Egyptian blue was one of the famous pigments of the ancient world. Not only was it a scientific achievement, it has become an important historical signifier because it only came from contact with Egypt. It's now being used in advanced technology that see right through your skin.
What do you get when you toss calcium carbonate, copper-containing metal, and a lot of sand in a very hot fire? Probably nothing. That's why it was so impressive that Egyptians were able to turn those ingredients into something thousands of years ago. The three ingredients together can form calcium copper silicate, or Egyptian blue pigment -but the process is arduous and exact. First of all, a flux is needed. A flux is an ingredient added to a firing process that lowers the melting point of the other ingredients. Potash or calcium carbonate are common fluxes. Even with the flux, the fire used to melt the substances has to get up to about 950 degrees celsius. That's tough to make today, let alone 4,500 years ago.
Once the Egyptians started making the compound, it was enormously popular. Egyptian blue was a vivid pigment that resisted fading. It started appearing along trade-routes, spreading to other civilizations. These days, it's used to determine whether an ancient civilization was in contact with Egypt, giving us an economic and political picture of the ancient world. It colored the classical world for over five thousand years, and didn't lose popularity until the end of the first millennium AD.
Egyptian blue, after a long spell of obscurity, may become very popular again. It has a special property. Hit it with visible red light, and it will give off infrared. It will give off infrared for a prolonged period of time. This is helpful if you're an archaeologist and you want to determine what kind of pigment coated a statue a long time ago. Expose the statue, the painting, or anything else, to a concentrated beam of red light, then take a picture with a camera sensitive to infrared. While most of the art piece will be dark, anything painted with Egyptian blue will shine like animal eyes in the dark.
It's even better if you're a doctor. The frequency of infrared that Egyptian blue emits penetrates flesh more deeply than most other frequencies, without doing any damage. Incorporating Egyptian blue into medical technology will be a cheap way to scan a person's body. It won't take much Egyptian blue, either. Egyptian blue can be separated into sheets one thousandth the width of a human hair. How do get this advanced nanotechnology? Stirring the pigment gently in warm water for a few days. Which means that, it's possible to get a very cheap, very accurate medical technology out of a five-thousand-year-old pigment, some water, and a spoon.
Images: Walters Art Museum
[Via The Spatially Resolved Characterisation of Egyptian Blue, Chemistry of Glass, Egyptian Blue: The Color of Technology, Egyptian Blue: The Oldest Known Artificial Pigment, The Exceptional Near-Infrared Luminescence Properties of Cuprorivaite.]