
Turnsole, katasol, or folium was a dyestuff prepared from the annual plant ''
Chrozophora tinctoria
''Chrozophora tinctoria'' (commonly known as dyer's croton, giradol, turnsole or dyer's litmus plant) is a plant species native to the Mediterranean, the Middle East, India, Pakistan, and Central Asia. It is also present as a weed in North Americ ...
''.
History
Turnsole became a mainstay of medieval
manuscript illuminators
A manuscript (abbreviated MS for singular and MSS for plural) was, traditionally, any document written by hand or typewritten, as opposed to mechanically printed or reproduced in some indirect or automated way. More recently, the term has c ...
starting with the development of the technique for extracting it in the thirteenth century, when it joined the vegetable-based
woad
''Isatis tinctoria'', also called woad (), dyer's woad, dyer's-weed, or glastum, is a flowering plant in the family Brassicaceae (the mustard family) with a documented history of use as a blue dye and medicinal plant.
Its genus name, ''Isati ...
and
indigo
InterGlobe Aviation Limited (d/b/a IndiGo), is an India, Indian airline headquartered in Gurgaon, Haryana, India. It is the largest List of airlines of India, airline in India by passengers carried and fleet size, with a 64.1% domestic market ...
in the illuminator's repertory.
Its use was mostly as substitute of the more expensive Tyrian purple, the famous dye obtained from Murex molluscs. However, the queen of blue colorants was always the expensive
lapis lazuli
Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. Originating from the Persian word for the gem, ''lāžward'', lapis lazuli is ...
or its substitute
azurite
Azurite or '' Azure spar'Krivovichev V. G.'' Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0. ''(in Russian)'' is a soft, deep-blue copp ...
, ground to the finest powders. Turnsole was downgraded to a shading glaze and fell out of use in the illuminator's palette by the turn of the seventeenth century, with the easier availability of less fugitive mineral-derived blue pigments.
According to its method of preparation, turnsole produced a range of translucent colors from blue, through purple to red, depending on its reaction to the acidity or alkalinity of its environment, in a chemical reaction, not understood in the Middle Ages, that is most familiar in the
litmus test.

''Folium'' ("leaf"), was actually derived from the three-lobed fruit (''illustration''), not the leaves, and medieval recipes are explicit that the fruits must not be broken, or the seeds released, during production of the pigment.
The fruits were collected in autumn (August, September).
In the early fifteenth century,
Cennino Cennini
Cennino d'Andrea Cennini (; – before 1427) was an Italian painter influenced by Giotto. He was a student of Agnolo Gaddi in Florence. Gaddi trained under his father, called Taddeo Gaddi, who trained with Giotto. He is remembered mainly f ...
, in his ''Libro dell' Arte'' gives a recipe "XVIII: How you should tint paper turnsole color" and "LXXVI To paint a purple or turnsole drapery in fresco." (though neither of these recipes use or describe turnsole). Textiles soaked in the dye vat would be left in a close damp cellar in an atmosphere produced by pans of
urine
Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...
. It was not realized that the decomposition of
urea
Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...
in the urine was producing
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
, but the technique reminds us how foul-smelling was the dyer's art.
It was sold impregnated into small pieces of linen and then extracted for use. The colour has been attributed to several different chemicals, including an
anthocyanin
Anthocyanins (), also called anthocyans, are solubility, water-soluble vacuole, vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart named a chemical compou ...
.
Production of the pigment is described in a 15th century manuscript and this was used as the basis of producing the dye.
Although the plant extracts do contain several anthocyanins, the colour is due to
chrozophoridine
Chrozophoridin is a chemical used as a dye.
It is derived from the plant '' Chrozophora tinctoria'' (commonly known as dyer's croton, giradol, or turnsole), which is a species native to the Mediterranean, the Middle East, India, Pakistan, and Ce ...
, a hermidin derivative.
Turnsole was used as a food colorant, mentioned in ''Du Fait de Cuisine'' which suggests steeping it in milk. ''The French Cook'' by
François Pierre La Varenne
François Pierre de la Varenne (, 1615–1678 in Dijon), Burgundian by birth, was the author of ''Le Cuisinier françois'' (1651), one of the most influential cookbooks in early modern French cuisine. La Varenne's book expressed the culinary inn ...
(London 1653) mentions turnsole grated in water with a little
powder of Iris. It was also used to dye red the rind of a cheese from the Netherlands.
Herbal
A herbal is a book containing the names and descriptions of plants, usually with information on their medicinal, Herbal tonic, tonic, culinary, toxic, hallucinatory, aromatic, or Magic (paranormal), magical powers, and the legends associated wi ...
s indicated that the plant grows on sunny, well-drained Mediterranean slopes and called it ''solsequium'' ("sun-follower") from its habit of turning its flowers to face the sun; alternatively it might be called "Greater Verucaria";
[So named in a recipe for producing the colorant, ''Pro tornasolio faciendo'', ]British Library
The British Library is the national library of the United Kingdom. Based in London, it is one of the largest libraries in the world, with an estimated collection of between 170 and 200 million items from multiple countries. As a legal deposit li ...
, Sloane MS 1754, folio 235 verso, quoted in Daniel V. Thompson, Jr., "Medieval Color-Making: Tractatus Qualiter Quilibet Artificialis Color Fieri Possit from Paris, B. N., MS. latin 6749", ''Isis'' 22.2 (February 1935, pp. 456–468) p 458 note. early botanical works gave it synonyms of ''Morella'', ''Heliotropium tricoccum'' and ''Croton tinctorium''.
Medicinal uses
Medicinal properties were ascribed to it in the first century AD by Dioscorides in ''De Materia Medica'' and also in medieval pharmacopoeia texts.
There have now been studies in the 21st century demonstrating that it did not have significant anti-inflammatory properties.
Notes
{{Reflist
External links
TurnsoleAAAS 2020 article
Herbs
Illuminated manuscripts
Food colorings