Egyptian faience glazing by the cementation method part 1: an investigation of the glazing powder composition and glazing mechanism

摘要

In cementation glazing, for various reasons, there are significant differences between the composition ofthe glass phases present in the faience microstructure and the glazing powder composition. Furthermore,in this glazing method, the glazing powder should perform more functions, which are: producinga shiny and smooth glaze coating, producing a firm capsule surrounding objects entirely (to preventadhesion between sintered glazing mixture and the melting glaze coating), and, finally, producinga porous and friable sintered glazing mixture for safe and easy removal of buried objects. It is obviousthat these functions also have significant effects on the glazing powder composition and constitution.Therefore, analytical data on faience glass phases are very unlikely to reflect the strict composition andconstitution of the original glazing powder properly. Accordingly, the composition and constitution ofcementation glazing powder have remained obscure for a long time. These data are particularly crucialfactors for cementation replication experiments and, consequently, for our awareness of the ancientfaience production. In this paper, a series of cementation replication experiments have been conducted inan attempt to provide further clarification of these issues. In addition, as a comparative indicator foralkali and copper vaporisation, a small piece of rock quartz was placed separately above the glazingpowder. After firing, the appearance of the faience objects and quartz pieces and the microstructures andchemical compositions of a select group of samples, obtained using Scanning Electron Microscopy eEnergy Dispersive Spectroscopy (SEM-EDS), were investigated. The discussion has focused mainly onissues such as the raw materials and their contribution in the glazing process, the criteria for determiningthe faience glazing methods, the necessary quantity of alkalis for a successful cementation glazing, and,particularly, the glazing mechanism.