Egyptian Blue

Egyptian Blue

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Egyptian blue is chemically known as calcium copper silicate (CaCuSi4O10 or CaO·CuO·4SiO2). It is a pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 used by Egyptians for thousands of years. It is considered to be the first synthetic pigment. The pigment was known to the Romans by the name caeruleum. Vitruvius
Vitruvius
Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....

 describes in his work '"De architectura
De architectura
' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus, as a guide for building projects...

" how it was produced by grinding sand, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 and natron
Natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

 and heating the mixture, shaped into small balls, in a furnace. Lime is necessary for the production as well, but probably lime-rich sand was used. After the Roman era, Egyptian Blue fell from usage and the manner of its creation forgotten.

The ancient Egyptian word wedjet
Wadjet
In Egyptian mythology, Wadjet, or the Green One , was originally the ancient local goddess of the city of Dep , which became part of the city that the Egyptians named Per-Wadjet, House of...

signifies blue, blue-green and green, and the same word is used for the human eye, and the protective Eye of Ra
Eye of Horus
The Eye of Horus is an ancient Egyptian symbol of protection, royal power and good health. The eye is personified in the goddess Wadjet...

.

The first recorded use of Egyptian blue as a color name in English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

 was in 1809.

Definition


Egyptian blue is a synthetic blue pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 made up of a mixture of silica, lime, copper, and alkali. Its color is due to a calcium-copper tetrasilicate CaCuSi4O10 of exactly the same composition as the naturally occurring mineral cuprorivaite. It occurs in Egypt during the 3rd millennium BC and is the first synthetic pigment to have been produced there, continuing in use until the end of the Greco-Roman period (332 BC–395 AD). The term for it in the Egyptian language is hsbd-iryt, which means artificial lapis lazuli
Lapis lazuli
Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

 (hsbd). It was used in antiquity (1) as a blue pigment to color a variety of different mediums such as stone, wood, plaster, papyrus, and canvas; and (2) in the production of numerous types of objects, including cylinder seals, beads, scarabs, inlays, pots and statuettes. It is also sometimes referred to in Egyptological literature as blue frit
Frit
Frit is a ceramic composition that has been fused in a special fusing oven, quenched to form a glass, and granulated. Frits form an important part of the batches used in compounding enamels and ceramic glazes; the purpose of this pre-fusion is to render any soluble and/or toxic components insoluble...

. Some have argued that this is an erroneous term that should be reserved for use to describe the initial phase of glass or glaze production while others argue that Egyptian blue is a frit in both the fine and coarse form since it is a product of solid state reaction. Its characteristic blue color, resulting from one of its main components—copper—ranges from a light to a dark hue, depending on differential processing and composition. Apart from Egypt, it has also been found in the Near East, the Eastern Mediterranean and at the limits of the Roman Empire. Although undoubtedly an Egyptian invention, it is unclear as to whether its existence elsewhere was a result of parallel inventions or whether its technology had spread to these areas.

History and background


The ancient Egyptians held the color blue in very high regard and were eager to present it on many media and in a variety of forms. They also desired to imitate the semi-precious stones turquoise
Turquoise
Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl648·4. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue...

 and lapis lazuli
Lapis lazuli
Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

, which were valued for their rarity and stark blue color. Use of naturally occurring minerals, such as azurite
Azurite
Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the type locality at Chessy-les-Mines near Lyon, France...

, to acquire this blue, was impractical as these minerals were rare and difficult to work. Therefore to appropriate the large quantities of blue color that the Egyptians sought, it was necessary for them to manufacture the pigment themselves.

The Egyptians developed a wide range of pigment variety including what is now known as Egyptian blue, which was the first of its color at the time of its development. This accomplishment was due to the advancement of Egypt as a settled agricultural society. This stable and established civilization encouraged the growth of a non-labor workforce, including clerics and the Egyptian theocracy. Egyptian pharaohs were patrons of the arts and consequently were devoted to the advancement of pigment technology.

The earliest evidence for the use of Egyptian blue is in the 4th Dynasty (c.2575-2467 BC), limestone sculptures from that period in addition to being shaped into a variety of cylinder seals and beads. In the Middle Kingdom
Middle Kingdom of Egypt
The Middle Kingdom of Egypt is the period in the history of ancient Egypt stretching from the establishment of the Eleventh Dynasty to the end of the Fourteenth Dynasty, between 2055 BC and 1650 BC, although some writers include the Thirteenth and Fourteenth dynasties in the Second Intermediate...

 (2050-1652 BC), it continued to be used as a pigment in the decoration of tombs, wall paintings, furnishings and statues and by the New Kingdom
New Kingdom
The New Kingdom of Egypt, also referred to as the Egyptian Empire is the period in ancient Egyptian history between the 16th century BC and the 11th century BC, covering the Eighteenth, Nineteenth, and Twentieth Dynasties of Egypt....

