Liquid / Dry Penetration Testing is used to check for surface cracks/flaws of a component. There are 2 types of color contrast techniques which are visible & Fluorescent.
Test object are coated with visible or Fluorescent dye solution. Excess dye is then removed from surface and a Developer is than applied onto it. The developer acts as a blotter drawing trapped penetration out of imperfection open to the surface. Any imperfection/cracks are seen visibly by the “Bleed out”.
Advantages
Liquid Penetration Testing offers an unaided visual inspection which makes defects easier to see for the inspector.
Disadvantages
The test surface must be clean and smooth, any paint are to be removed.