CHEMISTRY and GRECIAN ARCHAEOLOGY* WILLIAM FOSTER Princeton University, Princeton, New Jersey
Since chemistry deals with the study of the composition, properties, and transformation of all material things, i t has innumerable applications in the arts and sciences. Thus, it has been of great service to archaology i n the identification and analysis of narwus kinds of material things with which the archreologist has to deal, such as glass and pottery, metals and alloys, pigments and dyes, ancient buildings and tombs, embalming materials, and manuscripts and inks. Moremer, chemistry aids in the remowal of corrosion from metals and alloys, and in the preservetion of museum specimens.
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HE writer's interest in chemistry as it relates to archgology dates back nearly a quarter of a e n tuty. In 1908 Dr. 0. S. Tonks, who was then preceptor in art and archzeology in Princeton University but now head of the art department of Vassar College, was interested in finding out the composition of the lustrous black glaze of Attic pottery, so he naturally sought the advice and h e l ~ of a chemist. Furthermore. for number of years I have served unofficially as chem: ist for the American excavations which have been carried on at Corinth under the direction of Dr. T. Leslie Shear, professor of classical archieology in Princeton University. Professor Shear is now Field Director of the American School at Athens and Director of the Agora Excavations, and we have charge a t Princeton of the investigation of chemical problems which call for solution from time to time.
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earth, which he classified as "manganese." According to Caylus, this substance baked red, but could be rendered black by an admixture of color or of other earths. Dr. John .Davy, in 1842, conducted a series of experiments and arrived at the conclusion that the glaze is "glass, colored by black oxide of iron, perhaps mixed with particles o f metallic iron." Davy suggested that it was fired in a "muffle kiln" and "equally defended from the fumes of the charcoal fire and the oxidating influence of common air." According to Bliimner, some investigators have advanced hypotheses that the black glaze might be graphite or magnesia, that it is an earth but not a metal, and that a combination of the oxides of iron and manganese may have produced the black. In summing up the work done up to the year 1879, he claimed that the real nature of the black color had not been determined. Fowler and Wheeler, in their book entitled "Greek Archzology" (1909), say: The nature of the glaze which is to be seen on the finished vase in both the black- and red-figured styles, and the methods of its application, raise puzzling questions about which there is as yet no general agreement.
Such was the situation when we began our investigations at Princeton. Experiments were first conducted to find out whether manganese is present as an essential constituent of the glaze, as claimed by some, or whether its presence is accidental. A fragment of a Greek vase weighing 51 grams was fused in a silver crucible with THE GLAZE ON GREEK POTTERY potassium hydroxide until the black glaze was removed. The Greeks produced pottery of a very high order The melt was cooled, and after appropriate preliminary from the standpoint and Numer- treatment it was tested for manganese by the ordinary Ous fine 'pecimens of black-figured and of red-figured methods, with negative results. These tests led to the vases have been Many generations of conclusion that manganese is not an essential constituscholars have come and gone since Attic vases were ent of the black glaze, first discovered, and the nature and composition of the In the second place, fragments of a vase were heated lustrous black glaze has been a subject for speculation with a mixture of sulfUTicand hydrofluoric acids until and discussion for a long time. The production of the the glaze was removed. After the was propvery lustrous, permanent! glaze was a erly treated, the manganese was determined by the trade secret of Athenians. Pottery with very delicate colorimetric method of Walters, i. e., by glaze has been unearthed at Corinth, but the glaze is oxidizing the manganese to permanganic acid by means not equal to that of Attic potter^, and it chips off. of ammonium persulfate. The amowlt of manganese, Caylus, in 1761, as a result of his investigations, calculated as MnO, was 0,06 per cent, The experi'Iaimed that the glaze was composed of a ferruginous ment was repeated with material taken from the body the vase, and the percentage of MnO was * Presented before the Division of History of Chemistry of the A. C. S. at the Denver meeting, August. 1932. namely, 0.06. 270
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The experiment was repeated with different samples of a vase, but in this case a diamond point was employed to remove the glaze. MnO to the extent of 0.04 per cent. was found both in the glaze and in the body of the vase. The small amount of manganese (about 0.05 per cent. of MnO) found in the glaze might very well have been accidental, for it is well known that ordinary clays and rocks containing iron usually contain more or less manganese. At this stage of the experiments it was suspected that the black glaze might be due primarily to ferrous silicate, so this hypothesis was tested by a number of carefully conducted experiments. I n a e r y case more ferrous iron was found to be present i n the glaze than i n the body of the pottery. In general, the glaze was removed by means of a mixture of sulfuric and hydrofluoric acids, care being taken to exclude the air. The iron was determined by oxidation with N/50 potassium permanganate. Due to the fact that the glaze could not be entirely freed from clay, it was impossible to determine the absolute amount of iron in t h e ferrous condition in the clay; but evidence enough was obtained to indicate that ferrous i7on is responsible for a t least part of the lustrous black of the decoratina- medium of Attic pottery. With these facts before us, Tonks conducted many experiments looking toward the synthesis of the glaze, and some of the results are very interesting. He says:' Not to be tedious by enumerating the number of trials I made before getting the desired result, I may say tbat it proved eventually tbat a combination of eight parts of nitrate of soda to one of clay, fritted together, and then mixed in the proportions of two parts of frit to one of ferrous oxide, produced a glaze identical with that on Greek vases.
