The clouds are brighter at night
Black-and-white negative pictures turning into positive image thanks to chemical emulsion on multi-graded paper makes my conception of image twisting. Now a white paper turns into black, if you expose too long. That is the whole liberty of printing in a dark room : playing with the exposures and other measures will let you decide of your final output. The clouds can be brighter as the clear blue sky, if you want it.
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