Surface Methods – Liquid Penetrant Inspection (LPI) Exam 1 Practice

Visible dye colors are available in which color most commonly used because of its high contrast with developer on metal surfaces?

Red is most commonly used because of its high contrast with developer on a metal surface

Visible dye penetrant inspection relies on color contrast between the penetrant and the developer. The developer is typically white, so the penetrant color must stand out clearly against a light background. Red provides the strongest and most consistent contrast against white, making indications easy to see on metal surfaces under standard lighting. While other colors can be used in certain situations, they don’t offer the same universal visibility, which is why red is the most commonly used color.

Orange is more visible on polished steel

Purple offers higher contrast than red

Green provides better contrast in dim light