Which penetrant type relies on visible light for indication and is used under ordinary shop lighting?

• A. Visible color contrast penetrants
• B. Fluorescent penetrants
• C. Magnetic-particle penetrants
• D. Ultrasonic penetrating methods

Answer: (A)

Visible color contrast penetrants use a dye that creates a color you can see under ordinary room lighting. After applying the penetrant, removing the excess, and applying developer, any defects draw the dye to the surface, producing a colored indication that’s visible to the naked eye without special lighting. This makes the method simple and cost-effective for everyday shop use.

Fluorescent penetrants, by contrast, require ultraviolet light to make the indicator glow, usually in a darkened area with proper UV equipment. Magnetic-particle methods involve magnetic fields and iron particles, not a visible dye under normal light. Ultrasonic methods aren’t penetrants at all—they use sound waves to detect flaws.