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Calcium oxalates and prehistoric paintings. The usefulness of these biomaterials

A. HERNANZ1,* , J. M. GAVIRA-VALLEJO1, J. F. RUIZ-LÓPEZ2

Affiliation

  1. Departamento de Ciencias y Técnicas Fisicoquímicas, Facultad de Ciencias, Universidad Nacional de Educación a Distancia (UNED), Senda del Rey, 9, E-28040 Madrid, Spain
  2. Departamento de Prehistoria y Arqueología, Facultad de Geografía e Historia, UNED, Senda del Rey, 7, E-28040 Madrid, Spain

Abstract

Oxalate accretions of whewellite (CaC2O4.H2O) and weddellite (CaC2O4.(2+x)H2O, x ≤ 0.5) have been found by Raman microscopy on Post-Palaeolithic rock paintings from open-air rock shelters of Triassic sandstone in the Sierra de las Cuerdas (Cuenca, Spain). Scanning electron microscopy (SEM) of these accretions suggests that they could have been produced by colonies of lichens that lived on the rock surface. Raman and petrologic microscopy of samples from a painting panel has revealed the nature and distribution of the components: α-quartz, haematite, whewellite, gypsum, muscovite, microcline, anatase and rutile. Energy-dispersive X-ray (EDX) spectroscopy confirms these results. The observed microstratigraphic oxalate layers are very helpful for archaeological studies. The pigment, haematite, is located between two of them and some superimposition of pictographs or repainting processes have been detected. The observed oxalate layers protect these works of art, prevent weathering and have been used for the first AMS 14C dating of Post-Palaeolithic rock art in Spain..

Keywords

Whewellite, Weddellite, Prehistoric paintings, Raman microscopy, SEM/EDX.

Submitted at: Nov. 15, 2006
Accepted at: March 15, 2007

Citation

A. HERNANZ, J. M. GAVIRA-VALLEJO, J. F. RUIZ-LÓPEZ, Calcium oxalates and prehistoric paintings. The usefulness of these biomaterials, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 3, pp. 512-521 (2007)