Heat boiling off chemicals that prevent separating and gelling may result in what?

• A. Increased adhesion to the surface
• B. More stable gel formation
• C. Faster removal of penetrant
• D. Removal of penetrant from the surface flow

Answer: (D)

The main idea is how heat affects the stability of the penetrant film on the surface. Penetrants include additives that keep the liquid in a uniform, low-viscosity film so it can flow and cover tiny surface features without separating or gelling. If heat boils away those additives, the penetrant loses that stability. It can start to separate or form gels, making the film breakup and lose continuous flow across the surface. As a result, portions of the penetrant can be removed from the surface flow—carried away by drying or cleaning actions—leaving less penetrant on the surface to reveal indications.