Casting is a process of pouring a liquid, typically metal or plastic, into a mold to produce a solid part. That’s the theory, but in fact “solid” parts often contain voids or inclusions, which may or may not impact the performance of the finished part. Porosity can be bad, meaning that the resulting part will not perform as required due to reduced strength or open pores left after final machining. It can be acceptable, meaning either that the void will be removed by secondary processes such as machining or that it is internal and of a size and shape that will not affect performance. Or, the porosity can be desirable when it is created intentionally to reduce weight. Even then the size of pores can be critical. The challenge is differentiating bad porosity from acceptable porosity or desired porosity, and diverting bad parts before either spending additional production time on them or sending a sub-standard part to market.