Analytical study of waterlogged ivory from the Bajo de la campana site (Murcia, Spain)

[EN] This work reports an analytical study conducted prior to the conservation intervention of a collection of elephant tusks excavated from a wreck site of a 600-500 BC Phoenician trading vessel in Bajo de la campana (Murcia, Spain). The conservation state of ivory, determined by prolongated immersion in a marine environment, was established by a multi-technique methodology: light microscopy, field emission scanning electron microscopy X-ray microanalysis (FESEM-EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), spectrophotometry and gas chromatography-mass spectrometry (GC-MS). The analyses demonstrated that the structure and composition of both tusk parts, namely the inner ivory and outer cementum, were altered due to characteristic diagenetic processes of a marine environment. Ca enrichment was observed in both tusk parts, which gave higher Ca/P molar ratio values than for ideal hydroxyapatite. Mg leaching was observed, together with uptake of exogenous elements (F, Cl, Si, Al, S, Na, Fe, Cu, Sr, Pb, Sn, Ag, V, Ni, Cd and Zn), which were prevalently identified in the external tusk part. Uptake of S and Fe was associated with the neoformation of pyrite framboids. The high carbonate content measured by FTIR, which agreed with the higher Ca/P ratios found in the archaeological tusk, was ascribed to the carbonate substitution of phosphate groups (type-B) in the bioapatite accompanied by some authigenic calcium carbonate that infilled ivory. An increased degree of crystallinity was observed when comparing the values of several crystallinity indices found in the archaeological bioapatite with those of a modern tusk, used as the reference material. Increased crystallinity prevalently took place in the cementurn. In accordance with increased crystallinity, the HPO42- content index indicated that the hydrated layer of bioapatite nanocrystals diminished in the archaeological tusk, and prevalently in the cementum. All these changes correlated with the significant organic matter loss reported for the archaeological tusk. Interestingly, remaining collagenous matter noticeably altered with enrichment in glycine and depletion in acid amino acids. Changes in the secondary structure of proteins were also recognised and associated with collagen gelatinisation. In addition to proteinaceous materials, small amounts of long-chain fatty acids, monoglycerides and cholesteryl oleate were identified by GC-MS. Cholesteryl oleate was associated with blood, which could have precipitated at the time of specimen death. The identification of large amounts of pyrite framboids and the high oleic acid/palmitic acid ratio in the archaeological tusk suggested minimal oxidative degradation processes, probably due to the slightly anoxic conditions of the underwater Bajo de la campana site environment. (C) 2016 Elsevier B.V. All rights reserved.The authors wish to thank CITES Espana and Direccion General de Bienes Culturales y Ensenanzas Artisticas, de la Consejeria de Educacion, Cultura y Universidades de la Comunidad Autonoma de la Region de Murcia, Museo Nacional de Arqueologia Subacuatica. Financial support is gratefully acknowledged from Spanish "I + D + I MINECO" projects CTQ2011-28079-CO3-01 and 02 and CTQ2014-53736-C3-1-P supported by ERDEF funds. The authors also wish to thank Mr. Manuel Planes and Dr. Jose Luis Moya, technical supervisors of the Electron Microscopy Service of the Universitat Politecnica de Valencia.Domenech Carbo, MT.; Buendía Ortuño, MDM.; Pasies Oviedo, T.; Osete Cortina, L. (2016). Analytical study of waterlogged ivory from the Bajo de la campana site (Murcia, Spain). Microchemical Journal. 126:381-405. https://doi.org/10.1016/j.microc.2015.12.022S38140512

Aportación de nuevas metodologías multitécnica en el estudio y conservación de patrimonio numismático de procedencia subacuática

his paper presents a study of the conservation status of copper-based coins from the National Museum of Underwater Archaeology. The multitechnical methodology includes conventional instrumentation such as optical microscopy, FTIR spectroscopy and advanced non-invasive techniques such as microparticle voltamperometry and focused ion beam -FESEM-EDX. Thus it has been possible to identify the type of alloy, corrosion products, surface deposits and old interventions. It should be noted the identification of atypical alteration mechanisms such as the formation of carboxylated complexes of metal ions generated in the electrochemical processes of corrosion of the metal or alloy and the lipid materials fixed on the surface of the coin when it was in circulation and that, due to its hydrophobic character have been preserved in the underwater environment in which the coins have remained for centuries. These findings have been very useful to establish the most suitable conservation treatments for these pieces.ste artigo apresenta um estudo do estado de conservação de moedas à base de cobre provenientes do Museu Nacional de Arqueologia Subaquática. A metodologia multitécnica inclui instrumentação convencional, como microscopia ótica, espectroscopia FTIR e técnicas avançadas de não invasivas, como voltamperometria de micropartículas e feixe de iões focado - FESEM-EDX. Assim, foi possível identificar o tipo de liga, produtos de corrosão, depósitos superficiais e intervenções antigas. Deve-se destacar a identificação de mecanismos atípicos de alteração, como a formação de complexos carboxílicos de iões metálicos gerados nos processos eletroquímicos de corrosão do metal ou liga e os materiais lipídicos fixados na superfície da moeda quando ela estava em circulação e que, devido ao seu caráter hidrofóbico, foi preservado no ambiente subaquático em que as moedas permaneceram por séculos. Estas descobertas foram muito úteis para estabelecer os tratamentos de conservação mais adequados para essas peças.Este trabajo presenta un estudio del estado de conservación de monedas con base de cobre procedente del Museo Nacional de Arqueología Subacuática. La metodología multitécnica incluye instrumentación convencional como microscopía óptica, espectroscopia FTIR y técnicas avanzadas nanoinvasivas como voltamperometría de micropartículas y haz de iones focalizados-FESEM-EDX. Así se ha podido identificar el tipo de aleación, productos de corrosión, depósitos superficiales y antiguas intervenciones. Cabe señalar la identificación de mecanismos de alteración atípicos como la formación de complejos carboxilados de iones metálicos generados en los procesos electroquímicos de corrosión del metal o aleación y los materiales lipídicos fijados en la superficie de la moneda cuando esta estuvo en circulación y que gracias a su carácter hidrófobo se han conservado en el ambiente subacuático en el que las monedas han permanecido durante siglos. Estos hallazgos han resultado de gran utilidad para establecer los tratamientos más idóneos de conservación de estas piezas.