Chaux

La chaux provenant de plusieurs fours de l’Antiquité, du Moyen Âge et de l’époque moderne a été analysée par la diffraction des rayons X, au MEB-EDS et par la pétrographie. Cette chaux présente l’avantage d’être pure, et de ne pas avoir subie les changements chimiques qui ont lieu lors de l’ajout d’adjuvant pendant la fabrication des mortiers. Cette étude montre que les chaufourniers ont produit une grande diversité de chaux (grasses, maigres, hydrauliques, magnésiennes). La diffraction des rayons X, qui présente les résultats les plus prometteurs, éclaire de nombreux aspects des chaînes opératoires de production. Enfin, la mise en perspective de ces résultats avec les sources textuelles montre que la gamme des chaux répond à des besoins spécifiques à certaines filières économiques comme le bâtiment, l’agriculture ou l’industrie. Cet article pose donc les premiers jalons d’une histoire de la circulation et de la consommation des chaux entre l’Antiquité et l’époque moderne.

RESUMO
Em simultâneo com o estudo dos fornos de cal da região entre os rios Minho e Cávado, estamos a proceder à localização e registo dos exemplares ainda existentes em Portugal continental.
Damos conta do trabalho realizado até ao momento, abordando as referências mais antigas acerca desta indústria no país, o seu registo na toponímia e cartografia, a variabilidade tipológica e o seu enquadramento nacional.
Apresentamos ainda os resultados preliminares relativos à região do Minho/Cávado, através dos quais, para além da identificação e localização dos fornos existentes, se constata que a matéria-prima necessária para produzir a cal nem sempre se encontra próxima dos locais de produção.

ABSTRACT
While studying the limekilns in the region between the rivers Minho and Cávado, we are also localizing and registering the examples that exist in Continental Portugal.
We take in to account the studies completed up to this date, addressing the oldest references about this industry in the country, their record in place names and cartography, the typological variability and their national framework.
We also present the preliminary results from the region of Minho/Cávado, due to which, by identifing and locating the existing limekilns, it is possible to observe that the necessary raw material to produce lime is not always in proximity to the production sites. "

Palavras-chave: cal, fornos de cal, arqueologia industrial
Keywords: lime, limekilns, industrial archaeology

The indices of the lime manufacture and treatment frequently appear on the archaeological sites, from the places of limestone extraction to the building sites. A first assessment is tried here, with consideration to the economic choices and techniques which can intervene in each stage of the operational chain.
It seems that the production of lime could form part of the economic activities of the Gallo-Roman villae, but the majority of the structures of combustion would be localised near the sites of extraction of limestone.
The extinction of the quicklime was done mainly by immersion in pits. These structures are rare on the sites of extraction and frequent near constructions. Thus, the lime dispatched on the building sites was quicklime. The conservation of extinct lime was done in the pits. Another structure, lime vat, was smaller and probably employed over the long duration, and was reactivated regularly according to the requirements out of mortar. It allowed in particular the temporary conservation of extinct lime between two phases of construction or maintenance of the building.
Lastly, it appears that the mixing of the mortar was generally carried out on the ground, after just a simple cleaning of surface.