Why Would Famous Artists Mix Oil and Tempera Paints?

The 15th century represents an important transition in art history, as oil paints gradually replaced egg-based tempera paints as the painting medium of choice. During the transition period, artists sometimes mixed materials, combining oils with tempera paint to create a blend known as tempera grassa. Reporting in ACS Applied Polymer Materials, researchers explored the effects of adding oil to tempera paint to better understand how various paint formulas would affect the appearance of finished works. Surprisingly, they found that adding oils to tempera paint does not slow its drying time, as had long been assumed. But artists may have had other reasons for creating the mixture, as the researchers discovered.