Egyptian Blue

The Chemistry of Egyptian Blue

Cu2(CO3)(OH2) + 8 SiO2 + 2 CaCO3 −› 2 CaCuSi4O10 + 3 CO2 + H2O

malachıte sanD lıme egyPtıan blue

The chemical formula for Egyptian blue is CaCuSi4O10. The synthesis of Egyptian blue is shown above by this chemical equation at a temperature between 800℃ and 900℃. A fl ux made from a mixture of sodium sulfate, soda (Na2Co3), and sodium chloride was used to help the synthesis.

Fig.1 The pigment Egyptian blue in its powdered state. Image: cc by fk 1954 To understand the blue color, we must fi rst understand that the electrons in an atom exist in orbitals. Each orbital can hold up to two electrons, and depending on the identity of the atom and its local environment, they can have various energies.

Fig.2 The chemical structure of Egyptian blue. Image: Nick Greeves, cc by-nc-sa 2.0

The blue color of Egyptian blue can be explained by crystal fi eld theory. A qualitative example of the copper d-orbital splitting in Egyptian blue can be seen in Fig.3. Here, the spatial arrangement of the oxygen atoms around copper causes an energy difference in the metal orbitals. When photons of the appropriate energy are absorbed, electrons can move from one level to another; the wavelengths that refl ect back to our eye are the color we perceive. Because electrons are traversing from one metal d-orbital to another, these are known as d-d transitions. The energy difference and the precise ordering of these levels depend on many factors including the nature of the metal and the surrounding environment. Even slight differences in makeup can lead to drastically different colors, as seen in another pigment of interest: verdigris.

Fig.3 A qualitative crystal fi eld diagram of copper in Egyptian blue. Image: Courtesy of Christopher B. Durr

Egyptian Blue

in Art

As a symbol of health, happiness, and fortune, blue assumed an important place in the decoration of devotional and ceremonial objects in ancient Egyptian society. Egyptians extracted blue pigments from minerals such as azurite and lapis lazuli. Egyptians are also credited with the invention of this synthetic color pigment, so-called Egyptian blue.

In accordance with ancient Egyptian beliefs about the afterlife, the interior sides of this wooden coffin (pp.9&10) in the Mead’s collection are decorated with hieroglyphs, figures, and other iconography that symbolize the soul’s journey within the realm of the dead. Several bands of human-like figures represent Egyptian deities who guide the dead. The three most clearly visible rows on the inside consist of a combination of human and animalheaded figures. At the very top of the coffin’s bottom sits a pharaoh, with a bird’s wing stretched above his head. The bright colors that the artisans used to paint the case are mainly red, blue, green, and occasionally white. Blue is the most prominent, decorating the bodies and headdresses of the various figures on the interior and exterior walls, as well as the thick lines that separate the different sections of the coffin’s sides. The predominant blue coloring illustrates the significance of this pigment in ancient Egypt.

references

“Ancient Egyptian Coffins and Sarcophagi.” Google Arts & Culture. Google, n.d. https://artsandculture.google.com/ usergallery/ancient-egyptian-coffinsand-sarcophagi/sgIingkkfusllg.

“Egyptian Art.” Essential Humanities, July 2010. http://www.essential-humanities.net/ world-art/egyptian/.

Unknown (Egyptian). Coffin, ca.1077–943 bce. Painting, plaster, and wood. Gift of Dr.StephenH.Weeks. p.1905.2 & p.1905.1. Photos: Mead Art Museum

Details of p.1905.1. Photos: Mead Art Museum