The particular liquid penetrant, usually a red dye or a fluorescent dye using a black light, is applied to generally non-ferrous materials. It is also advantageous to use a low sulphur and halogen dye. The area to be tested must be clean.
Dye is applied for 30+ minutes, drawn into surface flaws by capillary action, then removed, leaving behind indications for further analysis.
After excess dye removal, a white developer is applied. A 15-minute wait reveals flaws as colored indications against the white background.
