Magnetoscopy and penetrant testing are two types of non-destructive testing that are widely used in aeronautics.
The application of a fluorescent developer in the dark under UV (magnetic or not) makes it possible to identify the cracks or defects possibly present in the material and on its surface.
The controller is in charge of interpreting and validating the results, or issuing a "verification", or if necessary, establishing a Non-Compliance Report.