That's exactly what I've been experiencing too.Thieu wrote:I always use glass from photoframes. Last time I bought 40 plates from 2 different brands, 20 of each. Of the one brand, all plates cleaned well, nice hydrophylic surface, no beading at all. Of the other brand, about half the plates were not clean even after soaking overnight in pure bleach + double soap wash. My guess is that some batches of glass have impurities that make the surface hydrophobic, just like when treated with rainex. Plates I treated with rainex remain totally hydrophobic even with pure bleach treatment. The hydrophobic groups are chemically bonded to the surface and apparently very inert.
I suspect that those hydrophobic glass surfaces had been produced by silicone desposits (possibly from detergent/cleaning solutions containing silicone defoamers).