Quantitative comparisons of the color of CuAs, CuSn, CuNi, and CuSb alloys

Abstract

The colors of copper alloys are of particular interest in archaeology and can be characterized quantitatively and systematically. The CIELAB color system can determine different color parameters such as a*, b*, and L* by means of a spectrophotometer that describes the surface color. Additional information such as C* and h values can be calculated from these parameters which allows one to build a set of color-composition diagrams that connects chromaticity and alloy composition. With such data it is possible to estimate the color of prehistoric metal artifacts with similar chemical composition. A better understanding of the association between metallurgical composition and color will aid the research of prehistoric metalwork because choices in production and use of metal were likely influenced by this particular quality of metal.

Ein Kupfergusskuchen mit hohem Antimongehalt aus Velem/Westungarn

“…Auffällig ist, dass die Schnittfläche silbrig aussieht und nicht kupferfarben andere Kupfergusskuchen aus Fahlerzen mit Arsengehalt eindeutig kupferfarben sind [9,10], erzeugte dies anfängliche Zweifel, ob es sich tatsächlich um einen Kupfergusskuchen handelt. Diese Zweifel wurden jedoch durch erste Messungen der Zusammensetzung ausgeräumt und offensichtlich bestimmen die Legierungselemente Sb und As die silbrige Farbe dieser Legierung [11]. Eine RFA Analyse an einer Schnittfläche ergab etwa 83 Gew.% Cu, 10 Gew.% Sb, 4,5 Gew.% As und je 1,2 Gew.% S und Ag.…”

The Provenance, Use, and Circulation of Metals in the European Bronze Age: The State of Debate

“…Thus, depending on the desired function of a new object, as well as its aesthetic appeal (cf. Mödlinger et al 2017;, the production process from raw or recycled metal must have required different levels of control.…”

Beyond Provenance

“…Many archaeological artefacts contain alloying elements below such levels, and yet higher than would be expected if the sole source of such elements were contaminants in the copper ore sources. There has been much useful work recently relating the colour of the metal to the composition (e.g., Hosler 1995, Kuijpers 2013, Mödlinger et al 2017, which has important implications for understanding the question of intentionality. Although we do not dispute for a moment that certain alloyed metals in antiquity were designed so as to achieve particular physical properties or a desired appearance of the finished product, it is the information contained in the 'non-standard' alloys that we particularly wish to capture by using a different approach.…”