From Past to Present: Egyptian Blue

From Ancient Times to Today: Egyptian Blue The colour blue, which due to its connections with the sky and the Nile was thought to symbolize the cosmos, creation and fertility, was of great importance to ancient Egyptian civilization. However, in antiquity, only earth colours—pigments present in the upper layers of soil—were available as pigments, which made it difficult for Egyptian painters to obtain blue. Based on research conducted, it is believed that Egyptian blue was first used around 2600 BCE. From this date onwards, the use of this pigment expanded steadily throughout the ancient world and spread towards Mesopotamia and the Roman Empire until it disappeared in the Dark Ages. An Egyptian formula for the pigment is unfortunately not known, but Vitruvius, a Roman writer who lived in the 1st century BCE, reported that the pigment's content consisted of sand, copper (from a mineral such as azurite or malachite) and natron, a naturally occurring mixture of sodium compounds (including sodium carbonate). Egyptian blue (chemical formula: CaCuSi4O10) was obtained by heating these materials to 800–900°C and adding lime, a calcium-containing substance probably found as an impurity in sand. Whether produced intentionally or by accident, the production of Egyptian blue was a remarkably impressive achievement. Maintaining the temperature control necessary for a successful reaction, as well as achieving precise oxygen addition, must have been extremely difficult. The stability of the pigment over time is another example of the competence of Egyptian chemists. For instance, the composition found in artworks from the Old Kingdom (approximately 2600–2100 BCE), such as the mastaba (or tombs) of Mereruka, is nearly identical to that found in a mummy coffin from the Greco-Roman period (approximately 330 BCE–400 CE). In addition to its successful use in the past, Egyptian blue pigment appears set to continue its impact today. As an exciting development for chemists and artists, it was reported in 2009 that Egyptian blue displays extraordinary brightness in the near-infrared region. This property means that the pigment can be easily detected in a completely non-destructive manner by illuminating ancient artworks with near-infrared radiation. The luminescence is so powerful that the presence of even minute amounts of Egyptian blue can be detected even when no blue colour is visible to the naked eye. The British Museum successfully used this technique by detecting pigment on several sculptures from the Parthenon, providing the first evidence that the Elgin Marbles were once painted. In addition to art historians using the fluorescence property, chemists today are also recognizing that this material may have significant applications. For example, the long luminescence lifetime of near-infrared and its greater penetration depth in human tissue compared to UV or visible photons increases the possibility of obtaining more detailed and high-resolution biomedical images by using the pigment as an imaging agent. Furthermore, Egyptian blue is a cost-effective substitute for expensive lanthanide compounds typically used in security inks. Researchers at the Lawrence Berkeley National Laboratory in California found a special shade of blue to increase the energy efficiency of buildings by keeping walls and roofs cool in hot regions and to increase the production of certain types of solar cells through high near-infrared emissions. Although it was already known that photons absorbed by the material could be emitted in the near-infrared range, new research shows that the effect could be 10 times more powerful than previously thought, with the material being able to emit nearly as many photons as it absorbs. Berkeley Lab researchers who measured the temperatures of surfaces coated with Egyptian blue and related compounds when exposed to sunlight found that fluorescent blues were able to emit nearly 100 per cent of the photons they absorbed. The energy efficiency of the emission process reaches up to 70 per cent (near-infrared photons carry less energy than visible photons). This discovery expands our understanding of colours that work well for cooling roofs and facades in hot regions. Although white is the most conventional and efficient option for keeping a building cool by reflecting sunlight and reducing energy use for air conditioning, building owners often prefer non-white colours for aesthetic reasons. Understanding Egyptian blue expands the palette of cooling colour options. In theory, this could result in integrated PV applications such as blue-tinted solar windows and transparent cells designed to absorb the near-infrared region of the light spectrum. In addition to the cooling potential for buildings, the fluorescence of Egyptian blue may also be useful in solar energy production. Photovoltaic cells at the edges of windows tinted with blue can convert fluorescent near-infrared energy into electricity. Sources https://www.ancient-origins.net/ancient-technology/egyptian-blue-oldest-artificial-pigment-ever-produced-001745 https://www.webexhibits.org/pigments/indiv/overview/egyptblue.html https://www.chemistryworld.com/features/egyptian-blue-more-than-just-a-colour/9001.article https://heatisland.lbl.gov/news/article/egyptian-blue-energy-efficiency https://www.indiatoday.in/education-today/gk-current-affairs/story/egyptian-blue-artificial-pigment-solarenergy- 1366508-2018-10-11 https://pv-magazine-usa.com/2018/10/11/scientists-give-solar-pv-a-paint-job/ Compiled by - B. Serhat Cengiz