X-ray photoelectron spectroscopy is used for studying, both qualitatively and quantitatively, the chemistry of steel/enamel interfaces. Experimental evidence is presented that high adherence is achieved when the interface consists of a single, fully reacted iron silicate plase. Conversely, poor adherence is characterized by an iron silicate phase plus some unreacted FeO. The presence of this latter phase derives from the fact that oxide formation by the steel is unbalanced by oxide dissolution through glass attack, whereas there is no evidence for FeO diffusion into enamel. Our results lend experimental support to the chemical theories of adherence at steel/enamel interfaces.