How Were Frescoes Made?
A fresco is the result of painting of fresh plaster with colored pigments of mineral origin dissolved in water. When the surface dries, the color is incorporated into the plaster thanks to a chemical process, thus allowing the painting to remain for a potentially unlimited period of time, even outside. The method of painting frescoes, used in Roman times and by the great masters of the Italian Renaissance including Giotto, Raphael, and Michelangelo.
For a mural painting, the surface has to be smooth and of a uniform color. For this reason, the wall which is to be painted is covered by a coat called plaster, made up of hydrated lime and river sand. The next process is called “slaked lime” which makes the surface even smoother. This slaked lime is obtained by firing at 900° river stone3s or pebbles, made up essentially of calcium carbonate. The pebbles become a powde, giving rise to what is known as “quicklime”. This quicklime is plunged into water for about six months because otherwise it would burn the colors. This greasy paste (slaked lime) its formula and it chemical reactions are fundamental for the pictorial technique of fescoes.
Fresco or “a buon fresco” painting is done by applying the color to the still fresh plaster, hense why it is called “a fresco” painting. The difficulity of the fresco technique is the need to work while the plaster on the wall is still wet. The artist laid out his scene with drawing in charcoal.