Copper red glazes: a coating with two families of particles

TL;DR

This study investigates the origin of the deep red color in copper glazes on ceramics by analyzing the structure and optical properties of copper nanoparticles, revealing two particle families that influence color through absorption and scattering.

Contribution

It provides a comprehensive explanation of the color mechanism in copper glazes by combining TEM, EELS, optical characterization, and modeling, identifying two distinct nanoparticle populations.

Findings

Two families of copper nanoparticles identified: small particles cause absorption, larger particles cause scattering.

The color results from a combination of absorption and scattering effects by these nanoparticles.

A theoretical color chart for various hues in copper glazes has been developed.

Abstract

In order to explain the origin of the deep red color of copper glazes on ceramics, a ceramist has elaborated, by firing under reducing atmosphere, a significant number of tiles. The analysis of the structure and composition of a representative sample by TEM and EELS, followed by an optical characterization and an optical modeling using the radiative transfer approach (four-flux model) have enabled a comprehensive explanation of the origin of the color in these glazes. The presence of two families of copper nanoparticles in the vitreous matrix. The first, purely absorbing, of diameter 10-50 nm, essentially creates color by a substractive process. The second, due to its larger diameter, 100 nm or more, mainly acts on color by scattering of the visible light. Both act competitively in the layer. A color chart of all the hues which can be reached by this technique has eventually been theoretically calculated.