Street art is increasingly recognized as part of today’s cultural heritage, yet it remains highly vulnerable to time and weather. Not all pigments used in murals have the same durability. A team from the University of Pisa, the National Research Council of Italy (CNR), and the University of Perugia has investigated why some colors deteriorate more quickly than others. Their findings were recently published in Proceedings of the National Academy of Sciences (PNAS).

The researchers focused on Musica Popolare (2017), a 400-square-meter mural in Milan’s Ortica district. Depicting icons of Milanese music and culture, the work has become a symbolic landmark for the city. To study it, the team developed an innovative method combining portable spectroscopic analysis, hyperspectral imaging, and drone-based multispectral surveys, along with laboratory chemical tests on micro-samples.

The results show that red tones are particularly fragile: they fade quickly and produce degradation compounds. Purple and yellow pigments are more stable, while black and gray retain their intensity for much longer. The choice of binder also plays a crucial role: acrylic and styrene resins tend to lose brilliance and powder off, especially when titanium dioxide is present, which accelerates the deterioration process.