Among the techniques used for the gilding of a surface, water gilding, or bolus gilding, is the most widespread and appreciated so much that it is identified with tout court gilding. The procedure is extensively described by Cennino Cennini (late Fourteenth Century) and essentially consists of applying one or more coats of Armenian bole dissolved in colletta (glue) to the previously plastered and well-polished surface.
Once the surface has been smoothed again, a light layer of warm colletta diluted with water is applied to limited portions, applying the gold leaf and making sure that it adheres perfectly to the surface. The gilded surface is then burnished and then possibly decorated with burins and punches.
French: Dorure à l’eau – Italian: Doratura a guazzo – Spanish: Dorado al agua – German: Polimentvergoldung
The beauty of a gilding essentially depends on the materials and procedures adopted to apply the thin gold sheets to the support. The water gilding technique, with the use of the bole as a background, is certainly the procedure that leads to the best result and it is Cennino Cennini in his “Book of the Art” who reveals the secret of the great masters.
After having completed the drawing on a wood panel prepared with gypsum and glue the outlines of the figures are engraved with a pointed iron thus separating the areas that are to receive the gold from those to be painted in tempera. At this point, with a soft and flat brush, the bole mixed with an aqueous glue is spread over the entire surface to be gilded, taking care to maintain an even thickness and trying not to interrupt the brushstroke. And this to the point of carrying out, again according to Cennini’s advice, four successive layers using an increasingly dense compound.
Once the surface is perfectly smoothed with a linen cloth, the gold is applied: once the leaf is transported and spread on the cushion, it is cut with a special knife to bring it to the necessary measurements. Wet the small area to be browned with whipped egg white and water, take the leaf using the electrostaticity of the same brush. The gold leaf now delicately rests on it. Repeat the operation to cover a certain surface, the gold is perfectly adhered by pressing lightly with a cotton ball. Once the gilding is completed, the surface is subsequently polished, or burnished, and possibly enriched with punching or further pictorial interventions.