Sulfate Indicator Solution principally based on the precipitation of sulfate ion in such a manner as to form sulfate crystals of uniform size. The resultant turbidity is measured at a wavelength sensitive to turbidity on a photometer.
Hardness Titration Solution - II continues to be added till the displaces the indicator, complexing the remaining metal ions until all metal ions are bound to Hardness Titration Solution - II.
During the test formation of blue coloration indicates that the surface of the stainless steel does not yet pickled sufficiently . And if blue coloration does not appear which indicate surface has been satisfactorily pickled.