Why once-gold ceilings in Spain’s Alhambra palace have purple stains
Corrosion processes formed gold nanospheres of the right size for violet
![landscape photo of the Alhambra palace](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2022/09/090822_CD_alhambra_feat.jpg?fit=1030%2C580&ssl=1)
Spain's Alhambra palace is considered a pinnacle of medieval Islamic architecture. Scientists now know why some of its intricate gold decorations turned purple.
Jebulon/Wikimedia Commons (CC0 1.0)