It was reasonable to suppose that the red glaze contains more iron in the ferric condition than does the body of the pottery, and less ferrous iron in the glaze than in the body. This hypothesis was confirmed by experiment. The tests were made upon a fragment of a Mycenaean vase and the results were as follows:
black glazes is identical, and the researches of Tonks and Foster a t Princeton University in 1908-1910 fully established the thesis." They also call attention to the fact that the black glaze retains its color when heated to a high temperature with air excluded, but turns red when similarly heated in air. The idea by Binns and Fraser, at the outset, was the same as that upon which Foster and Tonks had worked, namely, that iron oxide was added to the glaze mixture in the ferrous condition. "There had been no thought of submitting the glaze itself to a reducing action in the firing. The endeavor was to use black oxide-blacksmith's scale was the usual form--and to prevent it from oxidizing in the kiln." The essential points of their study were, first, that the formation of the black color in the glaze took place in the fire and there only, and, second, that while the reducing fire also blackened the body, this was re-oxidized and reddened during cooling. They say: Evidently the process of firing was conducted by the Greeks on this plan: as soon as the kiln attained a visible red color. or at about 600°C.,a tYDe of fuel which would produce a dense smoke was used. This was continued until the finishing temperature' of about 950'C. was reached. The cooling was then allowed to proceed very slowly and with a smoky atmosphere down to about 850°C..at which point the air was freely admitted but still with slow cooling. The glaze having become glossy in the fusion, the black iron oxide was locked in and could not change. The body, however, which had also been blackened was, in its porous condition, able to re-absorb the necessary oxygen and to recover its red color.
This theory, according to Binns and Fraser, has been substantiated by simply reversing the process. The neck of a vessel of which the body was gray throughout was broken, and one of the pieces was heated in air to 80O0C.,whereupon the gray was changed to red, but the glaze was not affected. When a second piece was heated in air to 950°C., the glaze softened and as a result of oxidation changed to a chestnut brown. METALS AND ALLOYS
The use of gold and copper dates from prehistoric times, and it is probable that these were the first metals used by man. In Egypt the extraction and use of copper can be traced back to about 3500 B.C., or Glme Bodr of Vela Ferrous imn (Re01 0.44% 0.56% shortly before the first dynasty. Stone weapons and Ferric imn (F-0:) 8.18% 7.36% implements were stii in common use. As a rule, After allowing for ferrous iron, the red glaze was ancient gold is alloyed with silver, the latter metal havfound to contain considerably more ferric iron than ing been known since a t least 2000 B.C. Gold coins did the body of the pottery. nearly 2500 years old have recently been found in the Charles F. Binns and D. D. Frasera of the New York ruins of Sardis, the ancient capital of Lydia; they were State School of Clay-Working and Ceramics, Alfred coined during the reign of Croesus. According to J. University, have recently made a study of the genesis of Newton Friend, iron was known in Egypt in predythe Greek black glaze. nastic time, perhaps 4000 B.C., although it was not in They say: "The ceramist has not as yet been able to common use until about 1300 B.C. Howard Carter reproduce precisely the color and surface of the decora- says: tion as it was applied to the vases by these artists." However short, however hazardous Tut-ankh-Amen's reign They also say: "As early at least as 1903, it was main- (1358-1350 B.C.),it marks an important point in Egyptian histained tory, for during that brief period of nine years iron was introduced - that the composition of Myceniean and Attic into Egypt-the greatest empire of the age of bronze. Upon ' Toms, Am. I.Archdogy, 12,424 (1908) BWNSAND FRASER, ibid., 33, 1-9 (1929).
his mummy was found a beautifully wrought dagger of iron; witb-
in that innermost treasury was a set of model tools of iron,placed there as if to record the introduction of that new and special metal into Egypt.
