A red image against a white background is typically observed with which type of penetrants?

The observation of a red image against a white background is characteristic of visible dye penetrants, which are specifically designed for non-destructive testing applications. These penetrants contain a colored dye, often red, that provides high contrast against light backgrounds, making it easier for inspectors to identify defects in the materials being tested.

Visible dye penetrants are applied to the surface of materials and then allowed to seep into any cracks or voids. After a specified dwell time, excess penetrant is removed, and a developer is applied to draw out the penetrant from the flaws, resulting in a clear and vivid red indication against the white background of the developer. This color contrast is essential for effectively diagnosing and visually inspecting surface defects.

Fluorescent penetrants, in contrast, would typically show a bright green or yellow glow under ultraviolet light, not a red image. Solvent-based and oil-based penetrants may be less common or have different visual characteristics that do not align with the specific red image against a white background.