In 1987, a major effort to understand the effects of resizing treatments on naturally aged papers was begun at The Johns Hopkins University (Baltimore, USA). This article presents a visual dictionary of characteristic changes in paper surface morphology caused by different resizing agents (gelatine, Klucel G, methyl-cellulose, parylene, starch, parchment size). In general, individual resizing agents are associated with typical surface structures that are related to the rheological characteristics of the resizing solutions, the surface topography of the treated papers, and the original fiber and size content of the papers before treatment.