Blue

Blue is one of the three primary colours used in both the RGB (additive) colour model and the RYB colour model. It appears between violet and cyan on the spectrum of visible light. We see blue in the clear daytime sky and the deep sea because of an optical effect called Rayleigh scattering.

Blue has been important in art and decoration for thousands of years. Ancient Egyptians used the stone lapis lazuli to make beautiful jewellery. During the Renaissance, artists used lapis lazuli to create a precious blue pigment called ultramarine. In China, artists used cobalt blue for blue and white porcelain. Later, blue became popular in European cathedrals and everyday clothing.

Today, blue is a favourite colour for many people around the world. It is often linked with feelings of harmony, confidence, calmness, and knowledge. Blue is also the colour of the flags of the United Nations and the European Union.

Etymology and linguistics

The word blue in English today comes from older words in different languages. It started with words like bleu in Old French, which came from Germanic roots meaning something like "shimmering."

Some languages have different words for light blue and dark blue. For example, in Russian, light blue is called goluboy and dark blue is siniy. In other languages, like Japanese and Vietnamese, the same word is used for both blue and green. In Japanese, the word ao can mean blue or what we might call green, like the color of traffic lights that mean "go." This shows that not all languages separate blue and green the way English does.

Research shows that when languages develop color words, they usually start with black and white, then add red, and blue is often one of the last colors to get its own name. This usually happens when people can reliably make blue dyes or paints.

Optics and colour theory

The word blue describes the colour we see when we look at light with a certain wavelength, between about 450 and 495 tiny units called nanometres. Blues with shorter wavelengths look more like violet, while those with longer wavelengths look more like cyan. The purest blues sit in the middle, around 470 nanometres.

A scientist named Isaac Newton counted blue as one of the seven colours in the rainbow. He chose seven colours because he thought they matched the notes in music. In old art, blue was one of the three main colours — along with red and yellow — that artists mixed to make new colours. These three colours can make many others: red and yellow make orange, yellow and blue make green, and blue and red make purple. Mixing all three makes a dark brown colour.

LED

In 1993, a scientist named Shuji Nakamura made bright blue lights using a special technology called LEDs. Two other scientists, Isamu Akasaki and Hiroshi Amano, worked on similar ideas. Their work helped change how we use lighting today.

Lasers

Blue lasers became common for everyday use around 2010. Before that, making blue laser light was expensive and hard, but new technology made them easier to find and use. Scientists still use special blue lasers for important work like studying cells and measuring tiny movements.

Shades and variations

Main article: Shades of blue

Blue is the colour of light between violet and cyan on the visible spectrum. Different blues include indigo and ultramarine, which are close to violet; pure blue without any other colours mixed in; and Azure, a lighter blue like the colour of the sky. Cyan is halfway between blue and green, and there are other blue-greens such as turquoise, teal, and aquamarine.

Blue can be darker or lighter. Darker blues contain black or grey, such as ultramarine, cobalt blue, navy blue, and Prussian blue. Lighter blues contain white and include sky blue, azure, and Egyptian blue (see the List of colours for more).

As a structural colour

Further information: Structural colouration

In nature, many blue colours come from how light bounces off surfaces. When light reflects off two or more thin layers, it can combine in ways that make certain colours appear. This creates beautiful blue colours without using any colourings.

Colourants

Main article: Colourants

Some famous blue colourants include Egyptian blue, Cobalt blue, Copper phthalocyanine, YInMn blue, and Prussian blue. Prussian blue, shown in chemical form as Fe^III₄[Fe^II([CN])₆]₃, is the blue colour found in old blueprints.

Artificial blues

Egyptian blue was the first blue colour made by people, created in ancient Egypt thousands of years ago. Before the 1700s, most blue colours came from a special stone called lapis lazuli. In 1709, a new blue called Prussian blue was discovered by a German scientist. It became very popular for paintings and wallpaper. Later, new blue colours like cobalt blue were made, and in the 1800s, people learned how to make a blue colour called ultramarine in labs instead of mining it from stones.

In 1878, a company made a blue colour called indigo, which is now used to colour blue jeans. Since then, many new blue dyes have been created that stay bright even when washed or left in the sun.

Dyes for textiles and food

For many years, people used plants like woad and true indigo to colour clothes blue. Today, almost all blue colour used for jeans comes from a lab-made version of indigo. Blue colours for food include a special dye called Brilliant blue FCF, used in some candies. Some blue foods, like blue raspberry-flavoured treats, get their colour from a dye called Blue No. 1.

Pigments for painting and glass

Blue colours used in paintings were often made from minerals like lapis lazuli. Today, artists use lab-made blue colours like cerulean blue and Prussian blue. In glass, a metal called cobalt gives a blue colour. This is used in special glass windows and old Chinese pottery.

