A brief overview of gilding techniques

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Before finally examining the use of gold within the panels, it is crucial to outline the different techniques with which it was applied, as they prove essential in understanding its intended effects.72 Gold appeared on pre-Eyckian and early Netherlandish panel painting in four forms: burnished leaf (or water gilding), which might be applied over a poliment such as bole—a technique also common in illuminated manuscripts—or directly onto the prepared ground, which is also referred to as ground gilding;73 flat unburnished leaf (also commonly called mordant gilding), applied over a mordant (adhesive) which might or might not be oil-based; gilded applied relief, unburnished gold leaf applied with a mordant over pre-formed relief decoration; and shell gold, gold ground into a powder and applied in effect like gold paint.

Before gilding or painting, the panel surface was always extensively prepared first with smoothed layers of (usually) chalk. Gold leaf to be burnished was laid either directly onto this ground—moistened so that the leaf would stick, hence the term water gilding—or over an intermediate layer of a moistened poliment, usually bole, a reddish-brown iron oxide clay, which enriched the colour as well as provided a cushion for working.74 The leaf was then burnished with a smooth stone or animal tooth to a high polish, and it might subsequently be tooled with punched designs, analogous to objects made of solid metal like the gilded triptych (Fig. 3). The full effect of burnished gold rarely survives today in panels because of abrasion to the delicate leaf, though it is often better preserved in illuminated manuscripts.75 Extensive tooled water gilding appears (if now heavily worn) on many pre-Eyckian paintings, including the Champmol panels discussed above (Fig. 5, Fig. 6), the Tower Retable now in the Meyer van den Bergh Museum in Antwerp, the quadriptych panels divided between Antwerp and Cleveland, and Melchior Broederlam's painted exterior wings on one of the Champmol carved altarpieces (Fig. 30).76 However, with the major exception of Rogier van der Weyden's Medici Madonna (Fig. 10), the ars nova painters stopped burnishing their gold leaf, and any gold still applied was usually not worked with the intention of making it look like solid metal in the manner of pre-Eyckian panels.

Unburnished leaf was generally a little thinner than the leaf used for burnished gilding,77 and it was typically applied after most of the panel had been painted, unless it formed a background. Early Netherlandish oil mordant was often made of light-coloured pigments blended with a little linseed oil, like a thick oil paint, applied to the panel where desired and the gold leaf laid on when it had reached the right degree of tackiness.78 The chemical properties of oil preclude overlying gold leaf from being burnished—at most it can be gently buffed, or the leaf will tear—but leaf applied over a non-oily ground would also technically be termed mordant gilding as long as it was left unburnished.79 This type of gold background appears in a few early Netherlandish panels (Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 31), though more often panels contain smaller areas of unburnished leaf applied with oil mordant (e.g. Fig. 21, Fig. 22). Mordant gilding has a matte appearance compared to undamaged water gilding, though it still reflects light very differently than paint simulating metal, only in a more diffuse gleam than the concentrated highlights of burnished leaf.

Gilded applied relief uses the mordant technique but with the gold leaf applied onto raised decorative motifs made of a plaster-like substance. These motifs were either built up freehand on the ground of the panel in pastiglia, or cast in a mould and glued onto the panel, usually made with tin foil backed by a filler (since tin, unlike gold alone, has the strength to hold a cast shape). Gilded reliefs could be used either for backgrounds, as in the Hendrik van Rijn panel (Fig. 4), the Seilern Triptych in the Courtauld Gallery, and the Thief to the Left of Christ in Frankfurt (Fig. 33), or for particular decorative motifs, in that era usually in the form of applied brocades (Figs. 15, Fig. 28a). Regardless of the type of mordant used, the uneven surface of relief prevented overlying gilding from being burnished, so like flat unburnished leaf it is always comparatively matte.80 Only a very few early Netherlandish panels used applied reliefs, mostly in the form of applied brocades, and they largely disappeared from panel painting by mid-century other than in the wing panels of certain Brabantine sculpted altarpieces towards the end of the century.81 Shell gold, finally, consisted of gold leaf ground into a powder, either applied onto mordant or mixed with a little oil or animal glue and painted on. It was usually reserved for small details and highlights, particularly within manuscript illumination—as mastered especially by the French court painter and illuminator Jean Fouquet—though occasionally on panels as well, where it can sometimes be difficult to distinguish visually from mordant gilding (Fig. 26, Fig. 26a).82

