Substantia. An International Journal of the History of Chemistry 2(1): 93-101, 2018 Firenze University Press www.fupress.com/substantia ISSN 1827-9635 (print) | ISSN 1827-9643 (online) | DOI: 10.13128/substantia-43 Citation: J. Ragai (2018) Snapshots of chemical practices in Ancient Egypt. Substantia 2(1): 93-101. doi: 10.13128/ substantia-43 Copyright: © 2018 J. Ragai. This is an open access, peer-reviewed article published by Firenze University Press (http://www.fupress.com/substantia) and distribuited under the terms of the Creative Commons Attribution License, which permits unrestricted use, distri- bution, and reproduction in any medi- um, provided the original author and source are credited. Data Availability Statement: All rel- evant data are within the paper and its Supporting Information files. Competing Interests: The Author(s) declare(s) no conflict of interest. Historical Article Snapshots of chemical practices in Ancient Egypt Jehane Ragai Emeritus Professor of Chemistry, The American University in Cairo, 37, Sedley Taylor road, CB28PN, Cambridge, UK E-mail: jragain@aucegypt.edu Abstract. This article gives a historical overview of a number of chemical practices carried out by the Ancient Egyptians and shows that beyond being purely empirical, in more than one instance their methods suggest an understanding of the rudiments of modern day chemistry. A close analysis of some of their preparations indicates that Ancient Egyptians were familiar with the principles of oxidation and reduction, could control the pH of a solution and were successful in preparing novel compounds through a controlled technology of chemical synthesis. In the latter endeavor it is shown that these Ancient people embraced the scientific method, preceding Aristotle’s rejection in Ancient Greece of a purely deductive approach to scientific enquiry. Egyp- tian Blue, the only pigment synthesized by the Ancient Egyptians is also discussed, and attention is drawn to its potential future contributions to modern high-tech applica- tions. Keywords. Ancient egyptians, chemical synthesis, Egyptian Blue, Kohl, scientific meth- od. “..It appears that Egyptians have developed a tech- nology of chemical synthesis in solution that allowed preparations of original compounds..” Phillip Walter 1 INTRODUCTION The embryonic stage of modern chemistry “Alchemy” can be traced back to Ancient Egypt, where Hermes Trismegistus2 said to be a contemporary of Moses, founded the art of Alchemy often dubbed the Hermetic arta. To many the words Alchemy and Chemistry are linked to “Khema” or “Chemi”3 which referred to the ancient name for Egypt meaning the black land. On the other hand Plutarch attributes the name “Alchemy” to the Ancient Egyptian activities, referring to their skills in the extraction of met- als, the preparation of alloys, and the working of gold4-6 all of which contrib- uted to the practical part of Alchemy. Today an observer reflecting on the achievements of the Ancient Egyp- tians, would certainly recognize a flurry of activities that could be referred 94 Jehane Ragai to as ‘Chemical’, which not only served their Religious beliefs but also had utilitarian, aesthetic, and symbolic connotations. It is generally believed that such accomplishments resulted from purely empirical observations. However the question remains: did the Ancient Egyptians at any point grasp the chemical significance of some of these practices? In what follows snapshots are provided of some of the most impressive ‘Chemical’ achievements of the Ancient Egyptians, the origins of which can in many cases be traced back to their religious convictions. RELIGIOUS BELIEFS AS CATALYSTS FOR CHEMICAL ACTIVITIES In Ancient Egypt an almost obsessive horror of death and extinction was reconciled with an absolute faith in immortality. To ensure eternal life, it was essential that the body be preserved in a good condition and that the tomb of the deceased be equipped with implements, stuffed ani- mals, donations, jewelry (in case of the rich and power- ful)… that would serve the deceased in the afterlife. Corpses as early as the third millennium BC were pre- served by a special technique of embalming (referred to as mummification) where the chemical process of osmo- sis played a crucial role. The main purpose of mummifi- cation was the dehydration of the body so as to prevent anaerobic bacteria from living on its tissues, causing their putrefaction and decay. It is very probable that the Ancient Egyptians did not understand the chemistry behind the phenomenon of osmosis but must have been aware, on a purely empir- ical basis, of the special role of natron (a mixture of sodi- um carbonate, bicarbonate with very small amounts of sodium sulfate and sodium chloride) in