When using a wet developer, what is the recommended thickness for optimal detection of very fine cracks?

Using a wet developer in liquid penetrant testing is crucial for maximizing the visibility of surface defects like very fine cracks. The recommended thickness of a wet developer should be kept thin. A thinner layer allows the penetrant that has entered the cracks to be drawn out more effectively, making the defects more apparent when viewed under UV light or white light. This is essential for detecting fine defects since a thick layer may actually obscure them, potentially leading to false results or undetected issues.

A thin application also promotes quicker drying and reduces the chance of excessive background fluorescence, allowing for easier interpretation of the test results. This is why the best practice is to apply a light, even coat when using a wet developer in order to enhance the visibility of any defects present.