painting onto wet plaster
Fresco's weren't done in the middle ages. I think you are thinking of Renaissance artist Michelangelo.
giotto
The woman who painted over the fresco is Cecilia Gimnez, a Spanish amateur artist.
Do you mean wet or dry fresco? In both cases, you need alkali-resistent pigments. In wet fresco (the original fresco technique) they're mixed with the plaster used to finish the wall, in dry fresco (fresco secco) a paint is made with mainly caseine. I've seen an old recipe that involves fresh cheese (which contains caseine)
Diego Rivera
Two possible reasons: Oil paint on a smooth surface makes for easier painting small details than fresco paint on a wall. A fresco is usually a large-format mural, intended to be seen from a distance.
Fresco is created when earth tones are applied directly to wet plaster. The creation of paintings such as those within the Sistine Chapel were created in just such a manner.
The School of Athens is a famous fresco in the Vatican. It was painted in the early 16th century by Raffaello Sanzio, better known as "Raphael".
to make it easy
The fresco technique, which involves applying water-based pigments on freshly laid wet plaster, was notably utilized by the Italian artist Giotto di Bondone in the late 13th and early 14th centuries. While fresco painting has ancient origins, Giotto is often credited with its revival and significant advancement during the Renaissance. His works, such as those in the Scrovegni Chapel, exemplify the technique's potential for narrative and depth.
fresco
Leonardo da Vinci is the artist and scientist who painted the 'Last Supper'. The fresco is in the convent of Santa Maria delle Grazie in Milan. Considered to be in the movement of the Renaissance.