Blue
Sunlight passes through the atmosphere and scatters blue wavelengths more widely than other colors. This optical effect is called Rayleigh scattering after Lord Rayleigh. Albert Einstein confirmed this phenomenon in 1911. The sky appears blue because oxygen and nitrogen molecules scatter short-wavelength light toward our eyes. The sea also looks blue for largely the same reason. Water absorbs longer red wavelengths while reflecting and scattering blue light back to the viewer. In open seas, only about one percent of light penetrates to a depth of two hundred meters. Distant mountains often appear blue due to atmospheric perspective. The farther an object sits from the viewer, the less contrast exists between it and the background color. That background usually remains blue. Blue light scatters more than other wavelengths by gases in the atmosphere. This creates what scientists call our blue planet.
Lapis lazuli was mined in the Sar-i Sang mines as early as the seventh millennium BC. These deposits lie in Badakhshan province in northeast Afghanistan. Artifacts dated to 7570 BC have been found at Bhirrana, the oldest site of the Indus Valley civilization. Lapis beads appeared in Neolithic burials across the Caucasus and even reached Mauritania. Ancient Egyptians used lapis lazuli for jewelry and ornamentation. They created Egyptian blue in the third millennium BC by heating pulverized sand, copper, and natron. This pigment protected the dead in their afterlife within tomb paintings. Chinese artists began using cobalt blue for fine porcelain in the eighth century. European painters relied on woad dye until indigo arrived from America. Prussian blue emerged in 1709 when Johann Jacob Diesbach discovered it while experimenting with dried blood and iron sulfides. By 1710 French painter Antoine Watteau used this new pigment. It became popular for wallpaper manufacturing and later for French impressionist painters. The Societe pour l'Encouragement d'Industrie offered a prize in 1824 for artificial ultramarine. Jean Baptiste Guimet won that prize in 1826 but refused to reveal his formula. Christian Gmelin published the process in 1828. German chemists synthesized indigo in 1878. That product rapidly replaced natural indigo farms.
Abbe Suger rebuilt the Saint Denis Basilica between 1130 and 1140 in Paris. He installed stained glass windows colored with cobalt to create bluish violet light. The church became known as the Blue Church of Christendom. In the twelfth century, the Roman Catholic Church dictated that Italian painters dress Virgin Mary in blue. This decree linked the color to holiness, humility, and virtue. Paintings of King Arthur began showing him dressed in blue during medieval times. The coat of arms of French kings featured an azure shield sprinkled with golden fleur-de-lis. Blue became the royal color by the fourteenth century. Pope Gregory I ordered all religious paintings to clearly tell stories to viewers. If Mary stood alone in an image, her costume used the finest blue pigment available. If she appeared with Christ, artists used less expensive pigments to avoid outshining him. Jewish tradition commanded Israelites to weave twisted threads of blue into garment fringes. Maimonides claimed this blue matched the clear noonday sky. Rashi described it as the evening sky color. Hindu gods like Vishnu appear with blue skin to symbolize water connection. Krishna and Rama are avatars of Vishnu depicted with blue skin. Shiva is called Nīlakañtha or blue-throated for swallowing poison.
Shuji Nakamura demonstrated high-brightness blue LEDs at Nichia Corporation in 1993. Isamu Akasaki and Hiroshi Amano worked on parallel developments at Nagoya University. Their work revolutionized LED lighting technology globally. Nakamura received the Millennium Technology Prize in 2006 for his invention. Akasaki, Amano, and Nakamura shared the Nobel Prize in Physics in 2014. Lasers emitting blue wavelengths became widely available to the public in 2010. Inexpensive high-powered laser diode technology released between 445 and 447 nanometers made these devices accessible. Previously scientists accessed blue wavelengths only through DPSS systems which were expensive and inefficient. Blue gas lasers remain common for holography and DNA sequencing applications. The invention changed how humanity produces light worldwide. This technological shift enabled energy-efficient lighting solutions across industries. Scientists use blue wavelengths for optogenetics and Raman spectroscopy today.
Blue represents males beginning as a trend in the mid-nineteenth century. Gendered associations with blue became widespread from the 1950s onward. The color associated with males after World War II ended. Surveys show blue is the favorite color of both men and women in the United States and Europe. Recent surveys found similar results in China, Malaysia, and Indonesia. Russian, Mongolian, and Irish languages lack single words for blue. They distinguish light blue and dark blue with different terms. Japanese uses one word for colors English speakers call green or blue. Traffic signals meaning go appear blue in Japan. Lakota Sioux use the same word for blue and green without distinction. Linguistic research indicates languages develop color names individually over time. Black and white typically emerge first followed by red. Blue usually appears last when cultures can manufacture reliable pigments. In Estonia, ninety-nine percent of people have blue eyes. Only eight percent of Denmark's population had brown eyes in 1978. About seventy-five percent of Germans possess blue eyes today. One out of every six Americans has blue eyes as of 2006. Males are three to five percent more likely than females to have blue eyes.
Frederick William I of Prussia chose Prussian blue for military uniforms in the seventeenth century. He selected this local crop-based color instead of indigo from England. The German army wore these uniforms until World War I ended. Bavarian soldiers wore sky-blue exceptions during that period. The Royal Navy adopted marine blue for officer uniforms in 1748. George Washington selected blue and buff for militia field uniforms. Blue remained the US Army dress uniform color until 1902. Metropolitan Police officers in the United Kingdom adopted navy blue uniforms in the nineteenth century. Similar traditions emerged in France and Austria around the same time. New York City Police Department officers also received navy blue uniforms then. Conservative parties often use blue contrasting with left-wing red associations. The Conservative Party UK and Liberal Party Australia both employ blue branding. The Democratic Party uses blue while Republicans use red in American politics. South Korea follows this model with Democrats using blue and People Power Party using red. The United Nations chose blue as its flag color because it represents harmony. NATO flags also feature blue for similar reasons. Blue jeans invented by Jacob W. Davis in 1853 became worker clothing. Levi Strauss funded the invention using metal rivets to strengthen denim.
Common questions
What is the scientific explanation for why the sky appears blue?
The sky appears blue because oxygen and nitrogen molecules scatter short-wavelength light toward our eyes. This optical effect is called Rayleigh scattering after Lord Rayleigh. Albert Einstein confirmed this phenomenon in 1911.
When was Prussian blue discovered and who invented it?
Prussian blue emerged in 1709 when Johann Jacob Diesbach discovered it while experimenting with dried blood and iron sulfides. By 1710 French painter Antoine Watteau used this new pigment. It became popular for wallpaper manufacturing and later for French impressionist painters.
Who won the Nobel Prize in Physics for developing high-brightness blue LEDs?
Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura shared the Nobel Prize in Physics in 2014. Shuji Nakamura demonstrated high-brightness blue LEDs at Nichia Corporation in 1993. Isamu Akasaki and Hiroshi Amano worked on parallel developments at Nagoya University.
Why did the Roman Catholic Church dictate that Italian painters dress Virgin Mary in blue?
In the twelfth century, the Roman Catholic Church dictated that Italian painters dress Virgin Mary in blue to link the color to holiness, humility, and virtue. Pope Gregory I ordered all religious paintings to clearly tell stories to viewers. If Mary stood alone in an image, her costume used the finest blue pigment available.
When did gendered associations with blue become widespread for males?
Blue represents males beginning as a trend in the mid-nineteenth century. Gendered associations with blue became widespread from the 1950s onward. The color associated with males after World War II ended.