Because the plaster must be painted while it is wet, Karla puts the intonaco only in an area she can finish by the end of that day. This patch of wet plaster is called the "day section" (giornata).
To create the paint, earth pigments must be ground to an ultra-smooth consistency by using a stone muller (a mallet-like tool), then dissolved in distilled water. This grinding can take hours and must be performed properly to ensure the stability of the pigments in the plaster.
Unlike an acrylic or oil painting, a fresco cannot be painted over. If the artist is dissatisfied with some part, he or she must first scrape off the intonaco, then replaster and repaint the entire day section. As the painted fresco dries, calcium hydroxide in the plaster combines with carbon dioxide in the air to form calcium carbonate, which permanently fuses pigment and plaster.