Todd McIntyre

Did I accidentally discover how to make Egyptian Blue? When I was demonstrating a scoop mark-making mishap last time, where everything went awry, @areoinfo asked an intriguing question upon seeing the pictures. Did I inadvertently stumble upon the secret to making the famed Egyptian blue paint? Good question! Well, let's see what came out of the kiln and if it even remotely resembles Egyptian blue. In the pictures below, we can see the famous Egyptian blue paint "at work." The Egyptians painted with this super, vivid dark blue for millennia until the secret of its production was lost. Despite producing several tons of it over the millennia, at some point, they could no longer make a single gram, and even the method of its production was forgotten. Of course, there are guesses about how it might have been made, and this will have significance later on, but for now, let’s look at my clumsy attempt to a completely different thing and its outcome. So, last fall, I went to a potter to try making scoop marks in his large kiln, using remnants of granite I had seen at a half-finished obelisk. The plan was to put my two granite slabs in the kiln (one black and one red granite), set a 10 cm tall iron pipe on them, and load the pipe with natron, which would melt at 851 degrees Celsius and carve out the granite underneath, creating the scoop mark. It couldn’t possibly fail, right? Well, it didn’t work out that way because the only spot where the melted natron didn’t erode my granite slab was exactly where the pipe stood with the natron inside. The melted natron escaped from under the pipe and eroded the granite everywhere else, except under the pipe, thereby creating a negative scoop mark. But more interesting was the change that occurred with the red granite slab. It turned blue. I swear I didn’t paint it blue; in fact, I didn’t do anything with it except what I described above: I put it in a kiln, added natron, and raised the temperature to 851 degrees Celsius. That’s all. Now let's look at the current official explanation for the production of Egyptian blue! I quote: “It is now generally regarded as a multiphase material that was produced by heating together quartz sand, a copper compound, calcium carbonate, and a small amount of an alkali (ash from salt-tolerant, halophyte plants or natron) at temperatures ranging between 800 and 1,000 °C (1,470 and 1,830 °F) for several hours. The result is cuprorivaite or Egyptian blue, carbon dioxide, and water vapor.” Wow! This almost completely matches my experiment, except my source of quartz was the granite slab, and my source of copper was also the granite slab. There’s NO need for a separate copper source if the granite contains enough copper! The third component is calcium carbonate, which I substituted with natron, i.e., sodium carbonate, and the fourth component is wood ash, which I believe simply came from the contamination of charcoal used. Of course, I see that my blue isn’t exactly the same shade as Egyptian blue, but I didn’t use Egyptian red granite, rather some European variety. The composition of the two stones could differ enough that if we used Egyptian red granite, the blue might be bluer. Or who knows. And anyway, it’s still a long way from this to a usable paint; this is just the pigment. So, have I discovered Egyptian blue, or not? You decide!