In Giotto's workshop
From old scaffolding to the orginal painting techniques
One of the most fascinating aspects of the close comparison and study of these wall paintings was the reconstruction of the operational phases of Giotto's work through the numerous marks on the plaster and the analysis of the pictorial materials belonging to the original phase, integrating the information already collected.
For the restoration staff it was like being back on the scaffolding with Giotto and his assistants when they discovered details such as the colour tests which the painters had used on some areas, destined to be painted dry: a series of coloured brushstrokes to test precisely the change in tone produced by the drying of the plaster, which would then disappear from view with the dry chromatic application and which are now revealed only through the loss of these backgrounds.
First of all, it is possible to specify the construction of Giotto's “boxes”, that is, the wooden structure that was used by the painters and which allows us to retrace the progress of the work: observing the series of scaffolding holes identified only thanks to thermo vision (that is the examination by means of a thermal camera of the inhomogeneity of the wall structure) it is clear that Giotto's scaffolding must have been placed first of all halfway up the level of the lunettes, to be able to paint the vault. It was then brought to the base of each scene, with the beams inserted into the walls, using movable wooden beams to reach the highest areas of each level, which was completed until the metal leaves were applied (the last finishing phase) before moving on to the lower area.
Giotto then traced the entire sketch of each scene and on this the dimensions of the giornate of the tonachino (plaster), were decided, that is, the plaster on which the painters would spread the colours. These are larger for the backgrounds and mostly geometric, and smaller for the figures.
Giotto’s colour palette is composed of pigments of natural origin, such as yellow, red and green earth, lime white, and others manufactured by specialized workshops to obtain pigments with different characteristics, more vivid or more opaque: lead white, copper blue (azurite), cinnabar. The technique, precisely because of the presence of the giornate, was that of the fresco, but Giotto chose some areas to dry paint, that is, using an organic binder, most likely egg, with almost dry plaster.