Warning, this post may be controversial:
I have a personal observation regarding Iron X and all like products.
I have Iron X but don't necessarily buy into the theory.
So a chemical reaction takes place between the contaminant and the Iron X or said like product and it bleeds purple because of the chemical. But based upon my use of the product it does not completely dissolve the contaminant in one application to where it's totally removed. I have experimented with this recently with one of our newer cars. I applied it and let it soak in for 15 minutes, rinsed it off and reapplied it and it was still bleeding purple.
As detailers the next step is to use an aggressive method like clay or "nanoskin" to remove the contaminant. So really what does the chemical reaction that takes place do other than identify that contaminants are present on the paint? Doesn't the .01 cent baggie test pretty much tell us that the paint has contaminants and to clay or skin it?
So for me, personally I'll not be investing in any more spray chemicals that turn purple, I'll just use the baggie test and go from there.
PS I work for a national distributor of cleaning supplies and equipment, ie: carpet extractors, floor scrubbers etc and THD bought us a year ago. Our core business is hospitals, hospitality, education and my personal expertise is food processing and packaging systems. I've been through a few manufacturers training schools in my time. 3M, SC Johnson, Spartan Chemicals to name a few. Cleaning and sanitizing afood processing plant is a little more sophiticated than deocontaminating paint. You don't get sick from licking your cars paint LOL.
