Egyptian Blue
Coloured pencils were a treasure in my childhood; cheap and nasty ones that left pale streaks of colour on the paper or broke as soon as you pressed more heavily were easy to come by, but real quality pencils were expensive and only to be used for special occasions like school work (what a waste!) or making birthday cards for important people like uncles and aunties. Part of the pleasure of using them, of course, stemmed from the names block-printed on the shaft of the pencil in gold letters. These names were far more dignified than simple "red", "blue" or "yellow". Instead there were evocative names like "Chinese White", "Tuscan Red", "Umber" and "Burnt Sienna". I knew enough to be aware that Sienna was a city in Italy, but who burnt it and why, I longed to know.
Had I been a little more aware, I would have realised that these colours were to be found among the broken shards of pottery that littered the streets in India, where I grew up, for they are the earth colours that can be found in nature or produced by firing clay to differing temperatures. Curiously enough, yellows and greens are almost as easy to find: yellow ochre is from the earth and various plants or metals provide a range of green hues. The only colour which is not easily obtained from natural sources is blue.
Yet had I been an Italian artist around the time of Christ, my palette would have been enriched by the glowing "Egyptian Blue".
This is not to be confused with the vibrant blue paste that was used by Egyptian jewellers and which adorns the coffins of Tutankhamun. That particular colour came from lapis lazuli, a semi-precious stone which could be carved into bright blue ornaments or ground up to form a paste that could be moulded into intricate shapes. This, however, was a solution that only bespoke jewellers could adopt, for lapis lazuli comes from Afghanistan and it is mind-boggling to think of the tortuous route each piece of stone must have followed along the ancient trade routes of the eastern world. Certainly lapis lazuli would be far beyond the means of a struggling young artist in the garrets of Thebes and Memphis.
Yet the evidence from the tombs is clear that from about 2,000 BC Egyptian artists had access to a bright blue colour which they used profligately in their frescoes and on their statues. When Sir Flinders Petrie excavated at Hawara he uncovered an artist's workshop and still in place were the clay paint pots with residues of the colours still in the bottom of the dishes, including dribbles where he had dipped his brush.
This same blue colour turns up all over the ancient Middle East. It was used at Knossos and Mycenae, it decorated the temples of the Greeks and adorned the villas of the Romans, but then, about 900 AD the secret of its manufacture was lost. It reappeared to modern eyes in the excavations of Pompeii, and by sheer chance a chemist was on hand to document it.
The first indications that there were treasures hidden in the earth south of Naples came when workmen, digging a well, discovered a marble statue. The local landowner, intrigued at the possibility of adorning his villa with genuine (and free) classical statues, set his workmen to dig shafts off the bottom of the well and gradually they uncovered the first traces of the buried city. It became quite fashionable to visit the workmen as they toiled underground and Englishmen engaged on the Grand Tour made a point of stopping off in Pompeii where they could view the latest discoveries.
The workmen, for their part, welcomed the arrival of the visitors. Not only did they provide a diversion from the dusty task of clearing the tons of ash that had fallen on Pompeii, but any small finds that the workmen had made tended to change hands in exchange for gratuities, and no one ever objects to additional income!
Sir Humphry Davy, the great English chemist, visited Pompeii and records his impressions in his diary.
"In an excavation made at Pompeii, in May, 1814, at which I was present, a small pot containing a pale blue colour was dug up."
Like most of his contemporaries, Davy had received a classical education and may well have been aware of the tale told by Theophrastus, the Greek philosopher, who declared that Egyptian Blue had been invented by one of the pharaohs and was still being manufactured in Egypt. Vitruvius, a Roman architect, actually gave a lengthy description of how the colour was produced but attempts to follow his instructions had always failed - it now appears, because he accidentally (or intentionally) omitted a vital ingredient.
Davy was astute enough to realise that if he could discover the secret of this colour, he would have a ready market among painters and decorators. He managed to obtain a quantity of the colour contained in the pot, together with a few flakes of blue that he peeled off Roman frescoes with his fingernails, and took them back to London where he subjected them to chemical analysis. His conclusion was that the ingredients were lime, sand and copper.
Unfortunately, when he tried to combine these ingredients, he totally failed to recreate the vivid blue he had seen in Italy. Indeed, it was another 75 years before the French geologist Ferdinand Fouque solved the mystery. You needed quartz sand - the kind used to make glass, lime and a bit of copper plus some alkali. When heated to between 850°C and 1,000°C, you ended up with Egyptian Blue.
The alkali turns out to be the key ingredient. This may have been natron (the salt used for preserving mummies) or ash from burned organic material, but more likely it was an impurity in the particular sand that was used, (a fact which may hold the clue to the disappearance of the colour). Too much and you ended up with a lump of glass, too little and the colour simply didn't appear.
Modern analysis of the various shades of Egyptian Blue reveal another curiosity. Trace minerals are found which are typical of the various copper alloys of the period. This seems to indicate that the ancient paint makers bought up job lots of old bronze and used it for their paint; Vitruvius actually speaks of metal filings being added to the mixture. We can imagine the delightful picture of some bored apprentice being given the job of filing down a piece of discarded armour or the hand of a failed statue in order to make the precious paint.
Egyptian Blue varies in colour from a quite deep blue to the light blue noted by Sir Humphrey Davy, but it is unlikely that the ancient paint makers understood the reason for this variation. It all depends, apparently, upon the size of the crystals formed during the heating process. If the crystals were large, the colour was rich and dark, but if they were small, the colour was light. Thus the colour could be varied depending upon how finely you ground the pigment, a fact which must have exasperated artists who naturally wished to use the very finest pigments available.
Whether Egyptian Blue will ever make it back to the artist's palette of today is uncertain. Other easier and probably cheaper methods of producing blue have been devised. Perhaps the only advantage the colour still possesses is the fact that, as a silicate, it is extremely stable and does not fade, even in the Egyptian sun. The same cannot be said for many modern blues.