this dehydration process. It is of significance that Herodotus and Dio- dorus used the same word for preserved fish as that for mummy, considering that even in pre-mummification times, salt was used to dry fish.7 With bodies placed on a slanting board and covered with dry natron for forty days, fluids flowed readily by osmosis from inside the body through the skin and to the outer high concentration of natron, resulting in total dessication. Bodies were preserved by such a chemi- cal process and satisfied the Ancient Egyptians dreams of immortality as well as their strong belief in the great beyond8. The precise methods of mummification varied from period to period, and also within the same period depending on the social status of the dead person. THE TOMB: A PROMISE OF ETERNAL LIFE With the onset of the Dynastic period (~3300BC) Egyptians built elaborate tombs which housed, pro- tected, and equipped their dead for the afterlife. Initially built as a flat-roofed, rectangular structure: the ‘Masta- ba’, which included a shaft that led to an underground burial chamber, would soon give way to the pyramidal structure of the Giza pyramids (erected around ~2600- 2500 BC). A special mortar was used as a binder to sta- bilize the heavy limestone blocks that formed the core and outer layers of these massive constructions. Alfred Lucas7 in his pioneering work on Ancient Egyptian mortar, asserted that before Graeco-Roman times, the mortar employed for stone in Ancient Egypt was mainly ‘gypsum’. Some writers on Ancient Egypt have described Ancient Egyptian mortar as burnt lime, however, chemi- cal examination by Lucas7 has shown that Ancient Egyp- tians never used lime until the Roman periodb. Such results were later corroborated by Coppola and co-work- ers 9 who analysed mortars belonging to the Ramesside era and found that they all had a gypsum based binder. When heated at temperatures as low as 110°C-160°C gypsum loses water to produce the powder, plaster of Paris (CaSO4·½H2O) according to the reaction: 2CaSO4·2H2O —→ 2CaSO4·½H2O + 3H2O and when water is added to the powder of plaster of Par- is it rehydrates (absorbs water) and hardens rapidly. 2CaSO4·½H2O +3H2O → 2CaSO4·2H2O According to Coppola, Ancient Egyptian workers seemed to be conscious of the fact that the quality of the raw materials and methods of firing influenced the nature of the final product9. There is no doubt that the Ancient Egyptians rec- ognised on a purely experimental basis the deceptively simple chemical reactions involved in the preparation of gypsum. They also most likely understood that lime mortar entailed the formation of calcium oxide (CaO or quicklime) with the subsequent formation of Ca(OH)2 (slaked lime) to give mortar. CaCO3 + heat → CaO + CO2 and CaO + H2O → Ca(OH)2 Even though lime mortar could have been used in their constructions, they probably realized that the prep- heat 95Snapshots of chemical practices in Ancient Egypt aration of CaO, requiring a heating temperature close to 900 °C, was not an ideal choice. According to Lucas the scarcity of fuel in Ancient Egypt and the low tempera- ture processing of gypsum undoubtably must have been the reason why Ancient Egyptians preferred gypsum over lime. It is very probable that the process of preparing a suitable mortar had to be learnt by multiple trials, the results being gauged by the nature of the final product. Members of the ruling class and nobles were par- ticularly meticulous in preparing their tombs and strived to ensure that all their needs for the afterlife were addressed. Metallic implements, small copper and bronze statuettes representing a variety of deities, color- ed faience, glass amulets and shawabtis (small statuettes generally 365, that would serve the deceased every day of the year), intricate jewelry… all had to be scrupulously prepared and securely buried with the deceased. The skill for the production of burial implements and accessories, was generally attained through experi- mental observations, but may have necessitated a certain degree of primitive chemical knowledge. COPPER AND BRONZE: THE BEGINNING OF A STRONG TRADITION OF METAL WORKING It is only through heating the copper ore in the pres- ence of carbon (charcoal) as reducing agent that, as early as the Old Kingdom (~2600 BC), a successful extraction of copper could be achieved in Ancient Egypt. The ore basically in the form of malachite (basic copper carbonate) was crushed into small pieces and heated, in the presence of charcoal, to temperatures beyond 10000C (reached at by means of blow pipes or foot bellows) changing at first to copper oxide and then to molten copper. CuCO3.Cu(OH)2 → 2 CuO + CO2 + H2O C + CuO → Cu + CO It would take a thousand years after that discovery