Cobalt is a chemical element with the symbol Co and atomic number 27. It is found in the Earth’s crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
Cobalt-based blue pigments have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought by alchemists to be due to the known metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were so named because they were poor in known metals, and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.
So in summary, cobalt has been associated with blue pigments and glass for centuries, but its status as an elemental metal was not established until relatively modern times. This leads to an uncertainty around whether to classify it as primarily a blue or purple color. Let’s take a deeper look at the evidence.
Properties of Cobalt that Produce Blue and Purple Colors
Cobalt’s name comes from the German word “kobold”, meaning goblin or evil spirit, a term used by miners for cobalt-bearing ores that hampered the extraction of more desirable metals. This stems from cobalt’s association with blue and purple colors.
Some key properties of cobalt that result in blue and purple colors:
– Cobalt ions have electronic transitions in the visible light spectrum that lend deep blues and purples. Specifically, cobalt(II) ions absorb red and green light, resulting in a strong reflection of blue and purple.
– Cobalt(II) chloride is a famous inorganic blue-purple pigment known as cobalt blue. It has been used as a coloring agent in ceramics and jewelry for thousands of years.
– Cobalt glass, made by adding cobalt compounds to molten glass, has an intense blue color thanks to cobalt(II) ions. This has been done since ancient times to color jewelry and ornaments.
– Cobalt aluminum oxide (CoAl2O4) is a vivid blue-purple pigment widely used in paints, ceramics, enamels, and rubber products.
– Cobalt violet is a purple pigment made from cobalt phosphate that is similar to manganese violet. It is used as an artist’s color and in porcelain and glass.
So in summary, cobalt’s distinct blue and purple colors come from its ions interacting with visible light, and its compounds have lent these hues to pigments and glass for millennia. But is cobalt definitively blue or purple?
Historical Perception of Cobalt as Blue vs Purple
Historically, cobalt has been strongly associated with blue hues rather than purple:
– Ancient Egyptian and Chinese civilizations used cobalt compounds to color blue glass and ceramics thousands of years ago. This set an early precedent for cobalt as a blue colorant.
– In the Middle Ages, cobalt pigments were used extensively for blue paints and glass across Persia, Arabia, and Europe. The color was thought to come from bismuth, not yet realizing it was cobalt.
– The pigment cobalt blue has been used prominently in European paintings since the 19th century, especially by the Impressionists. Its intensity made it a favorite of Vincent Van Gogh.
– When cobalt’s status as an element was discovered in 1735, it was named specifically for its association with blue pigments (from German kobold meaning goblin).
However, purple cobalt compounds and hues were also known:
– Cobalt violet, a popular pigment in the 19th century, lent a purple tone but was less prevalently used than cobalt blue.
– Some minerals with cobalt, like erythrite (cobalt bloom), have a slight purplish cast amidst their blue hues.
– Solutions of cobalt chlorides and other compounds can take on a purple color in certain lighting conditions.
So while cobalt was strongly linked with blue, purple shades were also recognized. But blue has generally been the predominant association.
Modern Scientific Perspective on Cobalt’s Color
From a modern physics perspective, cobalt’s inherent color is technically blue:
– Cobalt has electronic transitions in the visible light spectrum that absorb wavelengths around 550nm, causing it to reflect blue light around 450nm.
– This is seen in cobalt compounds – cobalt blue and cobalt glass have hues close to a pure spectral blue at 450nm.
– Cobalt’s purple hues arise when the blue combines with red wavelengths to produce purple, or from differences in lighting and backgrounds.
– In scientific tests measuring the light spectrums emitted by cobalt compounds, the dominant wavelengths are in the blue region, with weaker signals in the red/purple region.
So scientifically speaking, cobalt’s essential color is blue, arising from its interaction with specific parts of the visible light spectrum. The purple tones are secondary and depend on external factors mixing with the blue.
Cultural Associations Between Cobalt and Color
Some cultural perspectives shed further light on the blue vs purple debate:
– In Chinese culture, cobalt blue glazes and artworks symbolized beauty, elegance, and perfection. This strong cultural link reinforced cobalt as a blue color.
– However, in Central Africa where cobalt mining is concentrated, the indigenous word for cobalt translates more closely to “purple” than blue.
– Psychologically, blue is associated with calmness, stability, and professionalism, while purple evokes mysticism, spirituality, and imagination. Cobalt blue leans more towards the former associations.
– Marketers argue cobalt blue has a unique futuristic yet calming vibe, used by tech and medical companies to convey trust and innovation.
So culturally, cobalt blue fits with symbolic values like calm and trust, though different cultures attach varying names and meanings to its hues. This also emphasizes blue over purple.
Conclusion
In summary, while cobalt can produce soft purples and violets, its primary inherent color is a vivid blue:
– Scientifically, cobalt absorbs greens and reds to reflect predominantly blue light.
– Historically and artistically, cobalt is strongly linked with blue pigments, glass, and compounds dating back thousands of years.
– Culturally, cobalt blue fits with symbolic values like stability and trust in many societies.
However, purple cobalt compounds have their own beauty and uniqueness that should not be overlooked. Ultimately, cobalt’s varied blue and purple shades arise from its innate chemical properties interacting with light, and have enriched human color experiences for millennia.
