This is the second in the Colours of Ancient Egypt series; if you want to start at the beginning, click here. 

The colour blue has already featured in a couple of posts in this blog (e.g. check out Cerys Jones’ post on why the Common Kingfisher looks blue) but it seems impossible to me to discuss colour, especially in Ancient Egypt, and not start with blue. Arguably, blue has the most interesting history of all the colours, which can be attributed to the fact that it is not a colour that appears much in nature – that is, if you exclude large bodies of water and the sky, obviously. Naturally occurring materials which can be made into blue colourants are rare and the process of production is often very time-consuming. In Ancient Egypt, pigments for painting and ceramics were ground from precious minerals such as azurite and lapis lazuli; indigo, a textile dye now famous for its use in colouring jeans, was extracted from plants.

Left: two pieces of azurite (Petrie Museum, UC43790); Right: lapis lazuli (Image: Hannes Grobe)

However, all the above-mentioned colourants presented issues which limited their use. Azurite pigment is unstable in air and would eventually be transformed into its green counterpart, malachite. Lapis lazuli had to be imported from north-east Afghanistan (still the major source of the precious stone) and the extraction process would produce only small amounts of the purest colourant powder called ultramarine. Finally, indigo dyes can fade quickly when exposed to sunlight.

And yet it seems that the Ancient Egyptians attributed important meaning to the colour blue and it was used in many amulets and jewellery pieces such as the blue faience ring, lapis lazuli and gold bracelet or the serpent amulet from the Petrie Museum collection (below).

From left to right: blue faience ring with openwork bezel in form of uadjat eye (Petrie Museum, UC24520); lapis lazuli serpent amulet (UC38655); fragment of bracelet with alternative zig-zag lapis lazuli and gold beads (UC25970).

Therefore, the race to artificially produce a stable blue colourant began rather early. In fact, the earliest evidence of the first-known synthetic pigment, Egyptian blue, has been dated to the pre-dynastic period (ca. 3250 BC)[1]. It was a calcium copper silicate (or cuprorivaite) and – although the exact method of manufacture has been lost since the fall of the Roman Empire – we now know that it was made by heating a mixture of quartz sand, a copper compound, calcium carbonate and a small amount of an alkali such as natron, to temperatures over 800°C.

Fragment of fused Egyptian blue (Petrie Museum, UC25037).

This resulted in a bright blue pigment that proved very stable to the elements and was thus widely used well beyond Egypt. In fact, its presence has recently been discovered on the Parthenon Marbles in the British Museum due to its unusually strong photoluminescence, i.e. when the pigment is illuminated with red light (wavelengths around 630 nm) it emits near infrared radiation (with a max emission at 910 nm).

After its disappearance, artists and artisans had to make do with natural pigments and, being the most stable and brilliant, ultramarine became the coveted colourant once again. In fact, during the Renaissance, it is reputed to have been more expensive than gold and, as a result, often reserved for the pictorial representations of the Madonna and Christ. And so, the search for another replacement was back on. But it wasn’t until the early 1700s that another synthetic blue pigment was discovered, this time accidentally, by a paint maker from Berlin who, while attempting to make a red dye, unintentionally used blood-tainted potash in his recipe. The iron from the blood reacted with the other ingredients creating a distinctly blue compound, iron ferrocyanide, which would later be named Prussian blue. Naturally, other man-made blue pigments and dyes followed, including artificial ultramarine, indigo and phthalocyanine blues.

However, it wasn’t quite the end of the line for Egyptian blue, which was rediscovered and extensively studied in the 19^th century by such great people as Sir Humphry Davy. And not only are we now able to reproduce the compound for artistic purposes, scientists are finding more and more surprising applications for its luminescence properties, such as biomedical analysis, telecommunications and (my personal favourite) security and crime detection[2].

References:

[1]  Lorelei H. Corcoran, “The Color Blue as an ‘Animator’ in Ancient Egyptian Art,” in Rachael B.Goldman, (Ed.), Essays in Global Color History, Interpreting the Ancient Spectrum (NJ, Gorgias Press, 2016), pp. 59-82.

[2] Benjamin Errington, Glen Lawson, Simon W. Lewis, Gregory D. Smith, ‘Micronised Egyptian blue pigment: A novel near-infrared luminescent fingerprint dusting powder’, Dyes and Pigments, vol 132, (2016), pp 310-315.

If you were to visit the Petrie Museum with infrared vision, you would probably be drawn to wildly different parts of the collection than you would normally. Certain artefacts would appear to glow before your eyes. This is because of the inventively-named pigment Egyptian blue, which, as the name tells you, is a blue pigment that was commonly used in Egypt. However, Egyptian blue has a special property that makes it stand out from the rest: when illuminated in visible light, it fluoresces infrared light. If you could see infrared light, you would see all of the artefacts that contain this pigment glowing. I haven’t yet evolved to have this special power, but I have a camera that does. This is a multispectral imaging system and is what my PhD research is focused on. Multispectral imaging involves capturing images of objects that are illuminated in ultraviolet, visible and infrared light to reveal features that cannot be detected by the human eye alone.

Last November, I captured multispectral images of this Egyptian mummy mask from the Petrie Museum. In the Petrie catalogue, it is described as a “linen-based cartonnage mask, painted with blue headcloth, white face, black brows, eye-borders and pupils, and red-edged yellow band around face.” This mummy mask would have placed over the mummified body to protect the deceased in the afterlife. The Petrie has several mummy masks in the collection, including some that are gilded with gold.

Late period cartonnage mask (Petrie Museum, 55084)

The mask was illuminated in visible light and an infrared filter was placed in front of the camera lens. This meant that only infrared light was able to pass through the lens and be captured by the camera. The resulting image is below. The blue headcloth appears brightly in the image, indicating that it is painted in Egyptian blue. We were also able to confirm that the little fragment of mask in the vial was also from the headpiece, as this also fluoresced.

The cartonnage mask illuminated in visible light (left) and captured with an infrared filter (right). (Photo: Cerys Jones)

When you search Egyptian blue in the Petrie catalogue, 194 results appear ranging from Egyptian blue scarab beetles to plaster with hieroglyphs written in Egyptian blue paint. Two of my favourite items from the collection are the Egyptian blue hippopotamus and the Egyptian blue paste amulet of a lion-headed goddess. The hippopotamus represents Taweret, the Ancient Egyptian goddess of childbirth and fertility. The lion-headed goddess is probably Bastet, the goddess of warfare in Lower Egypt .

Left, hippopotamus in Egyptian blue pigment (Petrie Museum, 6489) and right, Egyptian blue paste lion-headed amulet (Petrie Museum, 52875).

Next time you visit an Egyptian museum, keep your eyes out for any artefacts that are painted in Egyptian Blue that are glowing unbeknown to your eyes!