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I noticed these patterns in the condensation on the inner surface of my car's windshield when I turned on the defroster. Usually when I see lines like these on condensation I assume it's because of snails/slugs altering the surface chemistry of the glass, but in this case 1) the lines seem too straight to be from a snail, 2) the angles are too sharp/consistent, and 3) there aren't any snails in my car. They also don't seem to be ordered enough to be artefacts from the manufacturing process (it's a new car). Anyone have any ideas?

Condensation Pattern

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  • $\begingroup$ My first thoughts were: scratches, cracks, or spider webs. The topology of the lines makes spider webs seem unlikely. Cracks in a new car's windshield would be unlikely, and the topology seems wrong. I would drag a razor blade or fingernail across one of the lines to see if I could feel a scratch. One more possibility: the windshield may have been wrapped in something that left those lines, in the form of contamination on the surface. You could try scrubbing a place on one of the lines, using acetone; then see if the mark shows up next time there's condensation inside your windshield. $\endgroup$ – S. McGrew Nov 5 '18 at 14:25
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Condensation patterns like this are commonly caused by tiny amounts of dirt or chemical residues on the glass surface that locally alter the condensation kinetics. I do not know what caused this particular pattern but try cleaning the window off with Windex/ammonia cleaner and a clean paper towel and see if the pattern persists.

By the way, people who work in cleanrooms with silicon wafers used to exhale on a wafer to see if it was properly cleaned. If it wasn't, swirly patterns of condensation would show up indicating contamination from the previous processing step.

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  • $\begingroup$ Please explain the downvote so I do not err again. $\endgroup$ – niels nielsen Nov 6 '18 at 1:02

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