A Visible Dye Penetrant system allows a quick and easy check, without any special UltraViolet (blacklight) equipment
. It is perfect for quick checks.
The Fluorescent UV system is more sensitive, finding smaller cracks than the visible system, but it requires the use of a UltraViolet light source.
Dry or Wet Magnetic Particle Testing is an excellent testing method for ferromagnetic materials.
What Veda said. ✓