Buon Fresco (also kown as True Fresco) is an ancient painting method, with its beginnings in Egyptian, Greek, and Roman times. Not reaching its full development and expression until the Renaissance, Buon Fresco is painting on the medium of wet plaster with pure pigments. The pigment becomes locked under the calcium carbonate skin of the plaster as it cures, creating an extraordinarily long-lasting and beautiful painting.
The advantage of Buon fresco is its durability. In fresco-secco, by contrast, the color does not become part of the wall and tends to flake off over time. The chief disadvantage of Buon fresco is that it must be done quickly without mistakes.  The painter plasters and paints only as much as can be completed in a day, which explains the Italian term for each of these sections, giornata, or a day’s work.  The size of a giornata varies according to the complexity of the painting within it.  A wall to be frescoed is typically prepared with a rough, thick undercoat of plaster known as the arriccio. When this was dry, a skim coat or intonico coat is placed which on the wall.