Why are there so many ways to make rainbows? From shiny stones to glittering insect wings, from shimmering feathers to glistening shells, from accidental patinas to clever ceramic glazing techniques, iridescence in its various forms has captivated artists and collectors across the ages. Discover how this play of color occurs and see objects in our collections from new angles.
At A Glance
Iridescence in Nature
Iridescence comes from the Greek word for rainbow, iris, and occurs when an object appears to be different colors when viewed from different directions. The color shifts of iridescence can be dramatic, as in precious opals, or subtle, as in a beetle wing, a kingfisher feather, or the corrosion on a glass. Several different phenomena can cause iridescence, and regardless of how it is created, it always remains captivating.
The beautiful emerald color of beetle wings changes depending on the angle from which they are viewed. This iridescent quality protects them from predators. In the small Hindu kingdom of Basohli, located in the Himalayan foothills in the modern state of Himachal Pradesh in northwest India, court artists in the seventeenth century applied shimmering beetle wings to the surface of paintings on paper. Meticulously cut to shape, they were used to simulate emerald jewelry. When viewers lifted the paintings to appreciate their details, the “emeralds” flashed and glittered.
This painting is unique in its depiction of Bhadrakali as a gentle goddess whose form, according to the meditation verse on its reverse, “glows like a topaz.” The glimmering green “emeralds” that she wears are made from iridescent beetle wings pasted onto the painting’s surface. When a viewer lifted the painting, the beetle wings would have flickered, adding movement and drama to the image of the goddess.
Bhadrakali appeared in this specific topaz-colored form to the sage Chyavana, who meditates while gazing at the goddess. Also a physician of great repute, Chyavana is considered the first practitioner of Aryuvedic medicine.
Iridescence in bird feathers usually occurs due to their intricate patterns and the ways in which their structures interact with light. Different colors can be seen from different angles, leading to the amazing array of hues we see in peacock feathers, for example.
In shells, iridescence is caused by thin, alternating layers of different materials and the ways in which they interact with light. The iridescent inner surface of some seashells is called nacre or mother-of-pearl and is made from platelets of the same material that forms the bulk of seashells and coral. Layers of this material, comprised of calcium carbonate and an organic glue, accumulate to trap intrusive debris and to protect the animal’s soft tissue. These thin layers have almost the same thickness as the wavelength of visible light, which is why we see amazing rainbows in them.
The striking contrast between shiny black lacquer and iridescent nacre has become a mainstay of East Asian lacquerware from China, Korea, Japan, and the Ryukyu Kingdom in Japan’s modern-day Okinawa prefecture, whose lacquerware is distinct from other Japanese examples. Intricately cut pieces of shell depict everything from landscapes to decorative patterns, and they cover entire lacquered surfaces of items such as boxes, trays, and tables. The glossy dark surface surrounding the designs in nacre heightens its iridescent glow, enhancing the visual impact of the inlaid design. The color of the nacre can range from white, pink, and purple to greenish-blue in tone. A preference for the nacre-on-black aesthetic prevails in contemporary East Asian lacquer art, as we can see with this tray that would be used for a Japanese tea gathering.
This delicate box in the shape of a hibiscus flower is lavishly decorated with small pieces of metal foil and thin slivers of iridescent shell, or mother-of-pearl, meticulously inlaid into the lacquer surface. A fashion for lacquerware inlaid with foil and shell became popular in the first half of the seventeenth century, but at that time most of the designs consisted of landscapes and figures. In the Kangxi era (1662–1722), a new vogue arose for lacquer decorated with geometric designs executed with great precision, as seen here.
Virtually every inch of this box is embellished. The inside is inlaid with two branches of fruit trees, and the base bears a name seal inlaid in mother-of-pearl as well as images of flowers. The seal reads “Qianli,” which is conventionally believed to be the given name of the craftsman Jiang Qianli. Little historical information has been discovered about this man, so it is possible that the name actually refers to a workshop, not a person. Ultimately, the Qianli seal became synonymous with the technique of delicate, geometric designs inlaid in mother-of-pearl.
