The extensive literature on rubber-brass bonding provides a rather complex picture of the architecture of the bonding layers. In the present work, the morphology of cross-sections through the bonding layers perpendicular to the brass surface, seen in transmission electron microscopy (TEM), is used as a means of bonding layer classification. Previous experimental results with a simplified cure mixture (consisting of 1,4-polybutadiene, elemental sulfur, N,N-dicyclohexyl-2-benzothiazylsulfenamide, and, in some cases, zinc oxide) and brass foils are reconsidered. In nearly all cases, what we term a central layer is found. It consists of two sublayers with a different content of copper sulfides. Varying deposits of sulfides exist at the brass surface and also above the central layer in the direction of the rubber bulk. The various types of bonding layer with a different type of architecture are discussed in connection with previous results obtained by analytical electron microscopy (AEM) and bonding strength measurements.