Slag inclusions present as missing areas (a mix of round, irregular or angular shaped craters or cavities) of metal in the casting or black, crusty particles sitting on the metal surface. This defect indicates a presence of liquid and solid slag inclusions; which are being carried into the shell by the metal.

The causes of this defect are evident in the metal and other portions of the process. To cure these causes, R&R recommends taking the following actions.