The chronological development of mother-of-pearl inlaid lacquer is still imprecisely understood, but this meticulously crafted example fits well into a style associated with the mid-Ming period, beginning in the second half of the fifteenth century. The details of the design bear scrutiny. The artisan’s talent for detailed work is apparent in the pierced garden rock that is incised with two tiny birds near the base and a dragonfly near the top. A recumbent animal, probably a wild hare, is difficult to identify because the inlay for the head is missing. The few extraordinarily brightly colored pieces of shell inlay are later replacements, but most of the original design is intact. For this tray, pieces of mother-of-pearl were set into very slightly recessed beds cut into the lacquer surface. Then a few coats of clear lacquer were applied over the tray to secure the inlay. Any excess was scraped and polished away to create a smooth, level surface in which the sparkling colors of the shell shine against a satiny black background. Lacquer with inlay has a long history that can be traced to the Shang dynasty (ca. 1600–ca. 1050 BC), when some objects were embellished with glittering bits of shell. The creation of complex pictorial designs consisting mostly of pieces of mother-of-pearl did not appear until the Tang dynasty (618–907). This approach to decorating lacquer gradually matured, becoming quite sophisticated in the twelfth century and reaching a new style and high point at the end of the Yuan dynasty (1279–1368) and into the early Ming. In the fourteenth century, artisans began using relatively small, thin pieces of mother-of-pearl (mostly from the inner layer of the haliotis shell), which allowed for greater exploitation of the luster and iridescence of the inlay. Simultaneously, designs became more detailed. This period set a trend followed throughout the Ming.
This box is an outstanding example of lacquerware produced from the Japanese imperial household by the artist Akatsuka Jitoku, whose signature is inscribed inconspicuously on the interior of the lid. The design is executed in flat and low-relief maki-e, a Japanese technique in which gold and silver in the form of fine powder, particles, and leaf are sprinkled and applied over the lacquered surface. Flower petals shaped in low relief from mother-of-pearl are inlaid into the lacquered surface using a technique called raden. The extraordinary quality of the decoration of this box is revealed in such details as the subtly varied iridescent colors ranging from violet to blue-green that are reflected from the inlaid mother-of-pearl shell and the delicate tonalities of the gold decoration.
Patterns inlaid with large pieces of mother-of-pearl shell and scrolls of twisted brass wire decorate this black lacquer box. The decoration represents a Joseon-period (1392–1910) revival of a type of inlaid lacquer made during the Goryeo period (918–1392). An inscription on the inside lid gives a date expressed as part of a sixty-year cycle; possibilities include 1622, 1682, 1742, and 1802.
In contrast to the glimmering mother-of-pearl inlay on lacquer boxes, objects made entirely from mother-of-pearl are both iridescent and translucent. These lustrous plates are constructed of two layers of mother-of-pearl held together using only metal pins and a thin layer of adhesive.
They were made by the artists of Gujarat, a state on the western coast of India. Portuguese traders brought objects like these to Europe for international elites, including Ottoman and Hapsburg emperors. These iridescent plates depict lotuses, an ancient Indian symbol of purity.
Iridescence occurs in stones and minerals as well. In opals, iridescence is caused by small spheres of silica packed closely together. At the right size, the spheres diffract different colors of visible light, causing iridescence.
Frequently found both in nature and in works of art is mica. The mineral mica has a glittery appearance when used in painting due to the plate-like quality of the particles of ground mineral. Mica is a general term to describe minerals made of thin sheets of silicates that reflect light and retain their luster when ground to use in paintings or prints. It can exhibit a range of colors and can also be white or colorless. Mica is perhaps more shimmery than iridescent but still has wondrous interactions with light that have made it a valuable material to use in works of art.
Get closer to a collection of Japanese books decorated with mica with librarian Reiko Yoshimura:
Whether the structures in bird feathers, the thin layers of shell in nacre, or the thin layers of silicates in mica, when the thickness of many materials is close to that of the wavelengths of light, they interfere with the different colors of light and cause iridescence. This can also happen as a material ages. For example, when silver begins to tarnish, the thin layer of tarnish can interact with light and cause rainbow-like iridescence. This layer can also be produced artificially using chemicals to give the surface of a metal object an intentional iridescent patination. When glass or ceramic glazes are wet for long periods of time, whether because they are underwater or they have been buried, the water interacts with the material, forming thin surface layers. The visual appearance changes from transparent colors to an opaque iridescence depending on the surface of the glass or ceramic itself.
While some artists incorporated iridescent materials found in nature, others sought to emulate this dazzling visual effect artificially.
The technique of luster-painted ceramic, which originated in ninth-century Iraq and spread to the rest of the Islamic world and to Europe, is considered one of the most important developments in the history of ceramics. One of the most difficult techniques to control, luster had already been used on seventh-century Egyptian glass before Iraqi potters adapted it to earthenware to lend their low-fired clay surfaces the shimmering effect of precious metals. Vessels or tiles were first fired with an opaque white (tin) glaze, and designs were then painted on the cold surface with a mixture of metal oxides, sulfur, and other materials. During a second firing, oxygen was drawn out of the metallic oxides, leaving behind a shiny film. This complex ceramic tradition spread from Iraq, Egypt, and Syria to Iran in the late eleventh century, where it reached new levels of technical and artistic sophistication during the Seljuq dynasty (1038–1194). The principal city associated with this technique was Kashan in central Iran, which also gave its name to the Persian term for tile, kashi. Adapted to utilitarian vessels, such as plates, bowls, and jugs, as well as tiles destined for both religious and secular structures, Persian lusterware often combined spontaneous cursive writing, usually poetry, with lively figural scenes.
