White

• 1. Introduction

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  White is the lightest possible color, and a perfectly white surface earns that title by doing something almost ungenerous with light. It absorbs nothing. Every visible wavelength that strikes it gets scattered back, no matter the wavelength or the spectral distribution. That refusal to keep any light is why snow, chalk, and milk look the way they do. But white is stranger than it first appears. There is, the color scientists tell us, no single unique specification of white light. A bulb labeled 2700K and one labeled 6000K both read as white, despite emitting very different spectra. So how does the eye settle on white at all, and why has a color with no fixed definition come to stand for purity, for mourning, for monarchy, and for surrender? Why did Roman office-seekers brighten their togas with chalk, and why has the pope worn white since 1566? The answers run from a paleolithic cave to a stellar remnant the size of the Earth.

• 2. How The Eye Decides

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  Light reaches the eye as white when it stimulates all three types of color-sensitive cone cells in roughly equal amounts. That is the whole trick on the perception side. On the object side, a surface looks white when it reflects back most of the light that strikes it in a diffuse way, scattering rather than mirroring. If the reflection were specular instead of diffuse, you would have a mirror, not a white surface. This split between source and surface matters. While there is no unique specification of white light, there is a unique specification of a white surface. A perfectly white surface diffusely reflects all visible light without absorbing any, irrespective of wavelength. Because it keeps none of the incident light, white becomes the lightest color available. The International Commission on Illumination defines an adapted white as a stimulus that a chromatically adapted observer would judge perfectly achromatic, with a luminance factor of unity. Color constancy holds an object's perceived color steady as illumination shifts across broadly whitish light. The same principle governs the white point in photography and cinematography, where the chosen white point transforms every other color stimulus. Manipulating that white point can even explain optical illusions such as The dress.

• 3. Breaking And Building Light

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  In 1666, Isaac Newton sent white light through a prism, split it into its component colors, then used a second prism to reassemble them. Before that experiment, most scientists believed white was the fundamental color of light. Edwin Babbitt, writing in 1878, proposed his own recipe, calling white a mix of five parts red, three parts yellow, and eight parts blue. The everyday machinery of white light is additive. On a television or computer screen, white comes from mixing red, green, and blue at full intensity, a process called additive mixing. White light can even be faked with only two wavelengths, mixing a red and cyan laser, or yellow and blue lasers, though such light distorts the color of objects badly. The reason two utterly different spectra can feel identical to the eye lies in how the visual system processes them, a match called a metamerism. Many natural sources, including sunlight and incandescent lamps, emit at nearly all visible wavelengths, which is why people sometimes call white a mixture of all colors. White pigment supplies the opposite case, since titanium dioxide is the pigment that gives white surfaces their color.

• 4. The Toxic Pigment Trade

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  Lead white was being produced as early as the 4th century BC, and the process appears in Pliny the Elder, Vitruvius, and the Greek author Theophrastus. Pieces of lead were sealed in clay pots beside a compartment of vinegar, then stacked near cow dung. The combined fumes corroded the lead into lead carbonate over a month or more. It made an excellent white and served artists for centuries, but it was toxic, and the Greeks had endured a long, laborious process to make it. Chalk preceded everything. A type of limestone made of calcite, it was deposited under the sea as the plates of micro-organisms called Coccolithophore, and it became the first white pigment used by prehistoric artists. The Renaissance painter Cennino Cennini described another option in the 15th century, Bianco di San Giovanni, made of dried lime soaked in water for eight days with the water changed daily, then formed into cakes and dried in the sun. The modern leader arrived later. Titanium white became commercially available in 1921, drawn from minerals including brookite, anatase, rutile, and ilmenite. With twice the coverage of lead white, its brilliance now colors most toothpaste and sunscreen. Zinc white, made from zinc oxide, is less opaque, and a variety made for artists is called Chinese white. Some materials are pushed past plain white using optical brightener agents, chemicals that absorb ultraviolet light around 340 to 370 nanometers and re-emit it as blue around 420 to 470 nanometers, sending out more visible light than they receive.