 (1570–1070 BC), began to be more widely utilized in the production of numerous objects. Its use continued throughout the Late period, and Greco-Roman period, only dying out in the 4th century AD, when the secret to its manufacture was lost. There is no written information in ancient Egyptian texts about the manufacture of Egyptian blue in antiquity and was only first mentioned in Roman literature by Vitruvius
Vitruvius
Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....

 during the first century BC. He refers to it as coeruleum and erroneously states that it was invented in Alexandria, and was made by mixing sand, copper filings, and natron
Natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

, failing to mention lime—a major component of Egyptian blue. Theophrastus
Theophrastus
Theophrastus , a Greek native of Eresos in Lesbos, was the successor to Aristotle in the Peripatetic school. He came to Athens at a young age, and initially studied in Plato's school. After Plato's death he attached himself to Aristotle. Aristotle bequeathed to Theophrastus his writings, and...

 gives it the Greek term κύανος (kyanos, blue), which probably originally referred to lapis lazuli. Finally, it was only at the beginning of the 19th century that there was a renewed interest in learning more about its manufacture when it was investigated by Sir Humphry Davy in 1815 and others such as W. T. Russell and F. Fouqué.

Composition and manufacture


Several experiments have been carried out by scientists and archaeologists interested in analyzing the composition of Egyptian blue and the techniques used to manufacture it. It is now generally regarded as a multi-phase material that was produced by heating together quartz sand, a copper compound, calcium carbonate, and a small amount of an alkali (plantash or natron
Natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

) at temperatures ranging between 800–1000 °C (depending on the amount of alkali used) for several hours. The result is cuprorivaite or Egyptian blue, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and water vapor:
Cu2CO3(OH)2 + 8 SiO2 + 2 CaCO3 → 2 CaCuSi4O10 + 3 CO2 + H2O


In its final state, Egyptian blue consists of rectangular blue crystals together with unreacted quartz and some glass. From the analysis of a number of samples from Egypt and elsewhere, it was determined that the weight percentage of the materials used to obtain Egyptian blue in antiquity usually ranged within the following amounts:
60–70% silica (SiO2)
7–15% calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....

 (CaO)
10–20% copper(II) oxide
Copper(II) oxide
Copper oxide or cupric oxide is the higher oxide of copper. As a mineral, it is known as tenorite.-Chemistry:It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen...

 (CuO)


To obtain theoretical cuprorivaite, where there are only blue crystals, with no excess of unreacted quartz or formation of glass, the following percentages would need to be used:
64% silica
15% calcium oxide
21% copper oxide

However none of the analyzed samples from antiquity were made of this definitive composition, as all had excesses of silica, together with an excess of either CuO or CaO. It has been suggested that this may have been intentional. An increase in the alkali content results in the pigment containing more unreacted quartz embedded in a glass matrix, which in turn results in a harder texture. Lowering the alkali content (less than 1%), on the other hand, does not allow glass to form and the resultant Egyptian blue is softer, with a hardness of 1–2 Mohs
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...

.

In addition to the way the level of the different compositions influenced texture, the way Egyptian blue was processed also had an effect on its texture, in terms of coarseness and fineness. Following a number of experiments, Title et al. concluded that for fine-textured Egyptian blue, two stages were necessary in order to obtain uniformly interspersed crystals. First the ingredients are heated, and the result is a coarse-textured product. This is then ground up to a fine powder and water is added. The paste is then reshaped and fired again at temperatures ranging between 850–950 °C for one hour. It is possible that these two stages were needed to produce a paste that was fine enough for the production of small objects. Coarse-textured Egyptian blue, on the other hand, would not have gone through the second stage. Since it is usually found in the form slabs (in the dynastic periods) and balls (in the Greco-Roman period) it is suggested that these could have either been awaiting to be processed through a second stage, where they would be ground and finely-textured, or they would have been ground for use as a blue pigment.

The shade of blue reached was also related to the coarseness and fineness of Egyptian blue as it was determined by the degree of aggregation of the Egyptian blue crystals. Coarse Egyptian blue, was relatively thick in form, due to the large clusters of crystals which adhere to the unreacted quartz. This clustering results in a dark blue color that is the appearance of coarse Egyptian blue. Alternatively, fine-textured Egyptian blue consists of smaller clusters that are uniformly interspersed between the unreacted quartz grains and tends to be light blue in color. Diluted light blue on the other hand is used to describe the color of fine-textured Egyptian blue that has a large amount of glass formed in its composition, which masks the blue color, and gives it a diluted appearance. It depends on the level of alkali added to the mixture and therefore the more the alkali, and thus more glass formed, the more the diluted appearance. This type of Egyptian blue is especially evident during the 18th dynasty and later and is probably associated with the surge in glass technology at this time.

