Which property relates to how well penetrant spreads over a surface?

• A. Surface wetting
• B. Brightness
• C. UV stability
• D. Removability

Answer: (A)

Surface wetting describes how well a liquid spreads on a solid surface. In liquid penetrant inspection, good wetting means the penetrant can cover the surface evenly and flow into small surface-breaking flaws by capillary action. When the surface is clean and the penetrant formulation lowers surface tension (often with surfactants) and is at an appropriate temperature, it spreads smoothly, maximizing defect indication. If wetting is poor, the penetrant beads up and may not enter narrow cracks, increasing the chance of missing flaws. Other properties like brightness, UV stability, or removability don’t govern how the liquid spreads over the surface, so they’re not the correct focus.