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When I was a kid, I knew that if you picked that little bug out of the white stuff on a prickly pear, and squished it in your fingers, it made a red stain. I probably thought it was blood. Nope.

That little bug is a "Cochineal bug", one of several species related to a scale insect, Dactylopius coccus. Aztecs and Mayas used it to dye cloth, and it's still used to produce the dye carmine. It changes color in basic and acidic solutions, so we experimented with the effect of acidity on the dye's color.



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