What is the preferred thickness of developer for revealing very fine cracks?

The preferred thickness of developer for revealing very fine cracks is a thin layer. This is because a thin application allows for better penetration into the cracks due to the reduced surface tension and increases the likelihood that the developer will seep into these small openings. A thin layer ensures that the developer can form a clear contrast against the surface, making subtle defects more visible.

When using a thicker layer of developer, it can create a masking effect, obscuring fine details and potentially leading to misinterpretations of the results. Additionally, a thick layer tends to take longer to dry, which can further complicate the detection of fine cracks. Therefore, a thin layer is more effective for the purpose of revealing very fine cracks.