Purple and blue are colors that have captivated humans for centuries. These cool hues evoke feelings of tranquility, spirituality, luxury, and creativity. But what makes purple and blue look the way they do? The answer lies in pigments – the ingredients that give color to various materials. By exploring the history, science, and use of purple and blue pigments, we can better understand what gives these colors their distinctive appeal.
The History of Purple
For much of human history, purple has been associated with royalty, nobility, and prestige. This is because in antiquity, purple dye was extremely rare and labor-intensive to produce. The rarity and cost meant that only the wealthiest individuals could afford purple garments.
The signature purple shade came from a pigment called Tyrian purple, which was produced from a type of sea snail called the spiny dye-murex. Found in the Mediterranean Sea, these snails were laboriously harvested, producing only minuscule amounts of the precious dye. It took approximately 10,000 snails to yield just 1 gram of Tyrian purple pigment. After being extracted and exposed to sunlight, the pigment would turn a beautiful violet-purple hue.
Because of the tremendous difficulty of procuring Tyrian purple, it became associated with prestige and royalty among the ancient Phoenicians, Greeks, and Romans. Roman emperors and senators wore special purple togas to denote their high office. The Byzantine emperors of Constantinople continued the royal purple tradition. Meanwhile in Mesoamerica, the elite of the Maya and Aztec cultures produced a similar precious purple dye from local snails.
After the fall of Constantinople in 1453, the means of producing Tyrian purple were eventually lost. It would not be until the 19th century that modern chemistry allowed cheaper synthetic versions of the pigment to be produced. This allowed purple garments to become more widely accessible beyond royalty.
The Science of Purple Pigments
What makes Tyrian purple and other purple hues have their characteristic color? Pigments obtain their color based on their specific chemical composition, which determines how they absorb and reflect light.
Tyrian purple consists primarily of a bromine-containing compound called 6,6′-dibromoindigo. This chemical forms after a series of chemical reactions, beginning with compounds extracted from the murex sea snails. The presence of bromine in the molecule causes it to absorb yellow and green light from the visible light spectrum. The reflected light appears purple to the human eye.
Modern synthetic purple pigments work similarly. Manganese phosphate, cobalt violet, and dioxazine purple all contain elements that selectively absorb parts of the light spectrum, leading the pigments to reflect violet and purple hues.
Here is an overview of some common purple pigments and their chemical compositions:
| Pigment | Chemical Composition |
|---|---|
| Tyrian or Royal Purple | 6,6′-dibromoindigo |
| Manganese Ammonium Phosphate | (NH4)MnP4 |
| Cobalt Violet | Co3(PO4)2 |
| Dioxazine Purple | C22H14Cl2N4O4 |
Making Purple Paints and Dyes
Purple pigments allow us to color a wide array of materials purple, including paints, dyes, plastics, and cosmetics. Here is an overview of how purple pigments are used in paints and dyes:
Paints – Purple oil or acrylic paint contains fine purple pigment particles suspended in an oil or acrylic binder. Common purple pigments used include manganese phosphate, quinacridone, and dioxazine. The pigment provides color while the binder allows the paint to adhere to surfaces.
Dyes – Purple fabric dyes contain purple pigment molecules that bind to fabric fibers to impart color. Common purple dyes include methyl violet and mauveine. These synthetic dyes replaced tyrian purple for dying fabrics. The dye molecules form very strong bonds with fabrics, allowing the purple color to remain even after washing.
Understanding how purple paints and dyes obtain their color can help artists and designers select the right materials for their needs. Synthetic pigments allow vibrant, affordable purple colors to be produced at large scale for paints, textiles, plastics and more.
The Science of Blue Pigments
Like purple, blue is a color with a rich history and science behind its striking hues. Blue often represents tranquility, stability, wisdom, and trust. But what makes blue pigments blue from a chemical perspective?
One of the earliest and most precious blue pigments was ultramarine, made from the gemstone lapis lazuli. Lapis crystals contain sulfur impurities that absorb light and reflect vibrant blue wavelengths. However, lapis lazuli was rare and expensive. It was reserved for elite paints and manuscripts.
Prussian blue was an important early synthetic blue pigment, accidentally discovered in 1704. It contains iron cyanide complexes that selectively absorb parts of the visible spectrum, resulting in deep blue color.
Phthalocyanine blue and indanthrone blue are examples of intensely colored organic blue pigments discovered in the 20th century and widely used today. Their complex aromatic molecular structures absorb orange and red light, reflecting blue.
Here is an overview of some key blue pigments and their chemical compositions:
| Pigment | Chemical Composition |
|---|---|
| Ultramarine | Na8-10Al6Si6O24S2-4 |
| Prussian Blue | Fe7(CN)18 |
| Phthalocyanine Blue | C32H16CuN8 |
| Indanthrone Blue | C16H10N2O2 |
Making Blue Paints and Dyes
Understanding blue pigments allows us to use them for a wide range of blue-colored materials:
Paints – In oil or acrylic paints, blue pigment particles are dispersed in an oil or acrylic vehicle. Ultramarine, phthalocyanine, and Prussian blue are commonly used. The pigments absorb certain light wavelengths, causing the paint to reflect blue.
Dyes – Blue textile dyes work by forming strong bonds with fabric molecules. Indigo dye, derived from plants, has been used since antiquity to color fabrics blue. Modern synthetic blue dyes include phthalocyanine compounds similar to blue pigments.
From vivid navy to pale sky blue, blue pigments and dyes allow us to color our world in cool, calming shades. Understanding the chemistry behind these pigments allows paint, dye, and material producers to create products with optimized blue color.
Conclusion
The distinctive colors of purple and blue originate from pigments – compounds selectively absorbing light to reflect alluring violet and blue wavelengths.Tracing the histories of Tyrian purple, lapis lazuli, and synthetic pigments reveals an evolution in chemistry that provided artists and craftspeople with a vibrant palette. Manipulating the molecular compositions of pigments allows new shades of purple and blue to be produced. With science enhancing art, these regal, contemplative colors will continue reflecting the beauty and wonder of the natural world.
