A technique has been developed by which a microcrack may be propagated in a controlled manner through a small slab, with simultaneous microscopic observation of the path of the crack and the force changes occurring during propagation. For studies of grain boundaries effects, specimens require grain sizes at least as large as specimen thickness (∼50 &mgr;) in order to define the effect of a single boundary on the crack path. Crack behavior may be observed by means of optical microscopy and would be suitable for scanning or transmission electron microscopy. Application of the technique to ceramic bicrystals indicates strong crack pinning points within the individual crystals as well as at the grain boundaries. In polycrystalline materials, these pinning points result in a start‐stop process which is repeated numerous times.