Extraction

Lapis lazuli is a semiprecious stone prized since antiquity for its intense blue color. It has been mined in the Badakhshan province of Afghanistan for 6,500 years, and trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian sites. Lapis beads have been found at neolithic burials in Mehrgarh in Pakistan, the Caucasus, and as far from Afghanistan as Mauritania in northwest Africa.

Many of the blues in painting from medieval Illuminated manuscripts to Renaissance panels were derived from lapis lazuli and used in tempera paint. Ground to a powder and processed to remove impurities and isolate the component lazurite, it forms the pigment ultramarine. This clear bright blue, which was one of the few available to painters before the 19th century, was rare and expensive.

As tempera painting was superseded by the advent of oil paint in the Renaissance, painters found that the brilliance of ultramarine was greatly diminished when it was ground in oil and this, along with its cost, led to a steady decline in usage. Since the synthetic version of ultramarine was discovered in the 19th century, along with other 19th century blues such as cobalt blue, production and use of the natural variety has almost ceased, though several pigment companies still produce it and some painters are still attracted to its brilliance and its romantic history.

The first noted use of lapis lazuli as a pigment can be seen in the 6th- and 7th-century AD cave paintings in Afghanistan temples, near the most famous source of the mineral. Lapis lazuli has also 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 c.1100. Natural ultramarine is the most 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. At the beginning of the 13th century an improved method came into use, described by the 15th century artist Cennino Cennini.

This process consisted of 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. The blue particles collect at the bottom of the pot, while the impurities and colorless crystals remain in the mass. 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.

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, which destroy the blue color producing hydrogen sulfide in the process. Acetic acid attacks the pigment at a much slower rate than mineral acids. Because of this susceptibility, ultramarine was only used for frescoes when it was applied is such a way that the pigment was mixed with a binding medium and applied over dry plaster.

European artists used the pigment sparingly, reserving their highest quality blues for the robes of Mary and the Christ child. As a result of the high price, artists sometimes economized by using a cheaper blue, azurite, for underpainting. Most likely imported to Europe through Venice, the lazuli pigment was seldom seen in German art or art from countries north of Italy. Due to a shortage of azurite in the late 16th and 17th century the demand for the already expensive pigment increased dramatically.

In 1814 Tassaert observed the spontaneous formation of a blue compound, very similar to lazuli if not identical with it, in a lime kiln at St. Gobain, which caused the French Society for the Encouragement of Industry to offer, in 1824, a prize for the artificial production of the precious color. Processes were devised by Jean Baptiste Guimet and by Christian Gmelin, then professor of chemistry in Tubingen. While Guimet kept his process a secret Gmelin published his, and thus became the originator of the artificial ultramarine industry.

It was once believed that lapis had medicinal properties. It was ground down, mixed with milk and applied as a dressing for boils and ulcers. The Romans believed that lapis was a powerful aphrodisiac. In the Middle Ages, it was thought to keep the limbs healthy, and free the soul from error, envy and fear.

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