it's a flawed method of confirming whether an LSP is present or not. Because water beads on clean surfaces, ie condensation on the side of your cup, most windows or glass surfaces produce beading effects as well. And water beads on oils and waxes as well. Can the effects on beading by a wax or polish compared to an absolutely clean surface actually be determined by the naked eye? I would say probably not. However, IPA is pretty amazing at cleaning oils. Have you ever used IPA to clean a water pipe that was caked with resin? I'm certain the resin along the inside of a water pipe is much stickier and greasier than the oils in a polish or a wax you apply on your car. I am 100% confident that there is no residue left after a thorough IPA wipedown. In fact, I wouldn't use anything other than IPA for 2 reasons: 1. how well it cleans my bong. 2. it is way cheaper than cleaners made for cleaning polish residue. Those are gimmicks that companies created to simply make money off detailers.
I have to stop you because IPA is not the cleaner you believe it is. I am not coming at you from a detailing perspective or as someone who has a few cleaning solvent kicking about - we manufacture hundreds of tonnes of cleaning products in a year. Isopropanol is a moderately polar solvent which is useful in a great many situations - that is not in doubt. However, it is simply not even close to the most potent solvent out there. Heck, you can use it on household paint and you would struggle to do a lot of damage. Contrast that to non-polar and aromatic solvents and it is a weakling compared to many.
For fact, we don't use IPA as a carrier for many products because it will not dissolve them. Wax does not easily dissolve in it (and even then, in small proportions), many polymers and resins will not dissolve, silicones are troublesome. You should recognise that each of these things, common in car care, are highly non-polar in character. You should also not be surprised at what we do use as carriers - non-polar solvents (think of mineral spirits as one of the
least potent of this class).
Think even on automotive - if IPA was as potent as you imply, why do we have to resort to non-polar solvents (typically xylene and toluene) for removal of tar? IPA simple does not touch the sorts of tar deposits common in the UK. The reason is simply, tar is highly non-polar and IPA is not. Like dissolves like is a good general rule.
As for the validity of the method, I will have to disagree. As I stated, even if I was to discard everything else, I can physically
see that the sealants are still there. IPA does
not remove them (nor does wash up liquid, APC, TFR and often even heavy non-polar solvents, for that matter). The hydrophobicity of the surface is far too high to be mistaken. I was not wishing to go to this depth but contact angles for water on clean paint are rarely greater than 75 degrees - yes, slightly hydrophobic and it could give beads and sheets. The surface I have presented have contact angles in excess of 100 degree - there is absolutely no mistaking that difference, even by eye.