Not sure you like butter? The buttercup knows, casting a yellow spot on the chin of all butter-lovers, or so says childhood lore. Now researchers have illuminated the flower's ability to ferret out butter fans. Armed with microscopes and a spectrometer, which analyzes the wavelengths of reflected light, the team found that the petals of the buttercup (Ranunculus repens) have a transparent outer coating that reflects light, enhancing the blossom's shine. Beneath that coating, a layer of yellow pigment rests on a layer of air. Light passes through the pigment, bounces off the air and zips back through the pigment before reaching a viewer's eye, according to a study published online today in The Journal of the Royal Society Interface. The light's double passage through the pigment creates an intense yellow. The buttercup is so glossy that if held at the right angle, it reflects sunlight onto human skin, like a mirror. Thanks to its pigment, the flower reflects yellow light—even onto the chins of butter-haters.
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