Paint characterization of Aguada Ambato potsherds (IV-XIIth centuries AD, Catamarca, Argentina) by BE image processing

V. GALVÁN; S. BERTOLINO; G. CASTELLANO; A. LAGUENS; A. RIVEROS

Cabo Frio

Congreso; XI Seminario Latinoamericano de Análisis por Técnicas de Rayos X (SARX 2008); 2008

Universidade Federal do Rio de Janeiro - Universidade Estadual do Rio de Janeiro

Scanning electron microscopy is a powerful technique in several fields of science and technology. In particular it is an important complement in the characterization of materials for which x-ray analysis is not possible. Such is the case of thin paint layers on ceramic pots, in which the interaction volume can be greater than the paint thickness, or the X-ray spectrum corresponding to the paint may not differ from the one corresponding to the ceramic body. This also occurs when the pigment matrix chemical composition is similar to that of the pot body. In this work, a new methodology for the treatment of SEM images with these characteristics was developed, in order to determine the chemical and mineralogical composition of black and white pigments of ceramic pieces belonging to the Ambato style of “Aguada” culture (Catamarca province, Argentina, 11th century AD). Backscattered electron images (BEI) normally provide information of mean atomic number in each region, but when the signal-to-noise ratio is low or the difference in the mean atomic number is less than 0.02%, chemical contrast may be imperceptible to human eye, since it can discriminate only about 30 from the 256 grey levels of an 8-bit image. The BEI images acquired for the samples studied showed no apparent contrast between black and white pigments. Through image processing algorithms using space and frequency filters, chemical contrast between pigments has been brought to evidence. The mineralogical differences between each pigment and ceramic body have been corroborated by quantification diagrams using the x-ray diffraction software TOPAS.