From the outset early Netherlandish painters no longer burnished their leaf (other than Rogier's Medici Madonna), and beyond a handful of early experiments they also abandoned gilded applied relief, even though both of these techniques were still applied to sculptural polychromy.83 In other words, painters soon eliminated the most non-painterly techniques for working with panels, and instead reserved them for sculpture. Large areas of gold for backgrounds were usually substantially overpainted to incorporate them into the representation, and smaller areas of mordant gilding were increasingly reserved for heavenly phenomena like halo rays rather than earthly objects. These trends developed over a period of experimentation, particularly concentrated in the 1420s-40s.

72 The following largely derives from David Bomford et al., Italian Painting Before 1400: Art in the Making (London, 1989), 21-26, 43-48; Billinge et al., 'Methods and materials', 30-34; and Jilleen Nadolny, 'All that's burnished isn't bole. Reflections on medieval water gilding part 1: early medieval to 1300', in Medieval Painting Techniques in Northern Europe: Techniques, Analysis, Art History, ed. Jilleen Nadolny (London, 2006), 148-62.

73 This term was invented by Jilleen Nadolny in her unpublished 2001 dissertation; see 'All that's burnished isn't bole', 151.

74 Ibid., 155-56.

75 Bomford et al., Italian Painting Before 1400, 23-24. On manuscripts see Kathleen P. Whitley, The Gilded Page: The History and Technique of Manuscript Gilding (London, 2000). In contrast to panel painting terminology she uses 'mordant' to describe burnished leaf adhesives, employed in both flat and raised gilding; the former was usually composed of gum arabic, egg white, or garlic juice, whereas the latter was a gesso sottile mixture with bole. Given that manuscripts do not use oil paint, both flat and raised leaf can be burnished and punched, though raised leaf achieves more polish (see ch. 4-5). Unburnished gilding appears in manuscripts as shell gold.

76  Christina Currie, 'Genesis of a pre-Eyckian masterpiece: Melchior Broederlam's painted wings for the Crucifixion Altarpiece', in Stroo, Pre-Eyckian Panel Painting, vol. 2, 23-86; in the same volume, Livia Depuydt-Elbaum, 'Scenes from the infancy of Christ: the Tower Retable in the Mayer van den Bergh Museum. Preliminary study - restoration - observations', 87-120; Hélène Mund, Cyriel Stroo, and Nicole Goetghebeur, The Mayer van den Bergh Museum, Antwerp (Brussels, 2003), 202-87.

77 Bomford et al., Italian Painting Before 1400, 22; Binski and Massing, The Westminster Retable, 239.

78 On the components of northern European oil mordant see Billinge et al., 'Methods and materials', 31-32.

79 Nadolny, 'All that's burnished isn't bole', 150. In practice, however, 'mordant gilding' is often equated with oil mordant rather than with the leaf being unburnished; thus, for example, the unburnished gold leaf background of the Rogier van der Weyden Madonna and Child in the Huntington Gallery is described as ground-gilded in Cathy Metzger and Griet Steyaert, 'Painting, a distinct profession', in Campbell and Stock, Rogier van der Weyden, 162-79, at 174, and as water gilded in the catalogue entry, 318, intended to indicate not that the leaf was burnished but that it was laid directly onto the moistened prepared ground. My thanks to Catherine Metzger, senior conservator of paintings at the National Gallery, Washington, for explaining their use of terminology; personal communication, 9 February 2012.

80 Geelen and Steyaert, 'Relief decorations in the art of around 1400'.

81 Imitation and Illusion, 39.

82 Currie, 'Genesis of a pre-Eyckian masterpiece', 65; Lawson, 'The Belles Heures of Jean, duc de Berry', 154.

83 On these techniques in carved altarpieces see Myriam Serck-Dewaide, 'Support and polychromy of altarpieces from Brussels, Mechlin, and Antwerp: study, comparison, and restoration', in Painted Wood: History and Conservation, ed. Valerie Dorge and F. Carey Howlett (Los Angeles, 1998), 82-99; for more detailed images see the version published in Marjan Buyle and Christine Vanthillo, eds, Vlaamse en Brabantse retabels in Belgische monumenten (Brussels, 2000), 87-104.