By Umberto Veronesi, Mario Bandiera, Marcia Villarigues, Andreia Ruivo, Marta Manso, Susana Coentro
The ChromAz project tells the story of sixteenth- to eighteenth-century Portuguese azulejos from the perspective of colour technology. Tiles are a crucial piece of Portuguese national heritage, and artists had a broad palette of colours at their disposal. We started with one of the most complex to achieve: a pigment known as Naples yellow (lead antimonate), a product of human craft with a long history.
As one of the very first artificial materials, Naples yellow was employed from the Late Bronze Age (ca. 1500 BC) and initially linked to the production of opaque yellow glass. After disappearing from the European tradition for over a millennium, the pigment resurfaced in the sixteenth century, used by Venetian glassmakers, in oil paintings and in decorated glazed ceramics.
Around this time, technical texts begin to feature recipes for the manufacture of Naples yellow. Besides the lead-antimony base, authors list a number of other reagents, but only vaguely (if at all) describe the chromatic effects brought by the additions of these ingredients. So, to gain insights into such an important aspect of the early modern artistic process, we replicated eight recipes, summarised in Table 1.
Four recipes (Mariani I and II, Piccolpasso and Marmi 126) are simple, binary lead antimonates to which salt or tartar (or both) were added as fluxes to facilitate the reaction. The remaining four (Mariani III, Marmi 136, Darduin and Danzica) are ternary variants of the pigment. They can come with or without fluxes but, importantly, they contain what the authors refer to as tutty or tuccia, which scholars have variably interpreted as either zinc or tin oxide. To evaluate differences, we made two sets, one with the former and one with the latter, bringing the total to twelve re-worked recipes.
After thoroughly mixing the ingredients, we fired the raw pigments at 950°C for five hours and left them in the furnace to cool down to room temperature. Finally, we collected the mixtures, which had turned yellow, and ground them to a fine powder to homogenise the colour (Figure 2).
As the images show, variations in the recipes resulted in remarkably different hues, ranging from pale to bright yellow and all the way to dark orange. Adding zinc tends to darken the colour, while tin makes it lighter, as previous works already indicated (Figure 3A). The one yellow with calcina (lead and tin calcined together) is also made somewhat paler, due to the action of tin (Figure 3B).
However, it was more interesting to find out that fluxes have an equally crucial role in defining the chromatic characteristics of the pigment. We found out that salt invariably makes the pigment lighter in colour. On the other hand, the recipes containing tartar as the main flux display a darker, reddish hue (Figure 4).
Re-working lead antimonate recipes provided access to the wide chromatic palette that Renaissance artists could rely on. The pigment could be adjusted to be proper yellow or more orange-red, depending on users’ needs. Importantly, this flexibility also meant that recipes could be tweaked to accommodate issues of materials’ availability. Our work is still very much in progress, but it shows how performative methods complement information from texts and material culture and give them new context, throwing more decisive light on the act of art-making in the past.
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