Ash or dust inclusions present as missing areas (small, round, irregular or angular craters or cavities) of metal in the casting. This defect indicates that there may be ash particles in the mold (on the top side of parts); while on the bottom side of parts, it may be dust particles in the mold (top and bottom are relative to the location of the part while they are treed up for casting). These particles, present in the mold cavity or the metal, prevent the casting from fully filling the shell.

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