New developments in the design of drop-on-demand printheads make it necessary to apply suitable testing techniques. The evaluation of the lifetime and the performance of prototypes is especially important for the case that advanced materials are incorporated.Here, our new thermal printhead based on diamond technology is evaluated. The outstanding thermal, mechanical and chemical properties of diamond allow the fabrication of more efficient devices, which offer a reduced complexity at the same time. The prospect of higher speed, cost reduction and longer lifetime are the reasons for an ongoing development based on this technology.This paper presents the results of lifetime tests of diamond thermal printheads together with the evaluation of their workability visualized by real time cinematography. Such a visualization by a high speed camera system coupled to an optical microscope reveals the system's performance since nonreproducible processes can be studied as well. This is important when one wants to search for reasons of device failures.