Coloured metallic shine associated to lustre decoration of glazed ceramics: a theoretical analysis of the optical properties

Metallic lustre decoration is not a common decoration of glazed ceramics. Its peculiarity is the appearance of a coloured metallic shine, when the observation is made in specular reflection. This decoration was quite often used for dishes and architecture during the Medieval Islam period. In this work, we show that the elementary composition of the decoration (metallic-copper-and-silver colloids) is an essential parameter but does not explain everything. From the Maxwell Garnett theory, we establish that the feature of the reflectance spectra of coloured metallic shines also depends on the colloidal texture of copper and silver and on the refractive index of the glaze. Finally, we obtain a good agreement between both theoretical and experimental spectra, which validates the proposed theoretical model.