for bronze (an alloy of copper and tin) to enter into extensive use in Ancient Egypt. A wide spectrum of statues, imple- ments, weapons made out of this alloy were all buried in the tombs. As there are no tin ores in Egypt, it has been suggested that the tin was probably imported from Persia and possibly brought in by Phoenician traders10. The Egyptians would soon realize in their prepara- tion of bronze, that the melting point of copper could be lowered by alloying it with tin, an observation which would prove handy in many instances. Both the extraction of copper and the preparation of bronze seem to have been achieved through trial and Figure 1. The Kephren Pyramid in which gypsum mortar was used. Figure 2. Interior of a tomb. Figure 3. Extraction of Copper (malachite mixed with charcoal heated with blowpipes and then pouring of the molten copper as shown on the left). 96 Jehane Ragai error with the results embodied in empirical observa- tions which were methodically recorded and strictly fol- lowed. GOLD: FROM RELIGIOUS STATUARY TO LEGENDARY JEWELRY Identified with the sun god Ra and with the dazzling solar light, gold occupied a very special place amongst Ancient Egyptian metals. Its shine and glitter also made it quite attractive for use in ornaments and jewelry. The successful preparation of bronze would pave the way for the progress Egyptians would attain in working gold, namely in relation to the successful soldering of intricate pieces of gold jewelry. As judiciously pointed out by Cyril Aldred: There seems little doubt that ancients soldered their goldwork by the process known as colloidal hard soldering. In colloidal hard soldering, ground copper carbonate, probably in ancient Egypt in the form of powdered malachite so commonly used as an eye-cosmetic, is mixed with gum or glue and this adhe- sive is employed to stick the grains or wire into place, or to coat the adjacent edges of the parts to be joined…11 After heating and gradually increasing the tempera- ture from 100°C to 880 °C, … at about 880°C … the gold in contact with the copper melts to form a welded joint, whereas both gold and copper melt at nearly the same temperature well above this point, viz. 1083°C and 1063°C respectively. 11 This lowering of the melting point of both Copper and Gold was, as mentioned earlier, certainly inspired by bronze making. There is no recorded evidence, however, that the Egyptians had grasped the underlying chemical principle that governs such a phenomenon (lowering of the chemical potential etc…..) as we understand it today. EGYPTIAN BLUE: A REMINDER OF SUBLIME JUSTICE AND PERFECTION. Tomb walls were generally adorned with colored representations, mostly associated with deities, and symbolizing the sacred over the profane. Many of these depictions were painted in blue as to the Ancient Egyp- tians the blue color had a special significance. Worn on the breast plates of Egyptian priests, it was regarded as the color of Divine Truth. The blue colored war crown became very popular during the New Kingdom (~1500 BC) and was believed to confer upon its wearers, special protection from mysterious hostile forces.7 Lapis lazuli (most important component is lazulite of formula Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2.) and the natu- rally occurring blue pigment Azurite (Cu3(CO3)2(OH)2 a basic copper carbonate) were both known to the Ancient Egyptians. However, the rare occurrence of lapis lazuli and the pale blue color of the azurite pigment, encour- aged the Egyptians to produce their first synthetic pig- ment, the well known ‘Egyptian blue’b The earliest recorded use of Egyptian Blue is in the Old Kingdom (~ 2600-2100 BC) and its preparation con- tinued into the Greco-Roman Period (330BC-400AD)10 c Figure 4. Bronze statue of the Goddess Bastet. Figure 5. Gold Pectoral (parts soldered by colloidal hard soldering). 97Snapshots of chemical practices in Ancient Egypt The secret of its manufacture was lost in the fourth cen- tury AD, and rediscovered only in the nineteenth. The nature of this pigment has been extensively investigated12-15 and was found to be a calcium-cop- per tetrasilicate with the formula CaCuSi4O10 or (CaO. CuO.4SiO2) with a definite composition and crystal structure. Building on previous work and through their own attempts at preparing Egyptian Blue, Wiedemann and Bayer13 concluded that the raw materials had to be close to the stoichiometric composition 1 CaO, 1 CuO, 4SiO2 and that small amounts of fluxes (borax, salt) were needed to catalyse the reaction and to yield a bet- ter crystalline structure. It was also observed that in order to achieve a bright blue color the synthesis had to be carried out in an oxidizing atmosphere and at a tem- perature lower than 