Two electron microprobe techniques were used to study factors that contribute to the failures of fireclay condensers in a horizontal zinc-reduction smelter. One method involved studying photographs of oscilloscope displays of x-ray intensity profiles of individual elements. This enabled determination of the elements present in the interface area between fireclay condensers and a hard adherent deposit which results from reaction with zinc vapors. The major elements were found, as well as their locations and extent of interaction with each other. Another electron microprobe technique, color composite scanning, was used to identify properly the locations of compounds resulting from reactions of elements at the fireclay-deposit interface. X-ray diffraction examination verified the electron microprobe findings. The major elements found in the interface area were aluminum, silicon, zinc, and chlorine. The majority of the hard adherent coating was found to be zinc oxide and a zinc chloride compound with some metallic zinc.