• 5. Whiteness In Nature

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  The White Cliffs of Dover owe their color to the chalk they contain, a limestone that reflects sunlight rather than absorbing it. Beaches turn white by the same logic, when their sand holds quartz or eroded limestone that scatters sunlight, and tropical white sand often carries calcium carbonate from seashells ground fine by the waves. Snow is a mixture of air and tiny ice crystals, and when white sunlight enters it, very little of the spectrum is absorbed. Almost all the light is reflected or scattered by air and water molecules, so the snow appears the color of sunlight. Sometimes light bounces around inside the crystals before scattering, which makes snow seem to sparkle. Glaciers behave differently, because their ice is pressed tightly together with little air, so more red light is absorbed and the scattered light turns bluish. Clouds work like snow, composed of water droplets or ice crystals mixed with air, scattering most light back as white, though shadows from clouds above can make them look gray. Mountains carry the color in their names. Mauna Kea means white mountain in Hawaiian, Mont Blanc means white mountain in French, and the Changbai Mountains, meaning perpetually white mountains, mark the border between China and Korea.

• 6. Purity And Mourning

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  The pope has worn white regularly since 1566, when Pope Pius V, a member of the Dominican Order, began the practice, and white is the color of that order. Earlier popes wore white only occasionally in the Middle Ages and usually wore red. Within the church hierarchy, lighter colors marked higher rank, with ordinary priests in black, bishops in violet, cardinals in red, and only the pope in white outside a church. The early Christian church inherited from Rome the idea of white as purity, sacrifice, and virtue, making it the color worn during Mass and by the monks of the Cistercian Order. In the Church of Jesus Christ of Latter-day Saints, white marks purity and cleanliness in baptism and temple ceremonies, where all participants wear white to signal unity and equality before God. Islam ties white to pilgrimage, where men on the Hajj wear Ihram clothing of two un-hemmed white sheets, the riḍā draped over the torso and the izār secured by a belt, typically during Dhu al-Hijjah, the last month of the Islamic calendar. White also carried political weight in Islam, from the white banner tradition ascribes to the Quraysh, the tribe of Muhammad, to the dynastic white of the Umayyads and the Shi'ite Fatimids, who chose it against the black of the Sunni Abbasid Caliphate. Yet the same color means death across much of Asia. In China, Korea, and other Asian countries, the whitish color of undyed linen is worn at funerals, and in traditional China small sacks of quicklime, one for each year of the deceased's life, are placed around the body. In ancient Egypt white also meant death, standing for the lifeless desert, while black, the color of the Nile's fertile mud, gave the country its name Kemet, the black land.

• 7. Politics And Surrender

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  The White movement formed against the Bolsheviks during the Russian Civil War that followed the Russian Revolution of 1917, a coalition of monarchists, nationalists, and liberals defeated in 1921 to 1922, after which many members emigrated to Europe. The color's link to monarchy runs deeper, originating in the white flag of the Bourbon dynasty of France, which became the banner of royalist rebellions against the French Revolution, as in the Revolt in the Vendée. A parallel war between reds and whites broke out during the Civil War in Finland in the same period. Not all white politics meant restoration. In Iran, the White Revolution was a series of social and political reforms launched in 1963 by the last Shah before his downfall. White also stands for peace and passive resistance, carried by the white ribbon worn against violence toward women, and by the White Rose, a non-violent resistance group in Nazi Germany. The white flag has signaled surrender or a request for truce since the 15th century, when multicolored flags and firearms came into common use during the Hundred Years' War between France and England. It was officially recognized as a request to cease hostilities by the Geneva Convention of 1949. The color also marks darker movements, including the Ku Klux Klan, which wore white robes and hoods and murdered black Americans in the Southern United States after the American Civil War.

• 8. The Color Of Dying Stars

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  A white dwarf is a stellar remnant made mostly of electron-degenerate matter, so dense that its mass rivals the Sun's while its volume rivals the Earth's. Its faint glow comes from stored thermal energy alone. Born very hot, a white dwarf has no source of new energy, so it gradually radiates away what it has and cools, its light reddening from a high color temperature over time. Eventually it would reach temperatures too low to emit significant heat or light, becoming a cold black dwarf. But no white dwarf can be older than the age of the universe, roughly 13.8 billion years, so even the oldest still radiate at a few thousand kelvins, and no black dwarfs are thought to exist yet. A different white belongs to the living sky. An A-type main-sequence star, also called an A dwarf, burns hydrogen and shows strong hydrogen Balmer absorption lines, with masses from 1.4 to 2.1 times the Sun's and surface temperatures between 7600 and 11500 K. Closer to home, white animals turn the color into survival. Some use white as winter camouflage, while penguins are countershaded with white bellies, hiding against the light from below as they swim.