Micro-Raman study of red decorations in French faiences of the 18th and 19th centuries.

International audienceObtaining the red color was a technical and economic challenge for the French faience manufactories in the 18th and 19th centuries. The tendency of the red hematite to turn into drab brown during the firing process explains the difficulty in obtaining this color. Red decorations in shards coming from the four production centers of faience manufacturing during this period – Rouen (northwest), Nevers (central), Thiviers (southwest) and Argonne (northeast) – have been studied by means of micro-Raman spectroscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Among them, Thiviers appears to be the leader thanks to a particular reddish sandstone called ‘Gr`es de Thiviers' (GT) available in the region. This material is composed of a-quartz grains cemented by goethite (a-FeOOH), leading to red hematite during the firing process. Raman spectra revealed that GT was also used by the Nevers manufactories in the middle of the 19th century instead of other methods used in the middle of the 18th century based on the mixture of Naples yellow with iron oxides. Manufactories in the north of France at Rouen and Argonne did not employ GT, but Naples yellow together with iron oxides or other pigments as ‘bol d'Arm´enie'