This type of inspection consists in applying a colour contrast or fluorescent liquid (penetrant) on the surface to be inspected.

The liquid is drawn into the existing surface flaws (cracks, porosity, pinholes).

Excess penetrant is removed by cleaning action. The surface is coated with a thin layer of developer which acts as a ‘’blotter’’, lifts the penetrant out from the flaws and gives a coloured stain.

There are two procedures:

The method applies to many kinds of compact and nonporous materials (metallic materials, plastic, composites…) of any geometry and size and allows the test of the whole testpiece surface.