To remove scales or scale deposits (mineral buildup) from something, usually a kettle, pipe, or other surface.
From 'de-' (remove) + 'scale' (crusty mineral deposits). Common household and industrial term that emerged as people dealt with limescale problems in water systems and appliances.
Hard water leaves behind limescale in your kettle because calcium and magnesium minerals don't dissolve—descaling products work by using acids that chemically convert the crusty deposits back into something water can dissolve.
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