Influence of Manufacturing Processes in Deterioration of Ag-Cu Artefact Alloy

Abstract

Ancient silver with about 2% copper object is studied to determine manufacturing defects based on chemical and microscopic investigations. In this paper Bullion (silver-copper alloy) ink box inlays with enamel from the Museum of the faculty of applied arts in Cairo, Egypt has been investigated to identify manufacturing process and its effect on the ink deterioration. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometry (SEM-EDS) method has been used on samples to reveal chemical composition of the alloys and the effect of various fabrication and thermal treatment. The results indicated that all samples were made of silver-copper alloys, other elemental corrosion layers have detected in contents such as C, O, S, Cl, Si, Na, Ca, Al. Fracture surfaces provide with important information helping to recognize failure causes, so the fracture surface investigation and etching by means of alcoholic ferric chloride was carried out for microstructural analysis. Scanning Electron Microscopy SEM-micrograph of etching sample showed pores and cracking propagation. Crack initiation usually appears at the object surface, and is generally produced by stress concentrators, producing rise to local plastic deformation or cracking and detachment of brittle precipitates. Local stress-strain concentration related to a variety of microstructural inhomogeneities. The X-ray diffraction analysis (XRD) confirmed the EDX analysis that the corrosion compounds consist of Montmorillonite NaO 3 (Al, Mg) 2 Si 4 O 10 (OH) 2 XH 2 O, Atacamite Cu 2 Cl(OH) 3 , Malachite Cu 2 CO 3 (OH) 2 , Paratacamite Cu 2 Cl(OH) 3 , Cuprite Cu 2 O, Acanthite Ag 2 S, Tenorite CuO, Calcite CaCO 3 , Chlorargyrite AgCl, Copper Cu. Silver-copper alloys failed through corrosion process that produce brownish-black tarnish. This tarnish alters the aesthetic of the object. The corrosion layers of the object referred to long-term contamination and oxidation, which led to increase intergranular cracking, regions of ductile fracture, and brittle intergranular fracture.

Characterization of a Set of Coin Silver Spoons of Prince Mohamed Ali

“…9 (2023) millennium BC [6]. The Binary Alloy, which is composed of an alloy of silver and copper and named Bullion alloy [7] is one of the most popular silver alloys [8,9] and there is a percentage of impurities from tin, arsenic, lead, and antimony [10]. The corrosion process, which results in a brownishblack tarnish, is responsible for the deterioration of silver-copper alloys.…”