In China and Japan, this artistic interest in creating iridescence is especially apparent in ceramics that were used for drinking tea. For example, Jian ware bowls from the Jian kilns in Fujian, China, are coated in iron oxide–rich feldspathic glazes that create a microcrystalline structure when fired in the kiln. The resulting lustrous glazes exhibit a variety of patterns whose appearance has been likened to oil spots or hare’s fur. The kilns produced tea bowls almost exclusively in the eleventh and twelfth centuries. Several factors contributed to the rise in popularity of Jian ware bowls in the middle of the Song dynasty (960–1279). The most important of these factors was the practice of tea drinking. In the Song period, tea was made from finely ground tea powder. Powdered tea was placed in a bowl, which was filled with hot water and whisked to a white froth with a bamboo whisk. The foamy tea shows best against black glaze. While these tea bowls eventually fell out of fashion in China, they traveled to Japan where they became prized vessels for preparing powdered green tea, or matcha.
Beginning in the sixteenth century, a new style of hand-carved, low-fired ceramics developed in Japan and became popular as tea bowls. Called Raku ware, these bowls were finished with the addition of combustible materials such as straw or leaves, which create a reduction atmosphere that causes the glaze to interact with carbon in the atmosphere and form metallic oxides. The resulting bowls have a deep and lustrous sheen.
The now sadly destroyed city of Raqqa, located on the Euphrates River in Syria, was once home to the powerful caliph Harun al-Rashid (reigned 786–809), who was also featured in the popular A Thousand and One Nights. Stories about Syria’s fabled past, in part, inspired Western collectors to travel to the region. Charles Lang Freer (1954–1919) visited Syria in the early 1900s and amassed a noteworthy collection of ceramics that had been recently unearthed in Raqqa. In the first half of the thirteenth century, Syrian potters developed their own distinctive styles in response to luster-painted wares from Egypt and vibrant blue glazes from Iran. These wares, made both for local and regional markets, were used throughout Syria and beyond. In the 1260s, invading Mongols destroyed the city of Raqqa and put an end to this rich tradition. Fortunately, the ceramics were rediscovered in the late nineteenth century. Because these vessels had been buried for centuries, the glaze had become almost iridescent due to their exposure to moisture in the earth. Charles Lang Freer was particularly attracted to this surface quality of Raqqa ware.
Freer was also an early patron of the Pewabic Pottery, a ceramics workshop in Detroit founded by Mary Chase Perry Stratton (1867–1961) at the turn of the twentieth century, and he acquired thirty-five pieces between 1908 and 1918. An avid collector of ceramics, Freer was keenly interested in aesthetic similarities between pottery glazes and the rich surfaces of the paintings he acquired. For her part, Stratton was inspired by the iridescent glazes of the antique Near Eastern ceramics in Freer’s collection. In exchange for making his paintings available to Stratton for study, Freer challenged her to create a ruby red glaze. In 1909, she succeeded and went on to develop six iridescent hues for which Pewabic became famous.
“And lovely—delicately, subtly lovely—it is, this fragile bit of pottery whose surface catches the light and reflects it in opalescent, shimmering tints that defy naming.”
This red-violet bottle with its metallic shimmer is a fine example of the way Stratton experimented with glazing techniques by combining chemicals and colorants and by manipulating the atmosphere in the firing kiln. She applied a violet-green, copper-based iridescent glaze directly to the buff clay body of the bottle and fired it at an extremely high temperature, creating the opalescent surface that Freer admired and connected to his own collection of Syrian Raqqa ware. Though Stratton was responsible for the glaze recipes, she left her assistants to throw the vessels. This freed Stratton to devote herself entirely to the art of glazing, which she called “painting with fire.”
Freer’s abiding interest in iridescence informed how he displayed his collection. His choice to display his Raqqa ware directly across from the windows in the Peacock Room was likely a deliberate decision to showcase the ceramics’ shimmering glazes when the shutters were open to let in sunlight. You can see the Peacock Room illuminated in person every third Thursday of the month. You can also watch the opening of the shutters in the video below: