Minero-petrographic characterisation of historic bricks in the Arsenale, Venice Fabrizio Antonelli *, Stefano Cancelliere, Lorenzo Lazzarini Laboratorio di Analisi dei Materiali Antichi, Dip. di Storia dell’Architettura, IUAV, Venice, Italy Received 20 December 2001; accepted 21 January 2002 1. Introduction This first stage of the study involved the analysis of 12 samples of bricks belonging to different phases in the construction of the internal walls of Tesone 105 in the Venice Arsenale, spanning about three centuries (XVI–XIX). The samples were selected in conjunction with the other members of the project team with a view to achieving a comprehensive, coordinated assessment of the nature and state of conservation of all the building materials used in the sample building mentioned above. The purpose of the investigation was to make a basic mineralogical and petrographic characterisation of the mix- tures of materials used to make the bricks; further aims include enhancing knowledge of the building’s physical history and providing useful data for decisions regarding restoration work on the Tesone, currently being planned as an exemplary and illustrative project for the conservation of the Arsenale as a whole. It is hoped that the data presented with this short note may also prove useful for future comparisons with other types of historic brick in Venice and as a source of information on the history of the technology of brick production in Venice. 2. Methods of study Samples were taken from various parts (phases) and levels (stratigraphic units) of the inner walls of Tesone 105 – the north, south, east and west sides ( Table 1). The samples were studied using standard methods of minero-petrographic analysis (observation of thin sections with an optical microscope and diffractometric analysis of X-rays performed with a Philips PW 1830 diffractometer: radiation Cu Kα/Ni at 40 Kv and 20 mA). 3. Results and discussion On the basis of the minero-petrographical analyses (Tables 2, 3), the bricks selected for study may be subdi- vided into two groups: The first comprises just two samples (ARS 2 and 7) of albasi bricks, which feature a yellowish impasto and were probably reused. They were made from calcareous – pre- sumably kaolinitic – clays, without other additions and were baked at 700–750 °C, i.e., at temperatures below the point at which the calcite content begins to dissociate. In fact, when observed in thin sections, the calcite always appeared well-preserved (Fig. 1a). The bricks in this group are composed of a paste microscopically with aggregate polarisation (c.f. Fig. 1a) which contains bonherz (Fig. 1b), sometimes also calcare- ous (ARS 7), and of a very weak sandy skeleton (≤ 5%) which is coincident with the detritic fraction of the basic clays. The sandy skeleton features fine, serial grains and is mainly of a calcareous nature (micritic clasts and bioclasts); it also contains secondary quantities of angular and poly- crystalline quartz, chert, pyroxene and potassium mica. In sample ARS 2 diffractometric analysis (Table 2) re- vealed the presence of significant amounts of aragonite, which most likely originated from dissolution/ recrystallisation cycles of CaCO 3 in the presence of organic substances (probably algae) from the mortar in the joints. The second group comprises the rest of the samples (ARS 1, ARS 3-6, ARS 8-12), all of which are ferrioli bricks, with an impasto of an intense red colour and made basically with illitic clays baked at between 800 and 850 °C. The groundmass features aggregate polarisation and in- cludes variable quantities of bonherz which in one sample * Corresponding author. E-mail address: lama@iuav.it (F. Antonelli). Journal of Cultural Heritage 3 (2002) 59–64 www.elsevier.com/locate/culher © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 2 9 6 - 2 0 7 4 ( 0 2 ) 0 1 1 6 0 - 3