What is a potential problem with retesting a test specimen that has been previously tested using liquid penetrant?

The challenge associated with retesting a test specimen that has been previously examined using liquid penetrant lies primarily in the issue of dried penetrant residue. When a penetrant is applied to a part, it seeps into surface-breaking defects and is subsequently removed in a cleaning process. However, if the specimen is retested, any leftover dried penetrant residue may not dissolve easily during the cleaning process prior to reapplication of the penetrant. This residue can interfere with the effectiveness of the new penetrant application, potentially masking flaws or leading to inaccurate testing results.

The concern about other potential issues like new discoloration, damage to parts, or contamination points to different aspects of the testing process, but they do not directly affect the core concern regarding the efficacy of the penetrant testing related to residue. Therefore, the dried penetrant residue not dissolving readily presents a significant problem for accurate retesting.