If certain conditions were not met, the Egyptian blue would not be satisfactorily produced. For example, if the temperatures were above 1050 °C, it would become unstable. If too much lime was added, wollastonite
Wollastonite
Wollastonite is a calcium inosilicate mineral that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolostone is subjected to high temperature and pressure sometimes in the presence of silica-bearing fluids...

 (CaSiO3) forms and gives the pigment a green color. Too much of the copper ingredients results in excesses of copper oxides like cuprite and tenorite.

Sources


The main component of Egyptian blue was the silica, and it has been suggested that quartz sand found adjacent to the sites where Egyptian blue was being manufactured was its source, although there is no concrete evidence to support this hypothesis. The only evidence cited is by Jakcsh et al. who found crystals of titanomagnetite, a mineral found in desert sand, in samples collected from the tomb of Sabni (6th dynasty). Its presence in Egyptian blue indicates that quartz sand, rather than flint or chert, was used as the silica source. It would be interesting to compare this evidence with the evidence for the source of silica used for glass making at Qantir (New Kingdom Ramesside site), which is quartz pebbles and not sand.

It is believed that calcium oxide was not added on its own in the manufacture of Egyptian blue, but introduced as an impurity in the quartz sand and alkali. It is not clear from this then as to whether the craftsmen involved in the manufacture realized the importance of adding lime to the Egyptian blue mixture?

The source of copper could have either been a copper ore (such as malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

), filings from copper ingots or bronze scrap and other alloys. Prior to the New Kingdom there is scarce evidence as to which copper source was being used, but it is believed to have been copper ores. During the New Kingdom, there is evidence for the use of copper alloys, such as bronze, due to the presence of varying amounts of tin, arsenic, or lead found in the Egyptian blue material. Some have argued that the presence of tin oxide could have come from copper ores that itself contained tin oxide and not from the use of bronze. However, no copper ores have been found with these amounts of tin oxide. It is unclear as yet, why there would have been a switch from the use of copper ores in earlier periods, to the use of bronze scrap during the Late Bronze Age. It is possible that reserves had run out.

The total alkali content in analyzed samples of Egyptian blue is greater than 1%, suggesting that the alkali was introduced deliberately into the mixture and not as an impurity from other components. Sources of alkali could either have been natron
Natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

 from areas such as Wadi Natroun and El-Kab, or plantash. By measuring the amounts of potash and magnesia in the samples of Egyptian blue, it is generally possible to identify which source of alkali had been used, since the plantash contains higher amounts of potash and magnesia than the natron. However, due to the low concentration of alkali in Egyptian blue, which is a mere 4% or less, compared to glass, for example, which is at 10–20%, identifying the source is not always easy. It has been suggested, nonetheless, that the alkali source was natron, although the reasons for this assumption are unclear. On the other hand, analysis by Jaksch et al. of various samples of Egyptian blue identified variable amounts of phosphorus (up to 2 wt %), suggesting that the alkali source used was in actuality plantash and not natron. Since the glass industry during the Late Bronze Age used plantash as its source of alkali, there might have possibly been a link in terms of the alkali used for Egyptian blue before and after the introduction of the glass industry.

Archaeological evidence


Amarna: In the excavations at Amarna, Lisht and Malkata at the beginning of the twentieth century, Petrie uncovered two types of vessels that he suggested were used in antiquity to make Egyptian blue: bowl-shaped pans and cylindrical vessels/saggers. In recent excavations at Amarna by Barry Kemp (1989), very small numbers of these “fritting” pans were uncovered, although various remaining pieces of Egyptian blue ‘cake’ were found, which allowed the identification of five different categories of Egyptian blue forms and the vessels associated with them: large round flat cakes, large flat rectangular cakes, bowl-shaped cakes, small sack-shaped pieces and spherical shapes. No tin was found present in the samples analyzed, which the authors suggest is an indication that there was possible use of scrap copper instead of bronze.

Qantir: In the 1930s Mahmud Hamza excavated a number of objects related to the production of Egyptian blue at Qantir, such as Egyptian blue cakes and fragments in various stages of production providing evidence that Egyptian blue was actually produced at the site of Qantir. Recent excavations at the same site, uncovered a large copper-based industry, with several associated crafts, namely bronze-casting, red-glass making, faience production and Egyptian blue. Ceramic crucibles with adhering remains of Egyptian blue were found in the excavations, suggesting again that it had been manufactured on site. It is also possible that these Egyptian blue ‘cakes’ were later exported to other areas around the country to be worked as there was a scarcity of finished Egyptian blue products on site. For example, Egyptian blue cakes were found at Zawiyet Umm el-Rakham, a Ramesside fort near the Libyan coast, indicating that cakes were in fact traded, and worked at and reshaped away from their primary production site.

