The field of rheology is vast and often overlooked, even in closely related areas such as additive manufacturing through the Material Extrusion technique of Direct Ink Writing (DIW or Robocasting). Hence, this study provides a comprehensive characterization of pastes consisting of alumina-toughened zirconia (ATZ) powder, a deflocculant, a binder, deionized water and, in some cases, carbon nanofibers (CNFs). The rheological behavior and fundamental properties of these pastes were determined and printability tests were conducted. The results were compared to established printability criteria/parameters outlined in existing literature (ф, K and FTI). These criteria were found to be suitable for assessing printability, although they presented some limitations in predicting some unprintable pastes. Furthermore, a new criterion based on the recovery rate was introduced, with the potential to predict printability with a single test. Overall, these findings shed light on the rheology field which is increasingly recognized as important by the research community and whose thorough understanding can unlock the potential to create more intricate pastes capable of constructing more elaborate structures.