Characteristics of the Raman spectra of archaeological Malachites

Abstract

Archaeological malachites, represented by the malachites found on the ancient Chinese and Vietnamese copper/bronze coins, may also incorporate those on other archaeological objects. The Raman spectra with Ar laser of these malachites differ slightly from those of the natural malachites found in mines. In this study, 120 measurements of the malachites on 40 coins identified 26 bands, while only around 18 of them are frequently observed. The wavenumbers (cm À1 ), shifts (AE)and relative intensities (in parentheses) of the 18 common bands read, respectively: 153AE4 (0-vs), 179AE7 (m-vs), 217AE8 (m-vs), 274AE7 (0-vs), 355AE5 (0-m), 431AE4 (0-vs), 514AE3 (0-m), 533AE5 (0-s), 566AE3 (0-m), 599AE2 (0-m), 718AE6 (0-m), 754AE2 (0-m), 1061AE7 (0-m), 1093AE10 (0-m), 1365AE9 (0-m), 1491AE7 (0-vs), 3321AE11 (0-vs) and 3380AE7 (0-vs).In comparison with those of the 105 measurements on the natural malachites in five mines, the Raman spectra of the archaeological malachites tend to show less bands, higher backgrounds and greater shifts in the wavenumber position. The weakening or loss of bands is in the order of the OH stretch (3300 cm À1 ) (most severe), CO 3 (600-1500 cm À1 ) and CuO (<600 cm À1 ) (less severe) groups, indicating successive stages of corrosion. The malachites on the coins from three climate zones show their own characteristics. Several coins may have experienced two or more climatic or geologic episodes and show complex Raman spectra different from those of the natural malachites.

Raman spectroscopy of green minerals and reaction products with an application in Cultural Heritage research

“…Moreover, green Cu containing salts are found as degradation products of copper or bronze artifacts, or of Cu containing pigments . The formation of chlorides, sulphates, phosphates and mixed salts is related to a variety of environmental and intrinsic factors, so that the presence of specific secondary minerals is related to local conditions leading to degradation and to the stability of the compounds …”

Occurrence of phosphatic corrosion products on bronze swords of the Warring States period buried at Lijiaba site in Chongqing, China

“…3 are also associated with this mineral [22,23]. The presence of cuprite peaks within the malachite spectrum is a common phenomenon in Raman spectroscopy of archaeological malachite, due to the close association of the two phases in copper corrosion processes [21].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part VIII

“…In comparison with the natural malachites in five mines, the Raman spectra of the archeological malachites tend to show fewer bands, higher backgrounds and greater shifts in the wavenumber position. [170] Zhao and coworkers characterized microcrystals in some ancient glass beads from China by means of confocal Raman microspectroscopy. The beads were excavated from different regions of China, including Xinjiang, Henan, Hubei, and Guangxi Provinces, and were dated mainly from the 10th century BC to the 9th century AD.…”

“…Variations from phonon intensity ratios reveal obvious anomalies with the decreasing temperature, indicating the existence of strong electron-phonon coupling mediated by Froehlich interaction below 200°K. [226] Phases and phase transitions Beuvier and coworkers studied phase transformations in CaCO 3 / iron oxide composite that were induced by thermal treatment and laser irradiation. They show that the phase transformations observed by x-ray diffraction are also observed under laser irradiation as a consequence of the absorption of the laser irradiation by iron oxide NPs.…”

“…studied the characteristics of the Raman spectra of archeological Malachites. In comparison with the natural malachites in five mines, the Raman spectra of the archeological malachites tend to show fewer bands, higher backgrounds and greater shifts in the wavenumber position . Zhao and coworkers characterized microcrystals in some ancient glass beads from China by means of confocal Raman microspectroscopy.…”