User:Laal Mariposa/Azurite (pigment)

A photo of the azurite mineral, as found in nature.

Azurite is an inorganic pigment derived from the mineral of the same name. It was likely used by artists as early as the Fourth Dynasty in Egypt, but it was less frequently employed than synthetically produced copper pigments such as Egyptian Blue. In the Middle Ages and Renaissance, it was the most prevalent blue pigment in European paintings, appearing more commonly than the more expensive ultramarine. Azurite's derivation from copper mines tends to give it a greenish hue, in contrast with the more violet tone of ultramarine. Azurite is also less stable than ultramarine, and notable paintings such as Michelangelo's The Entombment have seen their azure blues turn to olive green in time. Azurite pigment typically includes traces of malachite and cuprite; both minerals are found alongside azurite in nature, and they may account for some of the green discoloration of the pigment. The particle size of azurite pigment has been shown to have a significant effect on its chromatic intensity, and the manner of grinding and preparing the pigment therefore has a major impact on its appearance.

History

Azurite is naturally occurring mineral found particularly in copper-mining areas of the world. It is often found with malachite, a green basic carbonate of copper. There is evidence that azurite has been used since the dawn of modern civilization, dating all the way back to the Fourth Dynasty in Egypt. At certain points of history, azurite was even more popular than ultramarine despite ultramarine receiving more attention. During the Middle Ages and Renaissance, the two were closely related as azurite wold often be used as an under-paint for ultramarine, possibly to lower costs as ultramarine was the more expensive pigment of the two.

Hungary was the main supplier of European azurite until the mid 17th century, until it was invaded by the Ottoman empire, but now Hungary is again the most popular source of the pigment. Azurite was popular in the Far East, though limited in Pre-Columbian indigenous and later Spanish Mission Church paintings.

With the invention of Prussian blue in 1704, azurite was displaced as the go-to blue pigment in certain European paintings, but it still remained largely popular, possibly because of azurite's simple preparation. Another synthetic blue pigment that was used similarly as azurite is blue verditer, a basic carbonate of copper and commonly used to paint houses in the 17th century.

A photo of the azurite pigment after it has been ground.

Chemical Composition

Azurite is a basic compound that is coordinated with copper. Azurite was popular due to its stability in various light and atmosphere conditions, making it easier to store. Although azurite is permanent in oil and tempura paint, it is darkened when exposed to sulfur and this can be seen in mural paintings that use azurite. Azurite turns greens due to its degradation to malachite and other products.

Azurite is relatively easy to identify in conservation studies because of its characteristic ability to produce copper-coordinated compounds, ability to dissolve in acidic solution, and birefringence interactions with light. Various spectroscopy methods such as X-ray diffraction, emission spectroscopy, IR spectroscopy, and Raman spectrophotometry.

Conservation

Due to its association with copper and malachite, a green pigment, the hue of azurite over time can change to a greenish blue hue. Conservation studies of a 14th-15th century wall painting of San Antonio Abate in the church of San Pietro near Florence, Italy revealed that the azurite degradation product, once though to be malachite, is actually paratacamite. Paratacamite and atacamite are two different phases of a basic copper chloride that are both found amongst azurite degradation products and can be distinguished using FTIR techniques.

There is controversy of how best to restore azurite degradation because the typical technique of applying ammonium carbonate and barium hydroxide does produce a dark blue hue, but this study, completed in the late 1990's by Italian art conservationists, found that the dark blue hue is not azurite. Rather, the dark blue compound is produced due to the action of barium hydroxide, and not ammonium carbonate, although both are present in the typical conservation technique used to restore azurite. The blue color is not stable, moreover, as two years after the restoration of the San Antonio Abate church wall painting changed color again. Therefore, there is evidence to show that azurite conservation techniques must be updated and continued to be scientifically studied so that not to damage the paintings that are being restored containing this pigment.

Grinding

A finer grind makes azurite appear more pale whereas a coarser grind makes it more pigmented. For use in early modern-era paintings, azurite was ground by hand. Artists employed special techniques which required training to grind the pigment in order to achieve different intensities. Azurite grinding craftsmanship therefore varies across workshops. Different grinding styles are characterized by both the pigment-medium ratio and the particle size distribution of the pigment. Azurite particles are irregular in size and often contains impurities such as malachite and cuprite due to its close association with these compounds. The pigment to volume concentration of azurite is difficult to study because azurite was often mixed with varying amounts of lead white, especially in early Netherlandish paintings.

Association with Ultramarine

Azurite can often be used with ultramarine, perhaps to save costs because ultramarine was very expensive . The two can be distinguished by contrasting the blue-green degradation of azurite with the blue-violet degradation of ultramarine as they are sourced from two different minerals. Whereas ultramarine was ground a bit finer than azurite, azurite is a strong pigment if left coarsely ground, so artists took care not to grind it too fine.

The Mystic Lamb, a painting in which azurite is used.

In the painting Mystic Lamb, ultramarine and azurite were used in nearly the same areas and in similar particle size distributions. Both pigments are finely ground. However, The Mystic Lamb alone should not be used to generalize the style of azurite use in early Netherlandish paintings. In a different early Netherlandish painting from the group D. Bouts, azurite and ultramarine are used together, but they are ground much coarser.

In Paintings

Azurite was used to paint the dark blue sky of a Renaissance-era Spanish altarpiece painting by Bartolome Bermejo. In this work, the panel painting of St Jerome, is comprised of typical Spanish Renaissance painting techniques and materials, of which azurite was common. During this time, azurite was a common pigment used to paint a blue sky. In this painting, azurite is also combined with lead white to paint the green robe of the Saint.

Christ Taking Leave of Mother (circa 1520).

In the 1520 painting titled Christ Taking Leave of His Mother by Altdorfer, the color blue is supplied by azurite used to paint the garments of figures depicted. In addition, azurite is mixed with lead white to paint the sky.

Azurite has been used to produce greens for foliage and landscapes and mixed with red pigments to produce violet.