10000C. Even though it may never have been explicitly indi- cated, these results suggest that the Egyptians must have also been familiar with the rudiments of oxidation and reduction. Today Egyptian Blue is another important and fas- cinating legacy spawn by this Ancient Egyptian civili- zation with the recent observation that when irradiated with visible light, it fluoresces with exceptional strength in the near infrared region of the electromagnetic spec- trum 16-17. Such a property appears to have an important future in modern high-tech applications, ranging from special fibre optical systems for telecommunications18 , state-of-the-art high resolution biomedical imaging 19-22 luminescent fingerprinting dusting powder 23and secu- rity ink technology24. COLORED AMULETS: BESTOWING PROTECTION, HEALTH AND GOOD LUCK To match their magico-religeous beliefs the Ancient Egyptians fashioned small and beautifully colored objects (notably scarabs, amulets, ushabtis) made of a ware far better adapted that the rough clay, the so-called Egyptian Faience. Such a ware composed of a body(core) coated with an alkali-based glaze, gave the Ancient Egyptians the opportunity to produce a wide spectrum of colors. Until the XVIIIth dynasty (1550 – 1295 BC), blue faience was produced from the thermal decomposi- tion of malachite or azurite during the manufacture of the glaze (the color was mainly due to copper Cu in the Figure 7. Hippo Goddess (Taweret, goddess of childbirth) in blue faience. Figure 6. Preparation of Bronze (heating by means of foot bellows). 98 Jehane Ragai form of copper oxide CuO ). Ancient Egyptians would soon become aware that a prolonged exposure to high temperature would favor the green color over the blue.25 Caution therefore had to be exercised in the heating of the glaze and it was only during the Middle Kingdom (2055–1650 BC) that blue became common in faience. During the XVIIIth dynasty(c. 1550-c. 1292 BC), cobalt in the form of cobalt oxide (CoO) was the princi- pal colorant for blue faience and was generally accompa- nied by a significant amount of copper. An intense blue color was obtained with concentrations of CoO as low as 0.05 per cent which turned to violet or indigo when con- centration was increased to 0.2 percent. In the coloring of the glaze, the Egyptians realised, again probably on a purely empirical basis, that the colors exhibited by metal oxides in minerals could not always be transferred to the vitreous state. In view of the ligand field and crystal field effects, rarely does a transi- tion metal in glass have the same chemical environment as in a mineral. Amulets in the form of the Ankh sign (the key of life), the Eye of Horus, or the scarab, were often depicted in blue and were worn by the Egyptians and also buried with their mummies providing protection and prosperity. Here to the symbolism of color (blue) was added the symbolism of form (amulet). EYE MAKEUP: A VEHICLE TO GOOD HEALTH AND IMMORTALITY Makeup occupied a primary position at all levels of Ancient Egyptian society and played an important role in funerary rites for the purification of the body26. Beau- ty symbolised holiness – a key to the attainment of eter- nal life – and eye makeup in particular had an impor- tant standing in the Ancient Egyptians’ collection of cosmetic elements. A close connection was perceived between the madeup eye, the lunar cyclical renewal and the clash between the gods Horus and Set26. According to one myth, Set gouged out Horus’s eye in a battle, an event perceived by the Egyptians as an interruption of the usual lunar cycle and a threat to the return of the new moon27. For the reestablishment of the cosmic order the eye had to be reconstituted and cured – a task success- fully achieved by Thot the God of writing. Philip Walter referring to the rehabilitation of Horus’s eye points out that.. …The eye of the God should… be completed, reconsti- tuted with makeup and unguents to ensure by the benefi- cial power of cosmetics the integrity and the health of the Divine eyes, and the victory of the Light. 