The invention of coinage by the Lydians was adopted by the Ionian cities of the coast, by Miletus, etc. An electrum coinage was current over all the Asiatic side of the Levant. The gold coin contained 130 grains. Lead is mentioned in the Old Testament: Herodotus tells us that in Asia in Persian times the Thou didst blow with thy wind, the sea covered them: they value of gold to silver was as 13:l. In Mesopotamia sank as lead in the mighty waters. (Ez.15:lO). bars of silver weighing 169 grains were in use, and ten Pliny points out a distinction between lead and tin. of these (1690 grains) passed for 130 grains of gold. An Lead was used by the ancient Romans for water pipes. electrum coin of the weight of a bar of silver passed Mercury was first described by Greek writers. Its for ten bars of silver. ability to dissolve other metals, such as gold and silver,. Crcesus, the last king of Lydia (560-546 R.C.) was was known before our era. A ring of tin has been dis- one of the picturesque and romantic figures of the covered which dates from 1450 B.C. ancient world. He was rich and powerful. "As rich The manufacture of bronze, an alloy of copper and as Crcesus," is a phrase common to English speech tin, dates from about 3000 B.C. The Bronze Age fol- and quite frequent in literature in reference to any exlowed the Stone Age and it began in Europe about 2000 cessive accumulation of wealth. B.C. The kings of Sardis had natural deposits of gold a t Garland and Bannister say: their threshold, so the city leaped into a position of world supremacy. The Lydians knew how to separate Previous to 1000 B.C.,all the chief useful metals were being worked by the Egyptians, and the only ores that are now of ex- gold from silver. On one occasion Crcesus sent 117 tensive industrial importance, and were then unknown, are zinc, ingots of precious metal to Delphi; four of these were nickel, and aluminium. refined gold and the rest electrnm. The Spartans sent agents to Sardis to purchase gold with which to enrich Gold, silver, copper, iron, and bronze are used in the statue of Apollo; Crcesus made them a gift of all works of art. Gold is noted for its beauty, durability, they asked. Many gold objects of exquisite workmanand plasticity; and molten bronze for its great fluidity. ship were produced in Lydia. Crwus introduced a Bronze was hardened, and fashioned into knife and complete reform of the Lydian coinage. He abolished razor edges of the utmost keenness. electrum and substituted coins of gold. Crcesus Brass, an alloy of copper and zinc, has been long in adopted the gold standard about 560 B.C. use, but is more modern than bronze. The word was In April, 1922, the Sardis Expedition in charge of used indiscriminately in the Old Testament, both for Dr. T. L. Shear uncovered thirty small gold coins copper and its alloys. known as "staters," presumed to be the first ever minted, and attributed to the reign of King Crcesus. COINAGE OF METALS The coins were discovered a t Sardis, in ancient Lydia, Coins are of great value to archzeologists, for they about sixty miles from Smyrna. The clay pot or give information needed in fixing the chronology of vase containing these coins was about 4.5 inches in ancient arts. There is a special branch of knowledge height and was found lying about two feet below the called numismatics (Latin, numismn, coin), which surface, a little to the north of the site of the temple of may be defined as the science of coins and medals. Artemis. The lightest of these gold "staters" weighed 8.00 A coin is a lump of precious metal of fixed weight, stamped with the mark of some authority. It is prob- grams and the heaviest, 8.094 grams. The total weight able that coins were invented by the Lydians. The was 241.535 grams, which gave an average weight of earliest coins were struck from electrum, an alloy of 8.051 grams. This shows that there was remarkable gold and silver, which was found in the bed of the river uniformity. The touchstone was employed in ancient times for Pactolus and in other rivers of Western Asia. Herodotus called this alloy "white gold," for it was of a testing gold as is done a t the present time. The Lydian light yellow color. Electrum usually contained 20 to stone is mentioned by Theophrastus and other ancient 25 per cent. of silver. The Greeks supposed it to be a writers. The mineralogist calls it basanite. I t is a separate metal, reckoned by them as having three- variety of siliceous or flinty slate, having a grayish or fourths the value of gold and ten times the value of bluish black color. When employed to test the purity silver. Ancient gold contained more or less silver, and of gold, the amount of alloy is indicated by the color the latter contained gold. The following analyses are left on the stone when rubbed by the metal. One of the Sardis coins was tested with the toucbof interest. stone, which indicated that the metal was 0.958 fine. ANALTSBS OF ANE~BNT EOWTUNMmEIcchrrm Gold Silvn It is of interest to add that Percy Gardner informs u: that "Greeks and Persians, like the Chinese of our days, would readily judge of the fineness of bar by touch, sound, and smell." Analyses of different samples vary, and copper is Shear, in 1922, had an assay made of a sample of frequently found associated with gold and silver. 0.991 gram of metal taken from a gold coin bought at
