Purple is a color that has fascinated humans throughout history. In ancient times, purple dye was highly prized and often reserved for royalty. The rarity and expense of purple fabric gave it a mystical and luxurious appeal. So what gives this color its unique properties? The origin of purple’s distinctive hue lies in the natural world.
Purple coloration arises from two main sources in nature – minerals and living organisms. On the mineral side, various rocks, gems and ores can display purple, violet or lavender shades due to their particular mineral compositions and molecular structures. But perhaps the most striking and intensely vibrant purples are produced through biology – by specific pigments found in certain flowers, fruits, animals and microbes.
Over thousands of years, humans have learned to extract and concentrate these natural purple pigments to dye clothing, textiles, artwork and more. So the precious purple fabric found draped on kings and emperors of antiquity started its life in a humble lichen, snail or plant.
In this article, we’ll explore some of the key biological and geological sources of natural purple, and how these raw materials are transformed into vivid pigments and dyes. We’ll also look at the unique visual effects and cultural symbolism carried by the color purple itself.
What Minerals or Rocks are Purple?
In the geological world, a number of minerals and rocks exhibit purple, violet or lavender hues, including:
- Lepidolite – a lithium-bearing mica mineral ranging from pink to deep lavender.
- Fluorite – a mineral that can display many colors, including purple, blue and green varieties.
- Amethyst – a popular purple quartz gemstone.
- Sugilite – an obscure mineral found in vivid purple rocks.
- Charoite – a purple silicate mineral used as an ornamental stone.
- Purpurite – a rare, fragile purple phosphate mineral.
- Hematite – an iron oxide mineral that can have metallic purple hues.
The purple color in these geological materials arises from their unique mineral structures and elemental compositions. For example, trace amounts of manganese, iron, cobalt and other transition metals can contribute violet or purple wavelengths to a mineral’s light absorption. Complex crystal structures can also scatter light to give a purple sheen.
While mineral purples are striking, they tend to be quite diffuse and pale compared to the rich, saturated hues produced by biological pigments. Next we’ll look at some key purple compounds from the living world.
Purple Pigments in Nature
Plants, animals and microbes synthesize a diverse array of purple and violet pigments as part of their normal metabolism, physiology and ecology. Here are some of the major biological sources of purple color in nature:
Anthocyanins
Anthocyanins are water-soluble plant pigments that appear red, purple or blue depending on pH. They are found in the cells of many flowers (e.g. orchids, pansies, lilies), fruits (e.g. grapes, berries, plums), leaves (e.g. purple cabbages and corn), roots (e.g. radishes, carrots) and other plant tissues. Over 600 anthocyanins have been identified in nature so far.
Betalains
Like anthocyanins, betalains are a class of purple/red pigments produced by plants for coloring flowers and fruits. Betalains are found in beets, prickly pear cacti and amaranth plants. They are water-soluble and pH-sensitive like anthocyanins, but have a distinct molecular structure.
Indigo
The tropical indigo plant produces the precursor molecule indican, which must be chemically processed to generate the sky-blue indigo dye. Indigo has been used as a textile dye across the world for centuries. It played a particularly prominent role in the 18th/19th century plantation economies of colonial North America.
Purple Carotenoids
Carotenoids are the orange/red/yellow pigments produced by plants and photosynthetic bacteria. A few rare variants are purple, like the siphonaxanthin found in green algae. Sea sponges and other coral reef dwellers can also accumulate peculiar purple carotenoids in their bodies.
Murex Snail Pigments
Some species of predatory sea snails in the family Muricidae secretes a purple fluid as part of their venom and reproductive cycle. This snail mucus contains a mixture of unique brominated indole compounds called Murex dyes or Tyrian purple. Murex dye was laboriously extracted by ancient cultures to color royal garments.
Lichen Pigments
Lichens are symbiotic organisms composed of a fungus paired with a photosynthetic partner (either a cyanobacterium or alga). Lichens generate a variety of pigments, including intensely colored anthraquinone compounds. These lightly purple lichen pigments were historically used for dyeing wool and other textiles.
Purple Bacteria Pigments
Many species of photosynthetic bacteria can synthesize vivid purple pigments called bacteriopurpurins. These compounds help the bacteria harvest light energy and carry out photosynthesis in aquatic environments. Extracts from these “purple bacteria” have been used as a natural food coloring.
Colorfast Purple Dyes
While purple pigments are abundant in nature, they suffer from a major drawback – they readily wash out and fade when exposed to water, soap, sunlight and other conditions. So how were more colorfast purple dyes created from these fragile natural pigments?
The key breakthrough was discovering certain “mordant” chemicals that act to fix fugitive purple dyes so they bind permanently to textile fibers. Here are some examples of how mordant dyes produced colorfast purple fabrics:
- Murex purple – Salt and iron solutions help fix the pigment to woven wool or silk.
- Lichen purple – Treating wool with ferrous sulfate or urine can bind the dye to fiber strands.
- Indigo – Vat dyeing removes indigo’s oxygen atoms so it penetrates fibers and binds strongly.
- Plant anthocyanins – Alum and tin mordants allow these delicate pigments to dye fabrics.
With these mordanting techniques, dyers could transform the beautiful but delicate purple pigments from nature into stable dyes for valuable textiles. The rarity and cost of some purple dyes meant they were reserved for prestigious or sacred artifacts and garments.
The Symbolism and Meaning of Purple
What is it about the color purple that carries such mystical allure and associations with luxury? There are a few factors:
- The rarity and cost of some purple dyes connected them to royalty and wealth.
- Purple’s mixture of warm red tones and cool blue is visually striking and contrasting.
- Purple is tied mathematically to the “golden ratio” used in art and architecture.
- Purple has spiritual meaning in multiple religions, symbolizing wisdom, mystery and truth.
So whether it stems from the regal robes of emperors, the glow of amethyst gemstones, or the contemplative colors of twilight, purple has woven its way into human culture, psychology and our fundamental perception of color itself.
Conclusion
In summary, the signature purple color arises from a diverse array of pigments produced in minerals and living organisms. While pale lavenders exist in the mineral world, the richest and most vivid hues of purple originate from plants, lichens, fungi, sea snails and bacteria via their evolved biochemistry. After being discovered and concentrated by dye masters and artisans, these fragile biological pigments could be transformed into precious, royal purple fabrics using mordant dyes. The cultural legacy of purple continues to this day, with these rare hues symbolizing luxury, creativity, spirituality and the mysteries of nature.
