Influence of ZnO addition on the elimination of discoloration in reformulated bone China

Abstract

The quality of bone china is determined by its high degree of whiteness. A creamy white is the ideal colour. Bone china owes its whiteness to the bleaching action of P<inf>2</inf>O<inf>5</inf> which is incorporated into the microstructure by bone ash present in bone china compositions. Typical composition of a modern commercial bone china is 25 wt% clay, 25 wt % of cornish stone and 50 wt % bone ash. There have been numerous studies on reducing the bone ash content of bone china, however, whenever this was attempted there was always an undesired discoloration. In this study, new formulations with a lower bone ash content were prepared and once more it was observed that fired samples of reformulated bone china had a bluish-green tint. However, when ZnO was added to the lower bone ash containing bone china formulation this bluish-green tint was removed. It was clearly shown that ZnO containing reformulated bone china bodies develop Zn-spinel crystals, which are thought to be the reason for the increasing whiteness of samples. The lack of iron inclusions might be explained by iron incorporation into the spinel structure. © 2020 Elsevier B.V., All rights reserved.