AbstractLead‐containing raw glazes were applied on biscuit tile and fired at cones 02, 2, and 4. The glaze body interface was examined microscopically by preparing thin cross sections. The powdered glassy portion was also investigated.Because the crystals separating at the interface were frequently too small for satisfactory study, a technique for promoting their growth was used. Anorthite, wollasto‐nite, gehlenite, undissolved quartz, tridymite, and cristobalite were observed.The effects of altering the bases and the alumina and silica content of the glaze were studied, and the amount and the effect of the solution of the body were examined. The authors conclude that the interfacial layer is not necessarily intermediate in expansion cond