Pinholes or gas present as bubble-shape cavities located on top side of parts when the tree is in casting position. This defect indicates that there was unburned wax pattern residue (soot or ash) in the shell; when molten metal was poured into the shell cavity and came into contact with the ash residue, gas was formed and trapped in the mold. 

 

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