On the first evidence of gum guaicum and its use as finishing pigment on Brasilian ceramics

This study reports a multi-analytical investigation on two ceramic bowls from the 19th-century Brazilian production, belonging to the Kadiweu culture (Rio Nabileque, Mato Grosso do Sul) and currently preserved at MUCIV (Museo della Cività, “Museo Etnografico L. Pigorini” section) in Rome [1]. X-ray radiography was used to define the execution technique. Optical microscopy on thin section and X-ray diffraction (XRD) were used to characterize the ceramic production in terms of raw materials, firing and production process. UV observation and micro-Fourier Transform Infrared spectroscopy (µ-FTIR) were used to highlight the presence of restoration or protective products. Results showed that raw materials and technology are compatible with the local production [2]. The use of grog was documented for the ceramic paste, which was in part shaped by the coiling technique and then fired at moderately high temperatures and decorated with a white calcic pigment. The most striking finding was the identification of the so-called gum guaicum – or guaiac resin -, most likely used as a black pigment [3] during the last production steps, its spectrum being for the first time collected on ceramics. The use of a resin from “pau-santo” (Brazilian Blackheart or holy wood) as a pigment for blackish areas has been documented on the corresponding contemporary production, where it is extracted and eventually mixed with mastic for darker hues.