Indigo is one of the colors of the visible light spectrum that can be seen in a rainbow. It sits between blue and violet at a wavelength of around 445-420 nanometers. Isaac Newton originally identified indigo as one of the seven colors of the rainbow in his color wheel, along with red, orange, yellow, green, blue, and violet.
The Origins of Indigo
The name “indigo” comes from the Greek word “indikon” meaning “blue dye from India.” This is because the dye used to produce the color indigo originally came from the indigofera tinctoria plant native to India. Indigo dye has been used for centuries throughout Africa, Asia, and India to dye fabrics a deep blue color. It was one of the most prized dyes in the ancient world.
The cultivation of indigo spread to the Americas in the 17th century. El Salvador, Guatemala, Jamaica and Mexico became major indigo producers. Enslaved people were forced to work on indigo plantations throughout Central America and the Caribbean. By the 19th century, synthetic indigo dye was developed and replaced natural indigo as the main source of indigo dye.
Indigo as a Spectral Color
When white light passes through a prism, it separates into the visible spectrum of colors from red to violet. Isaac Newton was the first to systematically study the visible spectrum in the 17th century. He identified seven main colors – red, orange, yellow, green, blue, indigo, and violet.
Modern scientists have found that the human eye has receptors for three primary colors – red, green and blue. All other colors are seen by the eye as combinations of these three. Indigo stimuli activate both the blue and violet color receptors in the eye to produce the sensation of indigo.
Indigo sits at a wavelength of around 445-420 nanometers on the visible spectrum. It lies between blue (at 450–495 nm) and violet (at 380–450 nm). This means indigo light has a higher frequency and shorter wavelength than blue, but a lower frequency and longer wavelength than violet.
Properties of Indigo
Here are some key properties of the color indigo:
- Wavelength range: 445–420 nm
- Frequency: 668–714 THz
- Hex triplet: #4B0082
- sRGBB (r, g, b): (75, 0, 130)
- CMYK (c, m, y, k): (58, 100, 0, 49)
- Complementary color: Yellow
Indigo is a deep and rich color. It sits between the primary colors blue and violet, so it has some of the qualities of both. To the eye, indigo appears as a dark blue with some violet character.
Indigo Dye
The dye used to color fabrics indigo comes from the indigofera tinctoria plant. Other plant sources of indigo dye include dyer’s knotweed and the woad plant. To create indigo dye:
- Leaves from the indigo plants are soaked and fermented to produce indican.
- The indican is oxidized to form indoxyl.
- The indoxyl is transformed into insoluble indigo.
- The indigo solid is separated from the liquid and pressed into cakes or powder.
The indigo cakes or powder are then dissolved in vats of water for dyeing. When cloth is dipped into the indigo dye bath, the indigo adheres to the cloth fibers. When exposed to air, the indigo on the cloth undergoes oxidation and turns from yellow-green to the familiar blue color.
Uses of Indigo
Here are some of the main uses of indigo throughout history:
- Dyeing textiles – indigo has been used to dye fabrics blue for centuries
- Pigments and paints – indigo pigments are used in oil paints and watercolors
- Food coloring – indigo dye was once used to color food blue but this has been banned in many countries
- Therapeutics – historically used in traditional Chinese medicine and Ayurveda
- Industrial applications – used in printing inks and protective coatings
Today, indigo is most commonly associated with denim fabric and blue jeans. The distinctive blue color of denim comes from dyeing the warp threads with indigo while leaving the weft threads white.
Indigo in Culture and History
Indigo has played an important role in many cultures and civilizations throughout history:
- India – indigo was one of the most valuable trade commodities shipped from India to Europe from the 15th-19th centuries
- Africa – Yoruba people in West Africa used indigo dye for traditional textiles
- China – indigo was one of the original Chinese dyes used for textile coloring
- Japan – indigo dye was used to create traditional Japanese blue and white porcelain and prints
- Mesoamerica – Maya and Aztec cultures used indigo as a dye and in rituals
In the 18th-19th centuries, colonial empires forced enslaved people to work on indigo plantations in Central and South America. This led to exploitation and harsh working conditions.
Today, indigo holds importance in New Age movements and alternative spirituality. It is believed to represent intuition, inner vision, and revelation.
Indigo in Nature
While indigo as a spectral color is only found in rainbows, there are some natural examples of indigo found in animals, plants, and minerals:
- Blue jays and bluebirds have indigo coloring in their feathers
- Some varieties of hydrangeas, grapes, and plums have an indigo tint
- Larkspur flower has pigments that appear indigo
- Indigo milk cap mushroom is named for its blue color
- Indigo snake and blue-spotted salamander have indigo tones
- The mineral indicolite is a blue to indigo tourmaline
Indigo vs. Blue
Indigo and blue are often confused for one another. However, indigo is considered to be a distinct color from blue. Here’s how they differ:
| Indigo | Blue |
|---|---|
| Darker, more violet tone | Brighter, pure tone |
| Lower frequency light (420-445nm) | Higher frequency (450-495nm) |
| Named color in Newton’s spectrum | One of the three additive primary colors |
So while indigo sits between violet and blue on the spectrum, it is considered to be its own distinct color based on its unique hue and properties.
Conclusion
Indigo is a deep blue color with a violet tinge that sits between blue and violet on the visible light spectrum. While often confused with basic blue, indigo is considered one of the seven main rainbow colors. The dye has been used for centuries to color fabrics, particularly in India and Central America. Indigo continues to have importance in culture, history, spirituality, and nature.