Why does an image you draw on a window appear again and again when the window has condensation? Why does it not condense over tge drawing?

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Why does an image you draw on a window appear again and again when the window has condensation? Why does it not condense over tge drawing?

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Your skin have a layer of fat on it. When you put your finger on the window you leave a thin layer of grease on the glass. It is thin enough that you do not see it normally. However when the window gets colder then the dew point the thin layer of grease provides a tiny bit of isolation so it condenses on the other parts of the window first. Since the condensation process reduces the humidity and therefore lowers the dew point it may never condense on the part that is greased up by your fingers.