Which test uses black light to detect contamination on surfaces?

The correct answer is the hydrocarbon test, which employs a black light to identify contamination on surfaces. When surfaces have been contaminated with hydrocarbons—such as oil, grease, or other coatings—they typically fluoresce under ultraviolet black light. This detection method is advantageous because it allows inspectors to spot contaminants that may not be visible under normal lighting conditions, ensuring that the surface is adequately prepared for painting or coating.

In contrast, the other tests listed do not utilize black light for detection. The moisture test typically uses probes or other electronic devices to measure moisture levels on surfaces. The adhesion test assesses how well a coating adheres to the substrate, often through physical methods like tape pulls rather than any light-based detection. The salt test is designed to measure the presence of salt contaminants, usually using a quantified solution or other wet methods rather than luminescence. Collectively, these distinctions highlight the unique role of the hydrocarbon test in identifying surface contamination.