28 The Eye of Horus adorned with makeup came to symbolise the moon with all its powerful and protective connotations. Ancient Egyptian religious texts attest to its primary symbolic role and importance: Take two eyes of Horus, the black and the white, take them to your forehead that they may illuminate your face…29 Such beliefs led the Egyptians to regularly use eye makeup during their lifetime. They also ensured that upon their death and as a vehicle to good health and immortality, containers holding cosmetic powders would be included in their burial surroundings . KOHL AND THE PRACTICE OF WET CHEMISTRY The 1798 Napoleonic expedition to Egypt brought back a large number of these powders preserved in ala- baster, ceramic, wood or reed jars dating from 2000 B.C., the latter have been kept in the storage rooms of Louvre’s laboratories.26,30 Amongst these were two forms of eye makeup used since predynastic times: the green eye paint prepared from the mineral malachite which was usually applied to the lower eyelids and the black makeup, known as Kohl, generally used for the upper lids. In 1995, a group of French scientists led by chem- ist Philip Walter started researching these Ancient Egyptian cosmetics through a collaborative partner- ship between the CNRS (National Center for Scientific Research), the Louvre Department of Egyptian Antiq- uities and the Scientific laboratories of l’Oreal. The col- Figure 8. The eye of Horus. 99Snapshots of chemical practices in Ancient Egypt laboration lasted close to seventeen years and part of the work entailed the analysis of black Kohl26. Using scanning electron microscopy in conjunction with X-ray diffraction for structural characterisation and phase identification, Walter and co-workers identi- fied two ores of lead namely galena and cerussite (PbS and PbCO3), but to their great surprise the analyses also revealed the presence of copious amounts of laurionite (Pb(OH)Cl) and phosgenite (Pb2Cl2CO3)31. In view of their very rare presence in nature and their copious amounts in the cosmetic vials, it was con- cluded that these minerals must have been artificially produced. The excellent state of preservation of the con- tainers ruled out any possibility of weathering or altera- tion effects. For comparative purposes Walter and co-workers prepared these lead compounds by stirring lead oxide (PbO litharge) with rock salt (NaCl) in carbonated free water to give laurionite (Pb(OH)Cl) and by adding to the mixture natron (mainly Na2CO3 and NaHCO3) to obtain phosgenite (Pb2Cl2CO3). In both cases the pre- pared minerals were very close in composition and tex- ture to the archaeological compounds32. To avoid the undesirable formation of hydroxides the reactions taking place (equations 1 and 2), seemingly quite simple, had to be closely monitored as a neutral pH needed to be maintained. PbO + H2O + NaCl → Pb(OH)Cl + NaOH [1] PbO + H2O + NaCl + 1/2Na2CO3 → 1/2 Pb2Cl2CO3 + 2 NaOH [2] Such a preparation therefore entailed the repeated addition of fresh water and sodium chloride and the continuous removal of the supernatant liquid. The pro- cess required several weeks to reach completion31. As pointed out by Patricia Pineau, director of research communication for the cosmetics giant L’Oreal: Without knowing much chemistry, how did they have the foresight to know that a chemical reaction started on one day would produce such and such a result after several weeks?30 This discovery led to the astonishing revelation that the Ancient Egyptians were in fact quite versed in the rudiments of wet chemistry, a practice which enabled them to synthesise original compounds in solution. The question remained: why did the Ancient Egyptian add these preparations to their eye makeup? Old manuscripts indicated that eye cosmetics ”… were essential remedies for treating eye illness and skin ailments…”32 and the Ancient Egyptian Ebers medical papyrus mentioned Kohl for the treatment of a plethora of eye diseases33. Intrigued by this situation, the French scientists Amatore, Walter and co-workers embarked on a project to find out if lead compounds had indeed any thera- peutic effects. Using ultramicroelectrodes they showed that submicromolar concentrations of Pb+2 generated by the partial solubility of laurionite (Pb(OH)Cl) and added to human skin cells led to the production of NO, a molecule which played a role in the body’s immune response.32 Commenting on such findings Martin Oliver from McGill university suggested that the released nitric oxide could either stimulate the immune cells present in the eye or alternatively kill the disease-forming bacteria close to the eye34 . It is therefore possible that the Ancient Egyptians realised on a purely empirical basis, that whenever a white paste (identified today as laurionite or phosgen- ite) was present in the eye makeup preparation, it would have a therapeutic effect on its bearers and would give them greater immunity. This observation may have been the driving force behind this specific synthesis32 . According to Bernstein such an activity “….remains the first known example of a large scale chemical process’’ in Ancient Egypt35 ! SOME REFLECTIVE COMMENTS Having dwelt at length upon some of the fascinating ‘Chemical’ accomplishments of the ancient Egyptians, it is now perhaps prudent to examine more closely the role of empirical probing as opposed to rational thinking and quantitative speculation in the chemical