Ultramarine is a deep blue color pigment which was originally made by grinding lapis lazuli into a powder.

[5][6] Much of the expansion of ultramarine can be attributed to Venice which historically was the port of entry for lapis lazuli in Europe.

It occurs in nature as a proximate component of lapis lazuli containing a blue cubic mineral called lazurite.

[16][dubious – discuss] 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.

[17] A method to produce ultramarine from lapis lazuli was introduced by the 5th century for use in Buddhist cave temples.

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.

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.

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.

Even a small addition of zinc oxide to the reddish varieties especially causes a considerable diminution in the intensity of the color.

[21] Modern, synthetic ultramarine blue is a non-toxic, soft pigment that does not need much mulling to disperse into a paint formulation.

[4] 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.

[31] 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.

Dilute HCl, HNO3, and H2SO4 rapidly destroy the blue color, producing hydrogen sulfide (H2S) in the process.

The pigment was mixed with a binding medium like egg to form a tempera and applied over dry plaster, such as in Giotto di Bondone's frescos in the Cappella degli Scrovegni or the Arena Chapel in Padua.

European artists used the pigment sparingly, reserving their highest quality blues for the robes of Mary and the Christ child, possibly in an effort to show piety, spending as a means of expressing devotion.

Due to a shortage of azurite in the late 16th and 17th century, the price for the already-expensive ultramarine increased dramatically.

[37][38] In 1814, Tassaert observed the spontaneous formation of a blue compound, very similar to ultramarine, if not identical with it, in a lime kiln at St.

[39] In 1824, this caused the Societé pour l'Encouragement d'Industrie to offer a prize for the artificial production of the precious color.

[40][21] Easel paintings and illuminated manuscripts have revealed natural ultramarine in a perfect state of preservation even though the art may be several centuries old.

The cause of this has been debated among experts, however, potential causes include atmospheric sulfur dioxide and moisture, acidity of an oil- or oleo-resinous paint medium, or slow drying of the oil during which time water may have been absorbed, creating swelling, opacity of the medium, and therefore whitening of the paint film.

These observations have led experts to speculate if the natural pigment's fading may be the result of contact with the lime plaster of fresco paintings.

[21] During World War I, the RAF painted the outer roundels with a color made from ultramarine blue.