What is the main purpose of using a developer on a test specimen?

The primary role of a developer in the context of non-destructive testing, specifically when examining test specimens for surface flaws or discontinuities, is to absorb penetrant from these discontinuities. In penetrant testing, a dye or liquid penetrant is applied to the surface of the specimen, and it seeps into any surface-breaking defects present. After allowing the penetrant to dwell, a developer is then applied, which draws the penetrant out of the defects by capillary action. This process makes the defects visible against the background of the developer, allowing for effective inspection and evaluation of the specimen's integrity.

This functionality is essential in ensuring that any discontinuities are easily detectable, thus enhancing the reliability of the testing method used for materials and components.