{"id":69534,"date":"2026-11-14T04:35:28","date_gmt":"2026-11-13T19:35:28","guid":{"rendered":"https:\/\/phys-edu.net\/wp\/?p=69534"},"modified":"2026-11-14T04:35:28","modified_gmt":"2026-11-13T19:35:28","slug":"red-paper-turns-blue-in-a-flash-a-hair-dryer-reveals-the-secret-of-invisible-moisture","status":"publish","type":"post","link":"https:\/\/phys-edu.net\/wp\/?p=69534&lang=en","title":{"rendered":"Red Paper Turns Blue in a Flash! A Hair Dryer Reveals the Secret of \u201cInvisible Moisture\u201d"},"content":{"rendered":"

Ken Kuwako, Science Trainer, here. Every day is an experiment!<\/strong><\/span><\/p>\n

Ever noticed that the cobalt chloride paper sitting on a shelf in the lab has quietly turned pink or pale and washed out? Here’s the fun part: just hit it with a hair dryer, and it flips to a vivid blue in no time. And you can repeat the trick as many times as you like. This is the story of a magical little paper that makes invisible humidity show up in color.<\/p>\n

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Cobalt chloride paper is a “water detector”<\/h3>\n

Cobalt chloride paper is a test paper used to check whether water is present. It turns from blue to pink (a reddish color) when it absorbs water, so in middle school science class it’s often used to confirm that water was produced when something is burned or heated.<\/p>\n

But the cobalt chloride paper sitting around in a lab, even if nobody has used it, has often soaked up moisture from the air and turned pink or pale. When the room is humid, the paper slowly takes in water from the air.<\/p>\n

Blast it with a hair dryer, and red turns to blue<\/h3>\n

So before the experiment, try blowing a hair dryer over the paper. A red piece turns blue almost instantly. That’s because the water in the paper has been driven off and the paper has dried out.<\/p>\n