When does dwell time begin for dry developers?

• A. Begins after cleaning
• B. During drying
• C. Begins at application
• D. After development completes

Answer: (C)

Dwell time is the exposure period during which penetrant has to enter a defect after it is applied. For dry developers, this period begins as soon as the penetrant is applied to the surface, not later during drying or after applying the developer. The process then continues with removing excess penetrant and applying the dry developer, followed by development to reveal indications.

So the reason this is the best answer is that the penetrant needs contact time with flaws right from application, and starting the dwell timer at that moment ensures consistent penetration regardless of the subsequent steps. The other options don’t fit because cleaning, drying, and development steps occur after penetrant application, and they do not define the start of the penetrant dwell period.