Influence of local mineral raw materials on the commercial success of Aveiro production of ancient ceramic sugar jars

Abstract

Ceramic sugar jars played a paramount role in the sugar production cycle, being used for the maturation of the sugar. These pieces were conic having a hole at the bottom, being used specifically for the stage of the purge of the sugar cake. From the 15th until the beginning of the nineteenth centuries, the old pottery centres from Aveiro and Lisbon regions (Portugal) produced heavily these “formas de açúcar” (“sugar jars”), which were exported to sugar production areas, at places as diverse as Madeira, Canaries, Cape Verde, Cuba and Brazil. Mineralogical and chemical data obtained in samples from Aveiro point to local production, using the upper Cretaceous (Maastrichtian) marly (dolomitic) clays and clayey sands as primary raw materials. Ceramics from Barreiro (Lisbon) are generally more silicated and less carbonated, a composition close to the Tagus Cenozoic Basin clays. The higher iron content of Aveiro clays favours the glazing of ceramic paste at lower temperatures, giving better mechanical resistance, which can justify “their best quality”. This study highligths the influence of local mineral raw materials on the technological characteristics of produced sugarware and the actual reasons that allowed Aveiro sugarware production to be competitive to Lisbon (Barreiro) one.