auction in Brussels. This coin was minted by Crcesus. After removing the foreign iron by means of a magnet, the following percentages were obtained:
The results were so gratifying that the apparatus was shipped to Corinth, where the work is carried on in the field. It is now being carried on a t Athens, where thousands of coins are being discovered. Iron............ 0.15 Gold............ 98.13 Silver ........... 1.80 Platinum........ 0.02 The new process of restoration may be applied to The assayqs (Ledous and Company, New York) stated various metallic objects. For instance, we removed the that the percentages of silver and platinum were ap- rust from an ancient Carthaginian razor of bronze, which made it possible to read the inscription. Several proximate, due to the small sample. bronze coins were often supported in a rack made of Shear says: It is probable that they [the coins] were buried shortly after copper gauze, which facilitated the work. A day, or they were minted, and it is possible that the occasion of the burial even less, was usually sufficientfor treatment, but some was the siege and capture of the city of Sardis by Cyrus and the bronze objects require several months. The current Persians in the year 546 B.C. At such a time of crisis and peril density must be kept low, usually 1 to 5 amperes per it is customary for cautious individuals to bury their treasures, square foot of surface. If the objects are delicate, the and at Sardis we h o w that it was largely done, for after his capture Crems advised Cyrus to prevent the victorious soldiers gassing must not be too rapid. The Greek bronze coins lay no particular claim to from pillaging the city, and promised if that were done, to urge the citizens to bring their wealth voluntarily and give to the artistic merit, but they have a high historical or archeoPersian king. logical value. As to types, there is usually an image of The types on the gold and silver coins of the reign an animal, or a bird, etc., on the coiu. The Corinthian of Crcesus are identical, namely, the heads of lion and coins are characterized by Pegasus, the winged horse. It is well known to arch~ologiststhat Corinthian bull facing each other on obverse, and on the reverse a double incuse square, produced by the anvil or punch coins are much more thoroughly corroded than are those of other Greek cities, such as Sicyon, but the reason in striking. The Greeks employed simple coinage implements for this difference has been a puzzle. A preliminary anvil, hammer, and tongs. A die was cut in intaglio, study of this problem has been made a t Princeton and in bronze, brass, or soft iron. Percy Gardner tells us some interesting facts have been discovered. First of all, the coins were analyzed by Dr. E. R. that the die was then let into a prepared hole in an anvil, a blank was cast and by means of tongs it was placed, Caley. In order to determine the true composition of while hot, on the anvil; on the coiu another bar was the alloys from which the coins were minted, the patina, placed into which a second die, or punch, had been in- or green rust, was removed. For quantitative analysis serted. One or more sharp blows were struck with each coin was divided approximately into halves and a hammer on top of the bar. So far as I know, no each part was analyzed. This division was made for Greek dies have come down to us, but a few Roman dies two purposes--one in order to serve as a check on the have been found. The dies were produced from soft analytical work and the other in order to see whether metal and soon wore out. We are told by experts that or not the given coin was uniform in composition. the artists who made dies were rapid and careless in their work. It appears that all dies down to the 5th Second Port century A.D. were cut by means of the wheel, just of Coin % as gems are cut. Graving tools were introduced in Tin 8.25 Roman times. There was real art in ancient coin-makLead 5.43 85.27 COPP~ ing. 0.28 Iron Siver was the standard currency of early Greece and Republican Rome; whiie in Asia Minor electrum and gold were the first standards. Bronze and copper were the early currency of Rome; they first appeared in Greece toward the end of the 5th century B.C. These coins were used for small change. I have seen some of the gold coined in the reign of It appears from these analyses that the Corinthian coin Crcesus and it is as bright and beautiful as it was when is less