When does dwell time begin for wet aqueous developers?

• A. Begins immediately after application.
• B. Begins as soon as the developer is dry.
• C. Begins after a pre rinse.
• D. Begins after the penetrant is wiped off.

Answer: (A)

Dwell time is the period during which penetrant remains in contact with the part to enter any surface-breaking defects after application. For wet aqueous developers, this time starts as soon as the penetrant is applied to the surface and ends when you remove the excess penetrant. The developer application comes after this interval, not during it, because the purpose of dwell is to allow penetrant to seep into flaws before any cleaning or developer action. If dwell began after a pre rinse, after drying, or after wiping off, you’d be delaying the diffusion window and could miss indications. So the dwell time begins immediately after the penetrant is applied.