Freckles are a detrimental grain defect formed during directional and single crystal solidification of superalloy components leading to a high rejection rate. Based on the experimental and theoretical studies over the past forty years, the occurrence of freckles is generally believed to be mainly dependent on the alloy chemistry and process parameters, while the geometrical factor of castings was hardly taken into account. In the present work, a series of superalloy castings with complex geometry were directionally solidified in a production-scale Bridgman furnace. Some new features of freckle appearance have been observed, indicating new aspects of freckle formation. The freckles are preferably formed on the edges instead of on the plane surfaces of the castings. Correspondingly, freckles were found exclusively on the casting surface having positive curvature, whereas no freckles formed on the surface with negative one. The casting portions having inward sloping surfaces are very freckle prone, while those with outward sloping surfaces are absolutely freckle free. Therefore, as an independent factor the geometrical feature of the castings can more effectively affect the freckle formation than the local thermal conditions. It was also observed that freckles could occur not only on the external surfaces, but also inside the castings where a core was inserted, because both the shell and the core wall can provide very high permeability for freckling convection in the mushy zone. Based on this wall effect, all the important phenomena observed in the present work, such as the edge effect, the step effect, the sloping effect and the curvature effect on freckle formation in complex castings of superalloys, can be reasonably explained.