Inks

A colour called methyl blue is commonly used in pens. Blueprinting, a way to make copies of technical drawings, uses Prussian blue.

Inorganic compounds

Some metals can create blue colours when mixed with other materials. For example, cobalt is used to make deep blue glass and pottery, and copper can make blue solutions used in some products.

In nature

Sky and sea

Further information: Rayleigh scattering and Why is the sky blue?

When sunlight passes through the air, blue light scatters more, making the sky look blue. This is called Rayleigh scattering. The sea looks blue for a similar reason: water absorbs red light and scatters blue light, making the water appear blue. The deeper you go, the darker the blue becomes.

The colour of the sea can also change based on the sky, tiny particles in the water, plants like algae, or bits of dirt that make the water look brown.

Minerals

Some of the most beautiful gems are blue, like sapphire and tanzanite. Copper can create blue colours in minerals. Azurite is a blue mineral that was used long ago but fades in dry conditions. Lapis lazuli, mined for thousands of years, was used for jewellery and as a valuable blue pigment in art.

Plants and fungi

Many plants have blue flowers, like morning glory and blue delphinium. Some blue colours in plants come from special pigments, while others are created by structures in the cells. One amazing blue colour is found in the berries of a plant called Pollia condensata, where spiral structures make the blue colour.

Animals

Blue colours in animals are less common. Some butterflies and fish have blue pigments, but more often, blue looks come from how light bends around tiny structures. Birds like blue jays and indigo buntings, and butterflies like the morpho butterfly, show this kind of blue.

Eyes

Main article: Eye colour § Blue

Blue eyes don’t contain blue pigment. The colour comes from how light scatters in the eye’s iris. People with blue eyes have less dark pigment, which allows more blue light to reflect out. Blue eyes are most common in places like Ireland, the Baltic Sea area, and Northern Europe, and are also found in parts of Western Asia. In the United States, about 16.6% of people have blue eyes.

History

In the ancient world

Lapis lazuli was mined as early as the 7th millennium BC in places like Sar-i Sang, Shortugai, and Badakhshan province in northeast Afghanistan. Artefacts made from lapis lazuli dating back to 7570 BC have been found at Bhirrana, an early site of the Indus Valley civilisation. Lapis was highly valued and used in important items like the funeral mask of Tutankhamun.

Blue was not commonly used in ancient art or writing. The Ancient Greeks described the sea as green or brown, and blue wasn't used in cave paintings from the Upper Paleolithic period. Blue dyes and pigments were hard to make, which made them rare and valuable. The earliest blue dye came from plants like woad in Europe and indigo in Asia and Africa. Minerals like lapis lazuli and azurite were used to make blue pigments. The Romans used blue in their art and had many words to describe different shades of blue.

In the Middle Ages

During the early Middle Ages in Europe, blue wasn't used much in art. This changed around 1130–1140 in Paris when Abbe Suger rebuilt the Saint Denis Basilica with stained glass windows coloured with cobalt blue. This created a special blue light inside the church, which became famous. The Roman Catholic Church later decided that painters should show the Virgin Mary in blue, which made blue a symbol of holiness and virtue. Blue also became a royal colour, used in the coats of arms of the kings of France.

Renaissance through 18th century

Blue became more common in art during the Renaissance. Artists used blue and red together to create depth and harmony in their paintings. Ultramarine, a very expensive blue made from lapis lazuli, was highly prized by wealthy patrons. Blue and white pottery began in China during the 14th century, using cobalt blue patterns. This style was later copied by craftsmen in Delft and Staffordshire.

19th-20th century

In the early 19th century, the modern blue business suit began with Beau Brummell. Blue jeans were invented in 1853 by Jacob W. Davis using metal rivets to strengthen denim work clothing. Artists in the 19th and 20th centuries, such as Henri Matisse and Pablo Picasso, used blue to express emotions and create moods in their paintings.

In society and culture

Blue is a color often seen in uniforms. For example, navy blue comes from the uniforms of Royal Navy officers. In the past, blue was also used in military uniforms, like those of the Prussian army and the US Army.

Blue is also linked to gender, often representing males, especially in clothing and symbols since the mid-20th century.

In religion, blue holds special meaning. In Hinduism, gods like Krishna and Rama are shown with blue skin. In Christianity, blue is linked to the Virgin Mary, often shown in blue clothing in paintings. Blue also appears in Sikh traditions, where warriors wear blue, and temples display blue banners.

In sports, many teams wear blue, like the French national football team, known as "Les Bleus." Blue is also common in baseball, basketball, and hockey uniforms.

In politics, blue is used in flags like those of the United Nations and the European Union. It is often the color for conservative parties in many countries, though in places like the United States, blue represents the Democratic Party.