Used mainly on stainless steels. It uses the principal of capillary action in order to draw a coloured dye into a crack type defect.
Once the dye has had time to enter the defect, usually between 10-20 minutes the surplus dye is removed by a clean lint free cloth and the remaining dye removed using a solvent moistened cloth.
A chalk like spray developer is applied to the object and any defects present are shown by the appearance of a red line appearing.
There are several methods of using liqiud penetrants including fluorescents.The most common method is red visible,solvent removable.