16% tin content, and moving toward silver as the tin content exceeds this threshold. Lead also plays a crucial role in the technological property of castability, lowering the melting point and increasing capillarity. Its impact on detail reproduction is being studied, especially regarding its insolubility in copper and its alloys. Lead increases machinability simplifying turning, chiseling, and engraving. However, when present in excess, lead hinders workability via mechanical deformation. The effect of lead on corrosion resistance is well-documented, with higher lead content decreasing resistance, especially due to the formation of nodules that can protrude. Regarding color, the presence of lead does not significantly affect the color but leads to the dulling of the alloy's surface. The study of the bronzes found at San Casciano dei Bagni has allowed for the exploration of the aspects in case studies characterized by consistent production purpose and stratigraphy. This research focused on two essential aspects of the metallic material: the alloy, analyzed both in terms of major element concentrations and metallurgical state (linked directly to the manufacturing process), and the response to environmental degradation and exposure conditions. In this case, the artifacts' condition reflects an interaction between the alloy and its environment, leading to alterations due to interaction with thermal waters and mud, as well as protective treatments where applicable. The color of the bronze before deposition results from all the stages, from casting (cooling rate) to surface finishing, with explicit aesthetic purposes and implicit effects on corrosion resistance. Upon discovery, the color reflects the various alteration processes that took place over the artifact's prolonged exposure to an environment rich in sulfates and low in oxygen, characteristic of the anaerobic conditions and bacterial colonies capable of surviving in these environments. The constant presence of water and temperatures around 40°C accelerates these alterations but results in patinas that are often passive enough to limit the damage typically caused by corrosion. The study incorporated various analytical techniques, including compositional analysis (LIBS, XRF, SEM-EDXS), metallographic characterization, electrochemical studies, and colorimetry on lab-produced alloys. These techniques allowed for precise mapping of the alloys’ composition, identifying elemental variations, corrosion layers, and manufacturing processes. Electrochemical studies, including the use of a newly developed electrochemical probe for localized corrosion, identified areas most prone to alteration. Furthermore, colorimetric analysis revealed valuable information on the alloys’ chromatic characteristics, which were compared with those of alloys produced in the laboratory to replicate historical compositions. Laboratory-based alloy casting and subsequent colorimetric measurements highlighted the full spectrum of compositions within the solubility range of tin in copper, revealing a boundary between potential monophase alloys and those that required more complex, multiphase structures. This distinction is essential for understanding the manufacturing choices made in ancient times. In conclusion, the study of bronze artifacts from San Casciano dei Bagni provides new insights into ancient metallurgical practices, the materials durability, and the environmental factors that have influenced their preservation.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
