My research into the collection focuses specifically on the artists’ use of the dye-based pigment known as ‘red lake’. After the initial examination of the paintings in both visible light and ultraviolet induced-visible fluorescence, it became clear early on that nearly every painting contained red lake. The way in which the pigment was used varied not only amongst the artists, but throughout a single painting. An example of this can be seen in a painting attributed to Nehemiah Partridge entitled Portrait of Gerritt Teunis van Vechten (c. 1719) (fig. 1). The red lake medium was best identified through a technique called ‘cross section analysis’ whereby a small sample (roughly the width of four human hairs) is taken from an area of loss in the painting, mounted in an epoxy, then ground and polished along the side to reveal the stratigraphy of the paint layers, similar to cutting into a piece of cake. In the first sample taken from the menacing red sky, a thin layer of medium-rich red lake was applied over a deep red ground (fig. 2a). This use of the lake pigment allowed for the transparency of the red lake to intensify the opaque ground resulting in a vibrant scarlet hue. The second sample taken from the sitter’s rosy cheek revealed the artists use of red lake in combination with lead white to create a pale pink (fig. 2b). This was liberally applied over the red ground creating an opaque rosy skin tone. This varied use of red lakes was seen throughout the series of portraits. The lake was used as a glaze in the skies to create a rich background, mixed with lead white to create a rouge in the sitter’s faces, and mixed with the red mercury-based pigment called ‘vermillion’ to make the striking crimson costumes and accessories. In addition to exploring the artists’ use of lakes, my goal has been to identify and characterize the source of the dyestuff through scientific analysis and workshops that focus on recreating the lake pigments from historic recipes. This technical bulletin addresses the latter, shedding light on the process used to create such a vibrant and versatile shade a red.

Growing up in southwestern Arizona, I became all too accustomed to the white webbing that sprung up on the paddles of the prickly pear cactus over the hot summer months. As a child, I never had any desire to unearth whatever creature made that their home, but as a postgraduate fellow studying red lakes, I was eager to research this curious bug. Cochineal is a small, scale insect that feeds on the nutrients of the prickly pear (figs. 3-4). It spins the white webbing in order to protect itself from the intense desert sun, and as a defense mechanism against other insects, it produces carminic acid, from which the red dyestuff is derived. Cochineal is native to South America and parts of the American southwest. While today Peru serves as the main source for the insect, in the early 18th century Americas, Mexico had exported it both north to the New World and across the Atlantic to Spain after the colonization of Mexico by the Spanish [3]. Cochineal was in high demand by the British Army during this time, as the colorant extracted from the insects was used to dye the red coats of their military uniform [4].

The colorant madder, also known as ‘rose madder’, ‘Turkey red’ or ‘dyer’s madder’ depending on the manufacture process, is native to the Middle East and eastern Mediterranean (figs. 5-6) [5]. The dyestuff is obtained by harvesting the root of the plant species Rubia tinctorum after two years of cultivation. Madder differs from other dyestuff in that it can produce a wide range of hues ranging from orange to burgundy depending on the pH and temperatures of the dye bath during extraction. Due to it being a plant structure, the root material is a complex mixture of several components, the most important for creating a dye are pseudopurpurin, purpurin, and the acid ruberthyrin [6]. Compared to cochineal, extracting a dye from madder is fairly simple. However, similarly to cochineal, the dye is light sensitive.