Incomparably the most important yellow in medieval painting is the metal gold. Yellow pigments, however, played a significant part in the pageant of medieval technique. One of the most important services required of them was to imitate the appearance of gold. Another of their chief functions was to modify the qualities of greens, and to a less extent, of reds. Of all their uses, perhaps the least important was to represent yellow things.
???Daniel Thompson, The Materials and Techniques of Medieval Painting
The vegetable yellows used in medieval illumination were more readily prepared and much safer to use than mineral yellows like realgar or orpiment. Above, left: The brilliant red-orange stigmas of the autumn-blooming saffron crocus, used by medieval cooks as a colorant and a seasoning, were also exploited by illuminators. Right: Flower spikes of weld, the most ancient yellow dyestuff known. When processed as a pigment, this weedy biennial provided manuscript painters with a bright vegetable yellow.
A number of plants were exploited for coloring matter in the Middle Ages, whether to tint foodstuffs or to furnish dyes and pigments. By no means all, or even many, artist’s pigments were of vegetable origin; mineral colors were used for wall painting, where the more delicate and fugitive nature of vegetable colors was inappropriate. In book painting, a combination of vegetable and mineral colors was employed. The same plant that yielded a dye for textiles could be prepared as a pigment and used by illuminators. Several species produced a viable yellow, including weld, saffron, and celandine; as Daniel Thompson observes, these vegetable yellows served both to imitate the appearance of gold, and to modify greens and reds.
Weld (Reseda luteola) is a hardy annual or biennial herb. Native to south-central and western Europe, and widely naturalized throughout Europe, west and central Asia, and North Africa, it is thought to be the most ancient of yellow dyestuffs, utilized as early as the Neolithic period. It was preferred to all other vegetable yellows in the Middle Ages because of its relative permanency. (Weld was specified for the production of tapestries of high quality, including the Unicorn Tapestries. Nevertheless, the weld yellows and greens in medieval tapestry have proved far more fugitive than the vegetable blues and reds derived from madder (Rubia tinctorum) and woad (Isatis tinctoria).
The organic coloring matter in a dye solution could be mixed with, and chemically bound to, an inorganic base, such as chalk or clay. This preparation is known as lake; the mineral salts that bind the color to the base are called mordants. The color was precipitated out as an insoluble pigment that could be stored and ground as needed. The importance of weld as an artist’s pigment, rather than a dye, dates to the fourteenth century. A decoction of weld, made by chopping the leaves and flowering tops of the plant and steeping them in boiling water, might then be mixed with chalk and alum to create a weld lake. According to Daniel Thompson, weld lakes were used chiefly by manuscript painters, providing a bright vegetable yellow which could be substituted for the poisonous minerals known as orpiment and realgar, also used to imitate gold. (See the Eytmology Explorer website for the origins of the names orpiment and realgar.) In an appendix to The Art of Illumination devoted to technical observations on the richly illustrated Belles Heures manuscript, conservator Margaret Lawson notes that orpiment was commonly used, although recognized as problematic.
The preparation and use of pigments is described for us in manuals like Cennino Cennini’s important work, Il Libro dell’Arte (The Crafsman’s Handbook), which describes techniques founded in thirteenth- and fourteenth-century practice, although it may date to the early fifteenth century. The toxic nature of orpiment and realgar, both sulfides of arsenic, was recognized, as we see from the section of The Craftsman’s Handbook devoted to colors:
This color is an artificial one. It is made by alchemy, and it is really poisonous. And in color it is a handsome yellow more closely resembling gold than any other color. . . And this color . . . is the most refractory color to work up that there is in our profession. . . When you have got it powdered , put some clear water on it, and work it up as much as you can . . . Beware of soiling your mouth with it, lest you suffer personal injury. (On the Character of A Yellow Called Orpiment. Chapter XLVII)
Realgar was known to be even more dangerous:
This color is really poisonous. We do not use it, except sometimes on panel. . . There is no keeping company with it . . . It has to be ground a great deal with clear water. And look out for yourself. (On the Character of a Yellow which is called Realgar. Chapter XLVIII)
Two other vegetable yellows grown at The Cloisters were used as gold substitutes in the Middle Ages: saffron (Crocus sativus) and the greater celandine (Chelidonium majus). Long prized for its fragrance and savor as well as its color, saffron has been cultivated since ancient times and no longer exists in its wild form. The dried red-orange stigmas of the pale lilac flowers yield the spice. Saffron crocus blooms not in spring but in autumn, and the narrow grassy leaves continue to grow throughout the winter. The corms should be planted in well-drained soil in a warm, sunny location, preferably in late summer. Whether for culinary or artistic purposes, the thread-like stigmas should be picked out by hand as soon as the flowers open and dried immediately in the sun or a gentle heat, before being stored in the dark, in an airtight container. Some sixty thousand flowers are required to render an ounce of pure saffron. Only a few threads were necessary to yield a dish of color. (For more on celandine, see “Swallow Wort,” May 6, 2011.)
Both saffron and celandine yielded their color readily and were simpler to prepare than a weld lake. Either saffron threads or the bright orange latex expressed from the broken stems of celandine could be mixed with egg yolk and painted over powdered silver or tin to achieve the effect of gold. Of the two, saffron was the more important colorant in medieval book painting, although it was known to lose color over time when exposed to air. A pinch of the dried stamens of the saffron crocus were infused in a dish of glair (the white of an egg), which was beaten to a froth and left to stand. A “clothlet” soaked in saffron might also be dried and put into a dish with gum arabic, a resin derived from several species of acacia. While the transparent yellow tincture which resulted was sometimes used to enrich other colors???a very creditable grass green could be achieved by mixing saffron with verdigris???it was sometimes used alone for ornamental pen flourishes around colored initials or panels, and for golden glazes or highlights.
Cannon, John and Margaret. Dye Plants and Dyeing. Illustrated by Gretel Dalby-Quenet. Published in association with Royal Botanic Gardens, Kew. London: Herbert Press, 1994.
Cennini, Cennino Andrea. The Craftsman’s Handbook “Il Libro dell’Arte”. Translated by Daniel V. Thompson, Jr. Reprint of 1933 Yale University Press edition. New York: Dover, 1954.
Husband, Timothy B. The Art of Illumination. New York: The Metropolitan Museum of Art, 2008.
Thompson, Daniel V. The Materials and Techniques of Medieval Painting. With a forward by Bernard Berenson. Reprint: New York: Dover Publications, 1956.