This solution stains the sigma phase of;

• Iron +(12–30%)Chromium +(<6%)Nickel (400 Series steels)
• Iron +(15–30%)Chromium +(6–40%)Nickel +(<5 %)other elements (300 Series)
• Iron +(16–25%)Chromium +(3–6%)Nickel +(5–10%)Mn (200 series)

It also delineates sigma phase and welds of dissimilar metals in Series 300 & Series 200 steels

Used to reveal the general structure of Nickel-Chromium alloys.

Solution 3 is also used for Molybdenum, Rhenium & Tungsten base metals.