Which of the following can cause false indications during penetrant testing?

Lint or dirt can indeed cause false indications during penetrant testing because these contaminants might obscure or mimic cracks or defects on the surface of the material being inspected. The penetrant testing process relies heavily on clean surfaces to ensure that the penetrant can enter any discontinuities. When debris is present, it can interfere with the visibility and accuracy of the test results, leading inspectors to either miss real defects or see false positives.

Heat applied to the sample impacts the physical properties of the penetrant or the material but does not directly contribute to false indications in the same way that dirt does. Overexposure to penetrant can cause bleeding, which can affect the clarity of indications but typically does not create false indications linked to surface contamination. Excessive air pressure is more likely to affect the application method and not directly lead to false indications related to surface contaminants. By maintaining a clean testing environment, the reliability and validity of penetrant testing can be ensured.