<P> 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 . </P> <P> 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 face, for instance, might take an entire day, whereas large areas of sky can be painted quite rapidly . </P> <P> One of the first painters in the post-classical period to use this technique was the Isaac Master in the Upper Basilica of Saint Francis in Assisi . </P> <P> In medieval and Renaissance Italy, a wall to be frescoed was first prepared with a rough, thick undercoat of plaster known as the arriccio . When this was dry, assistants copied the master painter's composition onto it with reddish - brown pigment or charcoal . The artist made any necessary adjustments . </P>

Buon fresco is not a medium which can be easily altered