Non-destructive penetrant testing (PT symbol) is a technique based on the principle of capillarity. It is therefore limited to open surface defects and opening (cracks, cracks, porosity, sting...) but is very interesting inasmuch as it is a general control method, in contrast to ultrasonic or eddy current remaining local control methods.

PT comprises applying to the area to be controlled, an impregnating liquid, the penetrant which contains dyes for light in consideration of the day or in ultraviolet light (UV- A). After several steps (impregnation time, elimination of excess penetrant, application of a developer), the penetrating trapped by capillarity in the "sweated" defect and leaves a visible indication to the naked eye. If this method does not measure either the width or depth discontinuities, it gives a clear indication of their length and their importance. It can identify defects and to deduce their origin and evolution of risks.

This method is applicable to a wide variety of materials as they are compact and non-porous : all metal materials they are ferromagnetic or non-ferromagnetic, some plastic, some composites, ceramics...

The advantage therefore bleed the magnetic is not limited to ferromagnetic materials. However, its limitation is the requirement to control extremely clean rooms since the defects must be absolutely open surface.