Cobalt blue in the context of "Aluminium oxide"

Iznik pottery, or Iznik ware, named after the town of İznik in Anatolia where it was made, is a decorated ceramic that was produced from the last quarter of the 15th century until the end of the 17th century. The Ottoman Turkish motivation for creating İznik ware was to imitate the prestige and symbolic value of Chinese porcelain, not its specific decorative designs. While their conceptual origin lies in Chinese blue-and-white porcelain, their decorative design is a distinct Ottoman adaptation of the International Timurid style. This adaptation is marked by a transformation from the prototype's languid quality to a more forceful and contained design, distinguished by its intensity and three-dimensional feel. Technologically, these wares are unique, differing from the methods used for contemporary Iranian pottery and Ottoman architectural tilework. This distinct manufacturing process is thought to be an invention of Anatolian potters.

İznik was an established centre for the production of simple earthenware pottery with an underglaze decoration when, in the last quarter of the 15th century, craftsmen in the town began to manufacture high quality pottery with a fritware body painted with cobalt blue under a colourless transparent lead glaze. The change was almost certainly a result of active intervention and patronage by the recently established Ottoman court in Istanbul who greatly valued Chinese blue-and-white porcelain.

Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a 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, somewhat brittle, gray metal.

Cobalt-based blue pigments (cobalt blue) have been used since antiquity for jewelry and paints, and to impart a distinctive blue tint to glass. The color was long thought to be due to the 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 off poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), which was ultimately named for the kobold.

The flag of the U.S. state of Nevada was adopted in 1929, when governor Fred B. Balzar signed into law a bill adopting the new flag. Its design consists of a solid cobalt blue field with, in the upper hoist quarter, two crossed sprays of sagebrush (the state flower) forming a half-wreath. Centered within the wreath is an upward-pointing silver star (a reference to the state's nickname, the Silver State), with the state's name arched below it in evenly spaced golden-yellow letters. Above the wreath is a golden-yellow scroll touching its tips, bearing the words "Battle Born", one of the state's mottos (in reference to Nevada becoming a state during the American Civil War).

Blue is one of the three primary colours in the RGB (additive) colour model, as well as in the RYB colour model (traditional colour theory). It lies between violet and cyan on the spectrum of visible light. The term blue generally describes colours perceived by humans observing light with a dominant wavelength between approximately 450 and 495 nanometres. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called the Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective.

Blue has been an important colour in art and decoration since ancient times. The semi-precious stone lapis lazuli was used in ancient Egypt for jewellery and ornament and later, in the Renaissance, to make the pigment ultramarine, the most expensive of all pigments. In the eighth century Chinese artists used cobalt blue to colour fine blue and white porcelain. In the Middle Ages, European artists used it in the windows of cathedrals. Europeans wore clothing coloured with the vegetable dye woad until it was replaced by the finer indigo from America. In the 19th century, synthetic blue dyes and pigments gradually replaced organic dyes and mineral pigments. Dark blue became a common colour for military uniforms and later, in the late 20th century, for business suits. Because blue has commonly been associated with harmony, it was chosen as the colour of the flags of the United Nations and the European Union.

The stained glass windows of Chartres Cathedral are held to be one of the best-preserved and most complete set of medieval stained glass, notably celebrated for their colours, especially their cobalt blue. They cover 2600 square metres in total and consist of 167 windows illustrating biblical scenes, the lives of the saints and scenes from the life of trade guilds of the period.

Some windows survive from an earlier Chartres Cathedral, such as the three lancets on the west front (1145–1155, contemporary with those made for Abbot Suger at the Basilica of Saint-Denis) and the lancet south of the choir known as 'Notre-Dame de la Belle Verrière', famed for its Chartres blue (1180). However, most of the windows were probably made between 1205 and 1240 for the present church, taking in the Fourth Crusade (bringing a large number of important relics to Chartres) and the Albigensian Crusade, as well as the reigns of Philip II Augustus (1180–1223) and Louis VIII (1223–1226), with the building's consecration finally occurring in 1260 under Louis IX (1226–1270).

The Frida Kahlo Museum (Spanish: Museo Frida Kahlo), also known as the The Blue House (La Casa Azul) for the structure's cobalt-blue walls, is a historic house museum and art museum dedicated to the life and work of Mexican artist Frida Kahlo. It is in the Colonia del Carmen neighborhood of Coyoacán in Mexico City. The building was Kahlo's birthplace, the home where she grew up, lived with her husband Diego Rivera for a number of years, and where she later died in a room on the upper floor. In 1957, Rivera donated the home and its contents to turn it into a museum in Kahlo's honor.

The museum contains a collection of artwork by Kahlo, Rivera, and other artists, along with the couple's Mexican folk art, pre-Hispanic artifacts, photographs, memorabilia, and personal items. The collection is displayed in the rooms of the house that remains much as it was in the 1950s.