A detailed X‐ray diffraction study has been made of the reactions which occur at the enamel‐steel interface during the firing of a titania enamel directly on steel. The following crystalline compounds have been found near the interface under various conditions: (1) Fe3O4, (2) FeO, (3) FeTiO3, (4) anatase, (5) rutile, (6) nickel‐iron alloy, and (7) an unidentified compound designated “unknown X.” The Fe3O4and FeO make up the initial oxide layer which forms on the steel before the enamel fuses. The FeTiO3is formed by reaction between dissolving FeO and dissolved TiO2in the enamel. Anatase is the primary opacifying crystal which precipitates because of supersaturation of the frit, but it is drawn back into solution as FeTiO3precipitates. Rutile is a secondary opacifier which forms relatively slowly and apparently causes the re‐solution of the FeTiO3. The nickel‐iron alloy appears only as a trace and probably comes from reaction between FeO and a small amount of nickel oxide formed on the nickel‐flashed samples. The most important observable effect of nickel pickling is its drastic reduction of the amount of oxide initially formed. Increasing the firing temperature increases the rates of all the reactions, but most particularly the precipitation of rutile and the disappearance of FeTiO3. The adherence development of this enamel on Ti‐Namel steel is dependent to a great extent on the weight of nickel deposit and the firing temperature and time. The theory that adherence depends on the presence of an oxidizing agent in the enamel adjacent to the steel has been applied to this system, and a correlation has been obtained on the assumption that dissolved TiO2is the adherence‐promoting oxidizing agent. The titania enamel does not develop adherence on a regular enameling iron under conditions where good adherence is developed on Ti‐Namel steel, although the reactions in the enamel are essentially the same. This may result from observed differences in crystal orientation or texture, behavior of the nickel deposit, o