What distinguishes Type I penetrants from Type II penetrants?

Type I penetrants are distinguished by their fluorescent properties, which allow for detection under ultraviolet (UV) light. This feature is particularly advantageous in identifying very fine defects, as the fluorescent penetrant will glow brightly against a dark background when exposed to UV light, making it easier to visualize cracks and surface defects.

Type II penetrants, on the other hand, are primarily designed to be visible dyes. These penetrants can be seen in normal lighting without the need for UV light, which makes them suitable for applications where fluorescent inspection is either not possible or not necessary. Visible dye penetrants are commonly used for general-purpose inspection methods where fluorescent equipment is not available.

The distinction between the two types, therefore, lies significantly in their method of detection — one utilizes fluorescence, while the other relies on visible coloration under standard light.