Connections with other vitreous material and with metals


Egyptian blue is closely related to the other vitreous materials produced by the ancient Egyptians, namely glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 and Egyptian faience
Egyptian faience
Egyptian faience is a non-clay based ceramic displaying surface vitrification which creates a bright lustre of various blue-green colours. Having not been made from clay it is often not classed as pottery. It is called "Egyptian faience" to distinguish it from faience, the tin glazed pottery...

, and it is possible that the Egyptians themselves did not employ separate terms to distinguish the three products from one another. Although it is easier to distinguish between faience and Egyptian blue, due to the distinct core of faience objects and their separate glaze layers, it is sometimes difficult to differentiate glass from Egyptian blue due to the very fine texture that Egyptian blue could occasionally have. This is especially true during the New Kingdom as Egyptian blue became more refined and glassy and continued as such into the Greco-Roman period. Since Egyptian blue, like faience, is a much older technology than glass, which only begins during the reign of Thutmose III (1479–1425 BC), there are no doubt changes in the manufacture of Egyptian blue that were associated with the introduction of the glass industry.

Analysis of the source of copper used in the manufacture of Egyptian blue indicates a relationship with the contemporaneous metal industry. Whereas in the earlier periods, it is most probable that copper ores were used, during the reign of Tutmosis III, the copper ore is replaced by the use of bronze filings. This has been established by the detection of a specific amount of tin oxide in Egyptian blue which could only have resulted from the use of tin bronze scraps as the source of copper, which coincides with the time that bronze became widely available in ancient Egypt.

Occurrences outside of Egypt


Egyptian blue was found in Western Asia during the middle of 3rd millennium BC in the form of small artifacts and inlays, but not as a pigment. It was found in the Mediterranean area at the end of the Middle Bronze age
Bronze Age
The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...

, and traces of tin were found in its composition suggesting the use of bronze scrap instead of copper ore as the source of copper. During the Roman period
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 there was extensive use of Egyptian blue, as a pot containing the unused pigment, found in 1814 in Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

, illustrates. It was also found as unused pigment in the tombs of a number of painters. Etruscan
Etruscan civilization
Etruscan civilization is the modern English name given to a civilization of ancient Italy in the area corresponding roughly to Tuscany. The ancient Romans called its creators the Tusci or Etrusci...

s also used it in their wall paintings. The related Chinese Blue has been suggested as having Egyptian roots.

See Also

  • Han purple and Han blue
  • Maya Blue
    Maya Blue
    Maya Blue is a unique bright azure blue pigment manufactured by cultures of pre-Columbian Mesoamerica, such as the Maya and Aztec.-Manufacture:...

  • Prussian blue
    Prussian blue
    Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

  • Ancient Chinese glass
    Ancient Chinese glass
    Ancient Chinese glass refers to all types of glass manufactured in China prior to the Qing Dynasty . In Chinese history, glass played a peripheral role in the arts and crafts, when compared to ceramics and metal work. The limited archaeological distribution and use of glass objects are evidence of...

  • List of colors

Further reading

  • Dayton, J. 1978, Minerals, metals, glazing & man, or, Who was Sesostris I? London: Harrap. ISBN 0-245-52807-5.

  • Lucas, A. & Harris. J.R. [1948] 1999, Ancient Egyptian materials and industries. Dover books on Egypt. Mineola, N.Y. : Dover. ISBN 0-486-40446-3.

  • Noll, W. 1981, Mineralogy and technology of the painted ceramics of ancient Egypt. In: M.J. Huges (ed.) Scientific studies in ancient ceramics. Occasional paper 19. London : British Museum, ISBN 0-86159-018-X.

  • Rehren, Th. & Pusch, E.B. & Herold, A. 1998, Glass coloring works within a copper-centered industrial complex in Late Bronze Age Egypt. In: McCray, P (ed), The prehistory and history of glassmaking technology. Ceramics and Civilization 8. Westerville, OH: American Ceramic Society. ISBN 1-57498-041-6

  • Riederer, J. 1997, Egyptian Blue. In: E.W. Fitzhugh, (ed.), Artists’ pigments 3: 23-45. Oxford university Press. ISBN 0-89468-256-3

  • Tite, M.S. 1985, Egyptian blue, faience and related materials: technological investigations. In: R.E. Jones & H.W. Catling (eds.) Science in Archaeology : proceedings of a meeting held at the British School at Athens, January 1985. London : Leopard's Head. ISBN 0-904887-02-2.

  • Wiedemann, H.G., Bayer, G. & Reller, A. 1998, Egyptian blue and Chinese blue. Production technologies and applications of two historically important blue pigments. In: S. Colinart & M. Menu (eds.), La couleur dans la peinture et lémaillage de l’Egypte Ancienne. Scienze e materiali del patrimonio culturale 4. Bari: Edipuglia. ISBN 88-7228-201-2.