If Painting for the Ages, Beware of Unstable Minerals
To see chemical transformations of minerals in action, look to art! Certain minerals have long been ground up and used as paint pigments. But those same minerals are known to degrade over time. Bright blue azurite is particularly notorious. In damp conditions, it oxidizes to green malachite. us, skies and seas painted for audiences long ago have taken on a decidedly dierent hue for audiences today.
Now, another mineral has proven problematic. Writing in the journal Science Advances, Nouchka De Keyser (Rijksmuseum, Amsterdam) and colleagues have shown how a rose in a 17th-century still-life painting has likely morphed from yellow to brown. It seems to have originated as orpiment, an arsenic sulde. Light caused the orpiment to change to arsenolite, which then reacted with lead white paint, producing mimetite and schultenite. us, the bright yellow rose of old has declined with age to a sad and wilted brown.
If painting for the ages, take a mineralogy course and seek pigments composed of elements that won’t be aected by oxygen, water, or other minerals over time.