Why Mondays are Blue

Ever wonder why Mondays are called “blue”? Some blame post-weekend gloom, others point to hangovers. But the phrase has a more literal origin in 19th-century washhouses. Washday almost always fell on Monday, and the final rinse often shimmered faintly sky-blue. Housewives were bluing the clothes, adding a drop of dye that canceled yellowing and made whites gleam.

Long before electricity, people battled dingy linens with chemistry from the corner shop. A splash of blue in the rinse was enough to brighten their whites. The science is simple: because blue sits opposite yellow on the color wheel, a hint of blue neutralizes the yellowing from sun, soap, and hard water, so the eye perceives the result as a cleaner, brighter white.

The practice evolved with the times. In 1907, Persil launched as a “self-activating” powder, and by mid-century detergent makers had gone beyond bluing to optical brighteners: molecules that absorb invisible UV light and re-emit a faint blue glow. Machines caught up too: from bolt-down automatics to today’s whisper-quiet inverters, washers standardized the ritual, but never retired the trick. Peek at modern “whitening” detergents and you’ll still spot a blue-tinged promise on the label.

Although laundry is far easier today, Blue Monday lingered as a symbol of other modern dramas. Next time your washer beeps and a basket of “bright whites” lands on the sofa, remember: this used to consume an entire day.

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