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Ultramarine

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Ultramarine is a deep, brilliant blue pigment used by artists throughout history.

Natural ultramarine painted
Natural ultramarine painted

It is prized for its intense color and its ability to remain stable under light. Historically, the pigment was made by processing a semi-precious stone called lapis lazuli. This mineral is a complex sodium-silicate containing sulfur, known as lazurite. The blue color comes from a radical anion, which is a particle with an unpaired electron. Because of its beauty and rarity, ultramarine has held immense cultural and economic value for centuries.

Creating natural ultramarine is a complex, multi-step chemical extraction. Simply grinding lapis lazuli does not work for high-quality painting. Doing so only produces an ashy, greyish-blue powder because the stone contains many colorless impurities. To extract the true blue, the ground mineral is mixed with melted wax, resins, and oils. This mixture is wrapped in cloth and kneaded in a dilute lye solution. Lye is a potassium carbonate solution made from wood ash and water. During this kneading, the blue lazurite particles settle at the bottom of the container. The colorless materials stay at the top. This process is repeated at least three times. Each successive extraction produces a lower quality of pigment. The final, weakest extraction is called ultramarine ash, which is used as a pale, transparent glaze.

Ultramarine comes in various grades based on its purity and particle size. The best samples are a uniform, deep blue, while other specimens appear much paler. Different artists used various grinding techniques to change the particle size distribution. This resulted in different ratios of pigment to the medium used in the paint. Some painters used different grades for different parts of a single painting. This variation is sometimes used by experts today for art authentication. There are also specific color variations like International Klein Blue (IKB), which was mixed by the artist Yves Klein. Another variation is electric ultramarine, which sits halfway between blue and violet on the RGB color wheel.

The history of ultramarine is a story of long-distance trade and immense cost. The name comes from the Latin *ultramarinus*, meaning "beyond the sea." This refers to how Italian traders imported the pigment from Afghanistan during the 14th and 15th centuries. Venice served as the primary European port for the entry of lapis lazuli. Because the extraction process was so laborious, the pigment became incredibly expensive. In Europe, its price between the 14th and 15th centuries was comparable to the price of gold. It was roughly ten times more expensive than the raw stone itself.

During the Renaissance, ultramarine was the most prestigious blue available to painters. It was frequently used to paint the robes of the Virgin Mary. In this context, the color symbolized both holiness and humility. Because it was so costly, artists sometimes used it sparingly. Infrared studies of 13th and 14th-century Sienese paintings show that artists diluted ultramarine with white lead. This allowed them to cover larger areas while still using the precious blue. It was also used in illuminated manuscripts and Islamic manuscripts across Afghanistan and Iran. In many traditions, its brilliance complemented other expensive colors like gold and vermilion.

In 1826, a major change occurred with the invention of synthetic ultramarine. This modern version is produced industrially using specific raw materials. These include white kaolin, sodium sulfate, sodium carbonate, powdered sulfur, and charcoal. The production involves heating these materials in a closed furnace at 700 to 750 °C. This initial step creates a yellow-green product. In the second step, air or sulfur dioxide is used at 350 to 450 °C to oxidize the sulfide. This chemical reaction transforms the material into a blue, purple, pink, or red pigment. By 1990, an estimated 20,000 tons of synthetic ultramarine were being produced each year.

Synthetic ultramarine has different properties than the natural version. It is often more vivid because its particles are smaller and more uniform. This uniformity allows the pigment to diffuse light more evenly. While it is stable against light and oil, it is not invincible. For example, hydrochloric acid will immediately bleach the color. This happens because the acid liberates hydrogen sulfide. However, modern synthetic ultramarine is non-toxic and easy for artists to use. It remains a fundamental tool in the world of color and art science.

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