Indian yellow, also called
euxanthin or
euxanthine, is a
xanthonoidA xanthonoid is a chemical natural phenolic compound formed from the xanthone backbone. Many members of the Clusiaceae contain xanthonoids.Xanthonoid biosynthesis in cell cultures of Hypericum androsaemum involves the presence of a benzophenone synthase condensing a molecule of benzoyl-CoA with...
. It is transparent yellow
pigmentA pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
used in
oil paintOil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnish may be added to increase the glossiness of the...
. Chemically it is a
magnesium euxanthate, the
magnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
salt of
euxanthic acid. It is a clear, deep and luminescent yellow pigment. Its color is deeper than
gambogeGamboge is a partially transparent dark mustard yellow pigment.Other forms and spellings are: cambodia, cambogium, camboge, cambugium, gambaugium, gambogia, gambozia, gamboidea, gambogium, gumbouge, gambouge, gamboge, gambooge, gambugia...
but less pure than cadmium yellow.
Indian yellow is a
glycosideIn chemistry, a glycoside is a molecule in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme...
, a conjugate of the
aglyconeAn aglycone is the non-sugar compound remaining after replacement of the glycosyl group from a glycoside by a hydrogen atom. The spelling aglycon is sometimes encountered .Classes of phytochemicals found in the aglycone and glycosides forms :...
euxanthone with
glucuronic acidGlucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
, making the
chromophoreA chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...
euxanthone much more water-soluble.
Indian yellow was used by artist
painterPainting is the practice of applying paint, pigment, color or other medium to a surface . The application of the medium is commonly applied to the base with a brush but other objects can be used. In art, the term painting describes both the act and the result of the action. However, painting is...
s in both
oil paintingOil painting is the process of painting with pigments that are bound with a medium of drying oil—especially in early modern Europe, linseed oil. Often an oil such as linseed was boiled with a resin such as pine resin or even frankincense; these were called 'varnishes' and were prized for their body...
s and watercolors. Due to its
fluorescenceFluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
, it is especially vivid and bright in
sunlightSunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
. It was likely first used by
DutchThe Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
artists, and before the end of the 18th century it was commonly used by artists across Europe. Its origin was unknown until an investigation in the year 1883; however, in 2004, Victoria Finlay called this into question.
History
Indian yellow pigment is claimed to have been originally manufactured in rural India from the urine of cattle fed only on
mangoThe mango is a fleshy stone fruit belonging to the genus Mangifera, consisting of numerous tropical fruiting trees in the flowering plant family Anacardiaceae. The mango is native to India from where it spread all over the world. It is also the most cultivated fruit of the tropical world. While...
leaves and water. The urine would be collected and dried, producing foul-smelling hard dirty yellow balls of the raw pigment, called "purree". The process was allegedly declared inhumane and outlawed in 1908, as the cows were extremely undernourished, partly because the leaves contain the toxin
urushiolUrushiol is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. . It causes an allergic skin rash on contact, known as urushiol-induced contact dermatitis...
which is also found in
poison ivyToxicodendron radicans, better known as poison ivy , is a poisonous North American plant that is well known for its production of urushiol, a clear liquid compound found within the sap of the plant that causes an itching rash in most people who touch it...
.
Nicholas Eastaugh reports in his
Pigment Compendium that a description of the above process was given by a Mr. T.N. Mukharji of Calcutta, who claimed to have studied the process in Monghyr, north-east Bihar, India. He describes how urine was collected in small pots, cooled, then concentrated over a fire. The liquid was then filtered through cloth and the sediment collected in balls, then dried over a fire and in the sun. Importers in Europe would then wash and purify the balls, separating greenish and yellow phases.
In "The Art of Painting in Oil and Fresco," by MJFL Merimee, originally published in 1839, Merimee states a possible source for the yellow
lakeA lake pigment is a pigment manufactured by precipitating a dye with an inert binder, usually a metallic salt. The word lake is a homonym of lake as body of water and does not refer to it....
:
...the coloring matter is extracted from a tree or large shrub, called memecylon tinctorium, the leaves of which are employed by the natives in their yellow dyes. From a smell like cow's urine, which exhales from this colour, it is probable that this material is employed in extracting the tint of the memecylon.
In 1844, chemist
John StenhouseJohn Stenhouse FRS FRSE FIC FCS was a Scottish chemist. In 1854, he invented one of the first practical respirators.He was a co-founder of the Chemical Society in 1841.-Life:...
examined the origin of Indian yellow in an article published in the November 1844 edition of the
Philosophical MagazineThe Philosophical Magazine is one of the oldest scientific journals published in English. Initiated by Alexander Tilloch in 1798, in 1822 Richard Taylor became joint editor and it has been published continuously by Taylor & Francis ever since; it was the journal of choice for such luminaries as...
. At that time the balls of purree imported from India and China came in balls of around 3 ounces (85 g) - 4 ounces (113.4 g) which when broken open showed a deep orange color. Viewed under a microscope, it showed small needle-shaped crystals, while its smell was said to resemble that of
castor oilCastor oil is a vegetable oil obtained from the castor bean . Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is and its density is 961 kg/m3...
. Stenhouse reported that Indian yellow was commonly thought to either be composed of
gallstoneA gallstone is a crystalline concretion formed within the gallbladder by accretion of bile components. These calculi are formed in the gallbladder, but may pass distally into other parts of the biliary tract such as the cystic duct, common bile duct, pancreatic duct, or the ampulla of...
s from different animals, including camels, elephants, and buffalos, or deposited from the urine of some of these animals. He carried out a chemical analysis and concluded that he believed it was in fact of vegetable origin, and was "the juice of some tree or plant, which, after it has been expressed, has been saturated with
magnesiaMagnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
and boiled down to its present consistence."
In her 2004 book
Color: A Natural History of the Palette, Victoria Finlay examined whether Indian yellow was really made from cow urine. The only printed source mentioning this practice is a single letter written by Mr. T.N. Mukharji, who claimed to have seen the color being made. Aside from this letter, there appear to be no written sources from the time period mentioning the production of Indian yellow. Finlay searched for legal records concerning the supposed banning of Indian yellow production in both the India Library in London and the National Library in Calcutta, and found none. She visited the town in India mentioned in Mukharji's letter as the only source of the color, but found no trace of evidence that the color had ever been produced there. None of the locals she spoke with had ever heard of the practice. It is possible that Indian yellow came from another source, and that the cow urine story was fabricated by Mukharji, but came to be accepted by later authors. As such, the viability of producing Indian yellow from the urine of mango-leaf-fed cows is unknown.
Modern day
The replacement for the original pigment (which was not entirely lightfast), synthetic
Indian yellow hue, is a mixture of nickel azo,
hansa yellowHansa Yellow is a synthetic Arylide Yellow pigment used in inks, oil paint, acrylic paint and other applications. Hansa yellows were first made in Germany just before World War I and are ASTM II lightfast and semitransparent....
and quinacridone burnt orange. It is also known as
azo yellow light and
deep, or
nickel azo yellow.