Which of the following art techniques requires the artist to paint on wet plaster?

Fresco is a painting technique that involves applying water-based pigments on freshly laid wet plaster. This method allows the paint to become an integral part of the wall as it dries, which can create a durable and vibrant artwork. Frescoes have been historically used in large mural paintings, with notable examples found in churches and public buildings, where the technique enhances the depth and richness of the artwork as it absorbs into the plaster.

In contrast, the other techniques listed, such as intaglio, involve engraving on a surface rather than painting on wet plaster; paper mache focuses on creating three-dimensional forms using paper and glue; and dioramas are miniature models that often represent scenes and can incorporate various materials but do not rely on the fresco technique. Each of these alternatives has its unique processes and tools distinctly separate from the principles of fresco painting.