Which characteristic is essential for a good penetrant?

A good penetrant must be inert with respect to the materials being tested because this ensures that it does not react chemically with the substrate or alter its properties during the testing process. If the penetrant were to interact chemically with the material, it could introduce new flaws or affect the integrity of the part being inspected. Therefore, maintaining the original condition of the material is critical to obtaining accurate results during Liquid Penetrant Testing.

While characteristics like being colored for visibility can aid in the detection process, and non-flammability is often a desirable safety feature, these factors do not fundamentally impact the effectiveness of the penetrant's performance with respect to the integrity of the materials being tested. High viscosity may affect the flow and penetration of the dye into a crack, but it does not determine the overall quality and suitability of the penetrant for reliable inspections.