The crack path up to its tip (point 3) can be located from a sharp contrast between the mechanically relaxed areas (yellowish tones) above the crack and those under tensile stress below it. A major crack is outlined by yellowish tones next to reddish ones, and secondary cracks branch on it and separate reddish areas from bluish ones. Between the notch and the crack tip, the points where crack pinning and stress accumulation was noted during the test (Fig. ) correspond to specific defects in the microstructure as observed from the surface. At point 1, the crack had to bypass a cluster of misaligned platelets, resulting in a diverted trajectory and stress contrast that contours both sides of the cluster. At point 2, branching is observed with a secondary crack seemingly appearing below a larger-than-average alumina platelet. At point 3, the crack is again pinned on a cluster of misoriented alumina platelets, and a very local stress concentration is observed before the experiment was stopped after 4 hours at a force of 114 N.