Pinholes or Gas
Bubble-shape cavities located on top side of parts when the tree is in casting position
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
Causes of this defect are evident in the other portion of the process; to cure, R&R recommends taking the following actions:
Burnout cycle is too short, burnout temperature is too low or there is a lack of oxygen in the burnout oven.
Any of these can cause incomplete pattern burnout.