endeavors of these remarkable people. Almost a century ago, L.E. Warren referring to the Ancient Egyptians chemical practices expressed the fol- lowing opinion: It should be understood that the Egyptians in general did not possess an inquiring mind and that ordinarily they would not conduct experiments merely for the purpose of satisfying curiosity or gaining knowledge… 36 More recently Wledemann and Berke14, with regard to Egyptian Blue and other Ancient Egyptian chemical activities, suggested that: …Man-made blue pigments required sophisticated chemi- cal and technological developments… Ancient chemical achievements could not be based on atomic or molecular grounds. Therefore any progress was established by long and tedious processes of empirical probing14 100 Jehane Ragai There is no doubt that many of the Egyptians accomplishments, some of which are described in this text, must have come as a result of long and laborious experimental scrutiny and elaborate processes of empiri- cal trials. However when one considers Egyptian blue, the rigorous stoichiometric requirements and the specific conditions for its preparation (oxidizing atmosphere, addition of a small amount of catalytic flux, temperature control)13, must have no doubt involved some degree of quantitative speculation and rational thinking. Fur- thermore, the idea in itself of preparing one of the first known synthesized pigments, suggests the Ancient Egyptians’ ability to innovate and think creatively. The same is true with regard to the synthesis of the new compounds laurionite and phosgenite using “wet chemistry” in which the acidity had to be controlled over several weeks, and the alkaline supernatant liquid con- tinuously removed with the attendant addition of salted water. This certainly entailed quite an elaborate empiri- cal process but also reflects an activity which is implicit- ly intermingled with sound knowledge and which is not totally devoid of any rational speculation. With regard to the synthesis of phosgenite, Philip Walter suggested : We might presume that the observation of natural phenom- ena may have enabled them to develop and invent such a science. Due to the regular flooding of the Nile and the presence of the desert, Egypt is a country that offers oppor- tunities to observe a large number of mineral formations of exceptional character, especially around the salt lakes of the Wadi Natrun which supplied the natron so necessary to mummification. These carbonates of sodium are produced by chemical reactions between the salt water of the lake and the limestone substrate of the lake bottom, following very similar mechanisms to those involved in the making of the synthetic constituents of cosmetics…28 It can be therefore be surmised that the Ancient Egyptians in their synthesis of phosgenite applied a ver- sion of our modern day scientific method. Assuming that they observed as suggested by Walter the natural forma- tion of this compound, this would then have led them to hypothesise, as an informed guess, the needed conditions for a successful preparation, followed by testing through carefully controlled and replicable experiments (control of the acidity through continuous washing…) and ultimately verifying the validity of their hypothesis and checking whether or not it needed modification (obtaining a white compound with immunological effects..). This should not come as a surprise to us since according to the Edwin Smith papyrus there are indeed indications that the Ancient Egyptians had a rational approach to medicine in which they applied the present day scientific method37,38. The chemical practices of the Egyptians stand in partial contrast to Plato’s deductive mode of thinking where pure reasoning was the only route to knowledge at the total exclusion of experimental verification. There is no doubt that the Egyptians’ manufacture of these artificial lead–based compounds reflects an inductive approach very much in keeping with our modern scien- tific mode of inquiry! NOTES a) “Hermeticism, also called Hermetism is a reli- gious, philosophical, and esoteric tradition based pri- marily upon writings attributed to Hermes Trismegis- tus39. According to the ‘Hermetic view’ man can share in divinity and is therefore at least potentially in con- stant communication with God. The notion of a mystical ascent to the good acts as a unifying theme in ‘Hermet- ism’. b) Other pigments used in Ancient Egypt were mostly natural minerals. When working in 1980 as a chemical consultant to’ The Sphinx Project’ at the American Research Center in Egypt (ARCE), I analysed by X-ray Diffraction some blue pigments which were extracted from a cache in the front paws of the Sphinx. 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