Why once-gold ceilings in Spain’s Alhambra palace have purple stains

Spain's Alhambra palace is considered a pinnacle of medieval Islamic architecture. Scientists now know why some of its intricate gold decorations turned purple.

Corrosion processes formed gold nanospheres of the right size for violet

Once upon a time, Spain’s hilltop Alhambra palace glittered with gold. Over the centuries, though, the Islamic citadel’s ornate, gilded structures on its ceilings and elsewhere fell into disrepair, with curious purple splotches marring them. The stains’ origins were a mystery. But scientists say they now understand the chemistry behind the purple tinge.

Analyses reveal that as the gilding decayed, it formed gold spheres invisible to the naked eye that are responsible for the purple color, the researchers report online September 9 in Science Advances. The finding may have implications for understanding how other art and architecture degrades with time.


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