Vermilion, also spelled vermillion, when found naturally-occurring, is an opaque orangeish red pigment, used since antiquity, originally derived from the powdered mineral cinnabar. Chemically the pigment is mercuric sulfide, HgS. Like all mercury compounds it is toxic.
Today, vermilion is most commonly artificially produced by reacting mercury with molten sulfur. Most naturally produced vermilion comes from cinnabar mined in China, giving rise to its alternative name of China red.
As pure sources of cinnabar are rare, natural vermilion has always been extremely expensive. In the Middle Ages, vermilion was often as expensive as gilding. As of 2007 a 40 ml tube of genuine Chinese Vermilion oil paint can cost £51 (US ~$100) .
In painting, vermilion has largely been replaced by the pigment cadmium red, a pigment that is less reactive due to the replacement of mercury with cadmium, especially in certain applications such as watercolors. The last mainstream commercial source in watercolors was from the Belgian artist's materials company Blockx, although the pigment can still be obtained in oils, where it is considered more stable. Unlike mercuric sulfide, cadmium sulfide is available in a large range of warm hues, including hues obtained by the addition of selenium or zinc. The range is from lemon yellow to a dull deep red, sometimes referred to as "cadmium purple".
Vermilion is also the name of the typical color of the natural ground pigment, which is a bright red tinged with orange. It is somewhat similar to the color scarlet. Vermilion is not on the color wheel since the color is mixed with a slight amount of grey. As with cadmium sulfide,mercuric sulfide can be found in a range from a bright orange-toned red to a duller slightly bluish red. The differences in hue are due to the range in the size of the ground particles. The larger the average crystal is, the duller and less orange-toned it appears. It has been theorized that the more coarsely ground "Chinese" form of vermilion is more permanent than the more orange "French" variety. It is also theorized that purification leads to increased stability, as with many other pigments.
Hindu women use vermilion known as Sindoor, after they are married.
Additional recommended knowledge
There is evidence of the use of cinnabar pigment in India and China since prehistory; It was known to the Romans; Pliny the Elder records that it became so expensive that the price had to be fixed by the Roman government. The synthesis of vermilion from mercury and sulfur may have been invented by the Chinese; the earliest known description of the process dates from the 8th century.The synthetically-produced pigment was used throughout Europe from the 12th century, mostly for illuminated manuscripts, although it remained prohibitively expensive until the 14th century when the technique for synthesizing vermilion was widely known in Europe. Synthetic vermilion was regarded early on as superior to the pigment derived from natural cinnabar. Cennino Cennini mentions that vermilion is
"made by alchemy, prepared in a retort. I am leaving out the system for this, because it would be too tedious to set forth in my discussion all the methods and receipts. Because, if you want to take the trouble, you will find plenty of receipts for it, and especially by asking of the friars. But I advise you rather to get some of that which you find at the druggists' for your money, so as not to lose time in the many variations of procedure. And I will teach you how to buy it, and to recognize the good vermilion. Always buy vermilion unbroken, and not pounded or ground. The reason? Because it is generally adulterated, either with red lead or with pounded brick." 
Vermilion was frequently adulterated due to its high price, usually with red lead, an inexpensive bright lead oxide pigment that was too reactive to be trustworthy enough for use in art.
"American Vermilion" is the name for a historical vermilion imitation. The words for the color red in Portuguese vermelho and Catalan vermell derive from this term.
"China red" is another name for the pigment vermilion, which is the traditional red pigment of Chinese art. Chinese name chops are printed with a red cinnabar paste, and vermilion (or cinnabar) is the pigment used in Chinese red lacquer. Cinnabar also has significance in Taoist culture, and was regarded as the color of life and eternity.