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Environment Science

Ancient Egyptian Blue Pigment Boosts Energy Efficiency

Thousands of years ago, in ancient Egypt, a very special shade of blue was created. The Egyptians had used it in their depictions of God’s and royalty because of its radiance and beauty. Scientists today have found another use for it. This ancient blue’s new purpose now is to boost energy efficiency and generate clean renewable power.

Cuprorivaite, also known as Egyptian Blue, is a man-made pigment made up of calcium, strontium, and barium copper silicate. When it absorbs visible light, it then emits light in the near-infrared range. A study was conducted by a team of researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) where they measured the temperature of surfaces coated in Egyptian Blue (and related compounds) while they were exposed to sunlight. They discovered that the fluorescent blues can emit nearly 100 percent as many photons as they absorb. The energy efficiency of the emission process is up to 70 percent (the infrared photons carry less energy than visible photons).

This unique quality makes Egyptian Blue an ideal candidate for the use in energy efficiency boosting color choices on buildings. Roofs and walls painted with this color will be cooler and therefore save on electricity consumption (and cost) by reducing the energy use for air conditioning. Due to these qualities, the pigment can enable solar generation of electricity via windows. If the window is tinted with this blue, photovoltaic cells on the edges can convert the fluoresced near-infrared energy to electricity.

Temperature rise in sunlight
“Berkeley Lab scientists measured the temperature rise above air temperature observed in full sun for five pigment-coated samples, each 75 millimeters square. The white and black samples show low and high temperatures.” (Credit: Berkeley Lab)

These findings contribute to the current knowledge about which colors are most effective for cooling rooftops and facades in sunny climates. White is still the most effective and conventional color choice for keeping a building cool by reflecting sunlight but it is not the ideal choice aesthetically as it can get dirty easily and is difficult to maintain. Because of that, there is a constant lookout for other viable color options. Previously, Berkeley Lab researchers found that fluorescent ruby-red pigments can be an effective alternative to white. Further, they found that fluorescent green and black colors can be produced with yellow and orange co-pigments (the new findings were recently published in the Journal of Applied Physics); and now this insight on Egyptian blue adds to the menu of cooling color choices.

This work was led by Paul Berdahl of the Heat Island Group as part of the Cool Walls project supported by the Electric Program Investment Charge program of the California Energy Commission. Their research has led to information that benefits our planet and the people’s pocket. Because of it, we know that reflective roofs and walls can cool buildings and cars and color is an important factor of this. On the human-scale, using color to reflect light reduces the need for air conditioning (benefiting our pockets) and mitigates the urban heat island effect (benefiting our environment). On a global scale, by reflecting the sun’s rays back to space, these cool materials also release less heat into the atmosphere, thus cooling the planet and offsetting the warming effects of substantial amounts of greenhouse gas emissions (benefiting our planet).

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