In penetrant testing, what is the purpose of applying a developer?

• A. To clean the surface
• B. To provide a contrasting background to reveal indications
• C. To emulsify penetrant
• D. To seal the surface

Answer: (B)

The purpose of applying a developer is to create a contrasting background that makes any indications from penetrant visible. After the penetrant has seeped into surface flaws and the surface has been cleaned of excess penetrant, the developer is applied. It acts like a blotter and draws penetrant out of flaws by capillary action, concentrating it at the surface so the flaw becomes more evident. The light or white background the developer provides enhances contrast with the colored or fluorescent penetrant, allowing you to see the defect shape, size, and location clearly. This visibility is why the developer is essential in LPI. It isn’t used for cleaning, emulsifying, or sealing the surface.