The frescoes in the great hall were brought back to light during the 1998 restoration. Beneath centuries of candle smoke and 19th-century repainting, conservators rediscovered the original ultramarine blue, made by grinding lapis lazuli imported from Afghanistan.
The buon fresco technique means painting onto still-damp plaster: the pigment sinks into the lime and becomes one with the wall. This is why each day's work — the so-called giornata — matches a defined portion of the fresco.