Ultramarine is a deep blue pigment historically derived from lazurite, the principal component of the metamorphic rock lapis lazuli.Webster's New World Dictionary of American English, Third College Edition, 1988. 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 , 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 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
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.Maerz and Paul A Dictionary of Color New York:1930--McGraw Hill Color Sample of Ultramarine: Page 105, Plate 41, Color Sample F12. Ultramarine is shown as being one of the colors on the bottom of the plate representing the most highly saturated colors between blue and violet (the colors on the right of the plate represent the most highly saturated colors between violet and rose); ultramarine is shown as being situated at a position exactly one-half of the way between blue and violet. A nearly identical color is color wheel indigo.
International Klein Blue International Klein Blue (IKB), a deep blue hue first mixed by the French artist Yves Klein.
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.Lara Broecke, Cennino Cennini's Il Libro dell'Arte: a New English Translation and Commentary with Italian Transcription, Archetype 2015, pp. 89–90. 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: The first part of the process takes place at 700 to 750 °C in a closed furnace, so that sulfur, carbon and organic substances give reducing conditions. This yields a yellow-green product sometimes used as a pigment. In the second step, air or sulfur dioxide at 350 to 450 °C is used to oxidize sulfide in the intermediate product to S2 and Sn chromophore molecules, resulting in the blue (or purple, pink or red) pigment. The mixture is heated in a kiln, sometimes in brick-sized amounts. The resultant solids are then ground and washed, as is the case in any other insoluble pigment's manufacturing process; the chemical reaction produces large amounts of sulfur dioxide. (Flue-gas desulfurization is thus essential to its manufacture where SO2 pollution is regulated.)
Ultramarine poor in silica is obtained by fusing a mixture of soft clay, sodium sulfate, charcoal, sodium carbonate, and sulfur. The product is at first white, but soon turns green "green ultramarine" when it is mixed with sulfur and heated. The sulfur burns, and a fine blue pigment is obtained. Ultramarine rich in silica is generally obtained by heating a mixture of pure clay, very fine white sand, sulfur, and charcoal in a muffle furnace. A blue product is obtained at once, but a red tinge often results. The different ultramarines—green, blue, red, and violet—are finely ground and washed with water.
Synthetic ultramarine is a more vivid blue than natural ultramarine, since the particles in synthetic ultramarine are smaller and more uniform than the particles in natural ultramarine and therefore diffuse light more evenly. Its color is unaffected by light nor by contact with oil or lime as used in painting. Hydrochloric acid immediately bleaches it with liberation of hydrogen sulfide. Even a small addition of zinc oxide to the reddish varieties especially causes a considerable diminution in the intensity of the color. Modern, synthetic ultramarine blue is a non-toxic, soft pigment that does not need much mulling to disperse into a paint formulation.
History Antiquity and Middle Ages The name derives from Middle Latin , literally "beyond the sea" because it was imported from Asia by sea. In the past, it has also been known as azzurrum ultramarine, , , , . The current terminology for ultramarine includes natural ultramarine (English), (French), (German), (Italian), and (Spanish). The first recorded use of ultramarine as a color name in English was in 1598.Maerz and Paul A Dictionary of Color New York:1930--McGraw Hill Page 206
Ancient Egyptians used lapis lazuli in solid form for ornamental applications in jewelry, however, there is no record of them successfully formulating lapis lazuli into paint. Archaeological evidence and early literature reveal that lapis lazuli was used as a semi-precious stone and decorative building stone from early Egyptian times. The mineral is described by the classical authors Theophrastus and Pliny. There is no evidence that lapis lazuli was used ground as a painting pigment by ancient Greeks and Romans. Like ancient Egyptians, they had access to a satisfactory blue colorant in the synthetic copper silicate pigment, Egyptian blue.
The first noted use of lapis lazuli as a pigment can be seen in 6th and 7th-century paintings in Zoroastrian and Buddhist cave temples in Afghanistan, near the most famous source of the mineral. Lapis lazuli has been identified in Chinese paintings from the 10th and 11th centuries, in Indian mural paintings from the 11th, 12th, and 17th centuries, and on Anglo-Saxon and Norman illuminated manuscripts from . Ultramarine also appears in Islamic illuminated manuscripts from the 15th and 16th centuries throughout modern-day Afghanistan and Iran.
Renaissance
Venice was central to both the manufacturing and distribution of ultramarine during the early modern period. The pigment was imported by Italian traders during the 14th and 15th centuries from mines in Afghanistan. Other European countries employed the pigment less extensively than in Italy; the pigment was not used even by wealthy painters in Spain at that time.
During the Renaissance, ultramarine was the finest and most expensive blue that could be used by painters. Color infrared photogenic studies of ultramarine in 13th and 14th-century Sienese panel paintings have revealed that historically, ultramarine has been diluted with white lead pigment in an effort to use the color more sparingly given its high price. The 15th century artist Cennino Cennini wrote in his painters' handbook: "Ultramarine blue is a glorious, lovely and absolutely perfect pigment beyond all the pigments. It would not be possible to say anything about or do anything to it which would not make it more so."Lara Broecke, Cennino Cennini's Il Libro dell'Arte, a New English Translation and Commentary with Italian Transcription, Archetype 2015, p. 89. Natural ultramarine is a difficult pigment to grind by hand, and for all except the highest quality of mineral, sheer grinding and washing produces only a pale grayish blue powder.
The pigment was most extensively used during the 14th through 15th centuries, as its brilliance complemented the vermilion and gold of illuminated manuscripts and Italian panel paintings. It was valued chiefly on account of its brilliancy of tone and its inertness in opposition to sunlight, oil, and slaked lime. It is, however, extremely susceptible to even minute and dilute mineral acids and acid vapors. Dilute HCl, HNO3, and H2SO4 rapidly destroy the blue color, producing hydrogen sulfide (H2S) in the process. Acetic acid attacks the pigment at a much slower rate than mineral acids.