User:Laal Mariposa/Azurite (pigment)
Azurite is an inorganic pigment derived from the mineral of the same name.[1] 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.[1]: 23–26 In the Middle Ages and Renaissance, it was the most prevalent blue pigment in European paintings, appearing more commonly than the more expensive ultramarine.[1]: 26 Azurite's derivation from copper mines tends to give it a greenish hue, in contrast with the more violet tone of ultramarine.[2] 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.[2] 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.[1]: 26 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.[3]
History
Write about turning points in manufacturing or use of azurite.
Chemical Composition
Azurite is a basic compound that is coordinated with copper[4].
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[5]. Conservation studies of a 14th-15th century wall painting of San Antonio Abae in the church of San Pietro near Florence, Italy revealed that azurite degradation products are green. There is controversy of how best to restore azurite degradation becase the typical technique of applying ammonium carbonate and barium hydroxyide does produce a dark blue hue, but a scientific study completed in the late 1990's by Italian art conservationaists found that the dark blue hue is not azurite. Although it is clear that the degradation product of azurite is green, it was previously believed that the identity of this product is malachite. This study employed fourier transfrom infrared spectroscopy (FTIR) to discover that the main degradation product of azurite is not malachite, as previously believed, but rather is paratacamite. Paratacamite and atacamite are two different phases of a basic copper choloride and were previously found amonst azurite degradation products. These degradation products are distinghished using FTIR spectroscopy techniques.
The conversion of the green azurite degradation product to a dark blue compound is 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 Antionio Abate church wall painting changed color again. The blue color produced by the technique of using barium hydroxide and ammonium carbonate is copper hydroxide, and not azurite. Therefore, there is evidence to show that azurite conservation technqiues 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. (Van Asperen de Boer)
Association with Ultramarine
Azurite can often be used with ultramarine, perhaps to save costs because ultramarine was very expensive (Del Luigi). Due to its association with copper and malachite, a green pigment, the hue of azurite over time can change to a greenish blue hue. Thus, conservation studies may reveal where azurite and ultramarine, another popular blue pigment, were used. The stone used to produce ultramarine, lapis lazuli, has a more violet blue.
In Paintings
Azurite was used to paint the dark blue sky of a Rennaissance-era Spanish altarpiece painting by Bartolome Bermejo. In this work, the panel painting of St Jerome, is comprised of typical Spanish Rennaissance 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. Azurite was layered with other pigments in each section of the painting.
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References
- ^ a b c d Gettens, Rutherford J.; Fitzhugh, Elisabeth West (1993). "Azurite and Blue Verditer". In Roy, Ashok (ed.). Artists' Pigments: A Handbook of Their History and Characteristics. Vol. 2. Archetype. pp. 23–36.
- ^ a b Finlay, Victoria (2002). Color: A Natural History of the Palette. Random House. pp. 287–88.
- ^ Price, Michael (2000). "A Renaissance of Color: Particle Separation and Preparation of Azurite for Use in Oil Painting". Leonardo. 33 (4): 281–288. doi:10.1162/002409400552667. ISSN 0024-094X. JSTOR 1576902. S2CID 57571083.
- ^ Gettens, Rutherford; West Fitzhugh, Elisabeth (1993). "Azurite and Blue Verditer". Artists Pigments: A Handbook of Their History and Characteristics. London: Archetype Publications. pp. 23–33.
- ^ Dei, Luigi; Ahle, Andreas; Baglioni, Piero; Dani, Daniela; Ferroni, Enzo (1998). "Green Degradation Products of Azurite in Wall Paintings: Identification and Conservation Treatment". Studies in Conservation. 43 (2): 80–88.