The Role of Copper and Silver in the Colouration of Metallic Luster Decorations (Tunisia, 9th Century; Mesopotamia, 10th Century; Sicily, 16th Century): A First Approach

摘要

The metallic luster of glazed ceramics is a very special type of decoration. Its optical properties are characterized by a change of colour according to the observation conditions. In diffuse light, these decorations are often green, brown, or ochre-yellow. In specular reflection, they show an associated coloured metallic reflection (blue, golden-yellow, orange, etc.). Metallic copper and/or silver colloids almost always compose the metallic luster decorations. We wish to define the role of these two metals in the colouration observed both in diffuse light and in specular reflection. Our investigations show that a relationship exists between the proportions of copper and silver, and the diffuse colour. The green decorations contain more silver than copper, and the ochre-yellow and brown decorations contain more copper than silver. This specific correlation only exists if the samples have the same type of glaze and, especially, a similar chemical composition. This means that the composition of the glaze has an important influence in the colouration process. Moreover, our investigations show that there is no relationship between the specular colour and the overall concentration of copper and silver.