Larry;
In one machine shop I worked in we had a Magna-Flux machine. This was used to detect surface cracks, it would not generally work on internal cracks. It would though pick up on extremely small ones which were virtually undetectable by eye. It worked by applying a liquid to the part which contained magnetic particles (the one we used was green in clor). The part was then held between the poles of an electric magnet. On even a micrscopic crack magnetic poles would be established on opposite sides which attracted the particles from the liquid. Larger cracks would be visible to the naked eye, but we always used this in conjunction with a Black Light, which would make those green lines stand out like a Neon Sign. I do not know what ingredients the liquid consisted of, but highly suspect you are totaly correct in your memory as to that being the cause of your Dads allergic reaction.
