How blue is the sky?

“If I don’t have red, I use blue…”

Pablo Picasso

A cyanometer is an instrument for determining blueness, specifically of the sky. It was invented in 1760 by Horace-Benedict de Saussure to document the colour of the sky over the French Alps. He later completed his research with comparison measurements in South America. Basically, the clearer or higher the air, the bluer the atmosphere appears due to the Rayleigh scatter of nitrogen and oxygen molecules. De Saussure’s original cyanometer had 53 sections ranging from white to black. The blue pigment was Prussian Blue. This dye is an oxide of iron and cyanide. Prussian Blue is still a popular painting pigment, but also has a role as an antidote for heavy metal or radioactive poisoning. It still has a place on the WHO list of essential national medications. #goyoublues #letsmakelemonade

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