Each day, another section of the painting is added to the previous day's work until the image is fully completed. The seams around each day's work must be skillfully negotiated in order that they not be too visible in the end product, although some evidence of them does exist in the completed painting, and is considered one of the hallmarks of a true fresco.
Because the fresco is separated into many days work, its various sections may have some slight variations in tone. When the plaster is fully dried then, a "secco" technique involving mixing pigments with egg yolk is applied and the painting sections are blended and refined if necessary.