Fig. 6. OM image of a 2 mm thick as-cast step part showing an inhomogeneous skin layer, where the skin appears to be migrating through the thickness of the casting and ending abruptly, as indicated by the red dashed lines. (Adapted with permission from Dalai et al. [19]). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)