Ultramarine is a deep blue pigment historically derived from lazurite, the principal component of the metamorphic rock lapis lazuli. The pigment was produced by grinding the stone and undergoing a complex washing process to isolate the blue mineral, which made it exceptionally valuable. The name ultramarine comes from the Latin ultramarinus, meaning “beyond the sea,” referring to its import into Europe by Italian traders from mines in Afghanistan during the 14th and 15th centuries. Venice served as a major center for this trade and distribution. Ultramarine was among the finest and most expensive blue pigments used by Renaissance painters, at times valued as highly as gold in Europe. It was especially used for the robes of the Virgin Mary, symbolizing purity, holiness, and status. The pigment remained costly until the development of synthetic ultramarine in 1826. Ultramarine is generally considered a permanent pigment under stable conditions, though it may discolor or fade under unfavorable environmental factors.
Structure The pigment consists primarily of a zeolite-based mineral containing small amounts of polysulfides. It occurs in nature as a proximate component of lapis lazuli containing a blue cubic mineral called lazurite. In the Colour Index International, the pigment of ultramarine is identified as P. Blue 29 77007. The major component of lazurite is a complex sulfur-containing sodium-silicate (Na8–10Al6Si6O24S2–4), which makes ultramarine the most complex of all mineral pigments. Some chloride is often present in the crystal lattice as well. The blue color of the pigment is due to the S−3 radical anion, which contains an unpaired electron.
Visual properties
The best samples of ultramarine are a uniform deep blue while other specimens are of paler color. Particle size distribution has been found to vary among samples of ultramarine from various workshops. Numerous grinding techniques used by painters have resulted in different pigment/medium ratios and particle size distributions. The grinding and purification process results in pigment with particles of various geometries. Different grades of pigment may have been used for different areas in a painting, a characteristic that is sometimes used in art authentication.
Shades and variations
International Klein Blue (IKB) a deep blue hue first mixed by the French artist Yves Klein.
Electric Electric ultramarine is the tone of ultramarine that is halfway between blue and violet on the RGB (HSV) color wheel, the expression of the HSV color space of the RGB color model.
Production
Natural production Lapis lazuli stone was historically mined near Sar-i-Sang in modern-day Afghanistan and traded to Mesopotamia and ancient Egypt as early as the third millennium BCE. Ultramarine was unknown until the early 13th century, though lapis lazuli had been used as a pigment from the 5th century on (for instance in Buddhist cave temples) by the simple expedient of grinding down the best available grade of the mineral, showing as few inclusions as possible. The resulting blue pigment remained more or less ashy. The method to extract true ultramarine was first described by Aḥmad ibn Yūsuf al-Tifāshī (d. 1254) in his lapidary Kitāb azhār al-afkār fī jawāhir aḥjār (The Blossoms of Thoughts Regarding Precious Stones"). Two centuries later, it became known in Europe through Cennino Cennini's treatise (15th century). This process consisted of grinding the lapis lazuli mineral, mixing the ground material with melted wax, resins, and oils, wrapping the resulting mass in a cloth, and then kneading it in a dilute lye solution, a potassium carbonate solution prepared by combining wood ash with water. The blue lazurite particles collect at the bottom of the pot, while the colorless crystalline material and other impurities remain at the top. This process was performed at least three times, with each successive extraction generating a lower quality material. The final extraction, consisting largely of colorless material as well as a few blue particles, brings forth ultramarine ash which is prized as a glaze for its pale blue transparency. This extensive process was specific to ultramarine because the mineral from which it is derived has a combination of both blue and colorless pigments. If an artist were to simply grind and wash lapis lazuli, the resulting powder would be a greyish-blue color that lacks purity and depth of color since lapis lazuli contains a high proportion of colorless material. Although the lapis lazuli stone itself is only moderately expensive, the lengthy process of pulverizing, sifting, and washing to produce ultramarine makes the natural pigment quite valuable and roughly ten times more expensive than the stone it comes from. The high cost of the imported raw material and the long laborious process of extraction combined has been said to make high-quality ultramarine as expensive as gold.
Synthetic production In 1990, an estimated 20,000 tons of ultramarine were produced industrially. The raw materials used in the manufacture of synthetic ultramarine are the following:
white kaolin, anhydrous sodium sulfate (Na2SO4), anhydrous sodium carbonate (Na2CO3), powdered sulfur, powdered charcoal or relatively ash-free coal, or colophony in lumps. The preparation is typically made in steps:
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