Traditional frescoes involve painting on wet plaster for a strong bond with the wall. But Leonardo da Vinci, always the experimenter, tried something different. He applied tempera (paint made with pigments mixed with egg yolk) on a dry plaster surface. Additionally, he prepared the wall with a special treatment to help the paint adhere. Working on a dry surface allowed da Vinci to take his time, add intricate details, and make changes to the painting as he went. This is evident in the incredible details and lifelike figures in The Last Supper. However, this unique approach led to the painting's slow decay over time.