Microscopic analysis of West Mexican ceramics (dating between ) in the collection of the Department of Arts of Africa, Oceania and the Americas at the Metropolitan Museum of Art has established five different morphological types of manganese dioxide (MnO2) accretions. The accretions result mostly from a combination of bacterial and weathering activity in post-depositional contexts. Optical microscopy, scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDS) and x-ray fluorescence (XRF) were successful; whereas microchemical spot tests, x-ray diffraction (XRD) and Raman spectroscopy proved inconclusive in the identification and differentiation of the five morphologies. Accretion morphology and substrate characteristics, together, suggest scenarios for the mechanism of formation and offer a qualitative tool for authentication. Accretions were documented using photomicrography, categorized based on empirical observation; sampled and analyzed using SEM-EDS and ND-XRF.