Penetrant materials based of light requirement classified in two types.
- Type 1 – Fluorescent Penetrants
- Type 2 – Visible Penetrants
Fluorescent penetrants contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation. Fluorescent penetrant systems are more sensitive than visible penetrant systems because the eye is drawn to the glow of the fluorescing indication.
Visible penetrants contain a red dye that provides high contrast against the white developer background. However, visible penetrants do not require a darkened area and an ultraviolet light in order to make an inspection. Visible penetrants are also less vulnerable to contamination from things such as cleaning fluid that can significantly reduce the strength of a fluorescent indication.