What happens if acid materials are not completely removed from a part before applying fluorescent penetrant?

When applying fluorescent penetrant for non-destructive testing, the presence of acid materials or other contaminants on the surface of the part can significantly hinder the process. If these contaminants are not completely removed, they can form a barrier that inhibits the penetrant from adequately penetrating the surface flaws, leading to a decrease in its effectiveness.

The penetrant relies on clean, unobstructed surfaces to fill cracks and other imperfections, so contaminants can interfere with this action. Specifically, acid materials may react with the penetrant or create an environment that reduces the visibility of the fluorescent indications under UV light. In essence, an unclean surface could conceal defects, impairing the purpose of using the penetrant in the first place. Thus, the presence of remaining contaminants directly correlates with a reduction in the fluorescence that should occur if the penetrant successfully highlights flaws.