Although crude, the technique had all the stages of a modern penetrate NDT procedure:

Application of a liquid which would penetrate surface cracks.

The oil and chalk technique was superseded by magnetic particle inspection (M.P.I). Although a more sensitive non-destructive test, M.P.I can only be used on Ferro magnetic materials with the increasing use of aluminum and stainless steel, there was still a need for a sample and effective NDT methods for detection of surface breaking discontinuities.