Thanks Franc. There are two types of Magnaflux testing: magnetic particle and dye penetrant. Magnetic particle requires special equipment which far exceeds my budget. Dye penetrant is what you see up there. It's a three step process all of it coming out of spray cans. The process is simple. Clean the area to test, spray on the penetrant then wait a few minutes before wiping away the excess. Spray on the developer and there you have it. Cracks show as red lines against the white. It's a simple but very effective way to find defects otherwise invisible.
Magnaflux spot check website Hank