homogeneous in composition than is the Sicyon newly minted 2500 years ago. Silver corrodes more coin, which would suggest that it is more likely to coror less, due to the formation of black silver snK5de. rode, due to electrolytic effects when in contact with soil waters or moisture. The lead content of the Sicyon Bronze coins are often badly corroded. A fewyears ago Professor Shear brought from Corinth coin is much higher - than is that of the coin from Cornumerous coins which were so badly corroded that the inth. After the coins had been analyzed i t seemed wise to inscriptions could not be read. We removed the corrosion from them by the electrolytic method (Fink have them examined by an expert in the field of metallogprocess); that is, the coins were made the cathode in raphy and to have photomicrographs made. This was a 2 per cent. solution of sodium hydroxide, platinum done by my colleague, Professor D. P. Smith, and the being employed as anode. On passing a current of results were most interesting and important. The folproper density, hydrogen was generated on the cathode. lowing is taken from his report:
The bronze mins of Corinth and of Sicyon, when subjected to metallographic examination, exhibit marked differences. The Corinthian coin shows the unmistakable dendritic strueture (Figure 1) of an alloy which has been cast and not subsequently severely worked, while the coin from Sicyon displays the no less characteristic granular structure (Figures 2, 4, 6) of a bronze thoroughly worked after casting. Upon examination a t somewhat higher magnification, €he dendrites of the Corinthian bronze are seen to have recrystallized (Figure 3). This must have been brought about either by coldworking, followed by reheating t o a temperature above the recrystallization temperature, or by hot-working. But the amount of working must have been very small, since i t scarcely disturbed the original dendritism. The structure of this coin is, therefore, consistent with the supposition that a cast disc was reheated t o a dull red heat, or above, and a t this temperature stamped with the design. The micro-structure of the Sicyonian coin (Figures 4, 6) tells another story. Except for scattered masses of lead, seen as dark spots in the photograph, or as blurred areas which me cavities out of focus, this bronze consists of grains in which several systems of twinning bands may be detected. Most of these are of the broad type, annealing twins, indicating that the metal has been repeatedly hot-worked, or cold-worked with suhsequent reheating t o the softening temperature. Considered in conjunction with the complete destruction of the original dendrites, and homogenization of the alloy, which has taken place. this structure seems to show clearly that the metal was repeatedly hammered out. Finally, the lait system or twins t o be formed-since rarely intersected by the broader bands of the other systems--consists of very narrow hands, some 1 to 2 millionths of an inch broad, before magnification, which are S e M in many grains in Figure 6. These appear to be mechanical twins, formed by cold-work after the last reheating; for on annealing, they would doubtless grow to broader annealing twins. From all this we may conclude with much assurance that the Sicyonians made their coin by a method not dissimilar t o that employed in modem mints, the cast ingot being beaten out into a thin sheet. upon which the design was stamped. Whether the coins were cut from the sheet before or after the impression of the design. and how the cutting was done, cannot be said from the evidence here considered. I t may also he remarked that the indication that the striking of the design occurred a t a temperature below the softening point of the metal does not necessarily lead to the conclusion that the Sicyonians were possessed of dies made of steel, or of a similarly hard material. For the bronze of this coin, containing some 13 per cent. of lead, was exceptionally soft, and might have been stamped with a bronze of other and harder composition. Indeed, the idea rather suggests itself that the unusually high lead content may have been given t o the coinage metal for precisely this reason. The structure also appears to afford an explanation of the fact that the Corinthian coins are more severely corroded than are those of Sicyon. For the Corinthian bronze is extraordinarily inhomogeneous in respect t o chemical composition, and, as is well known, such irregularities produce local electrolytic currents which greatly intensify corrosion. I n the Sicyonian bronze, inequalities of composition h a w in great degree been relieved by the thorough working and annealing t o which the metal has been subjected, and the greater uniformity of the material is probably in large part responsible for its superior resistance to corrosion. The high lead content may be a contributing factor, but is seemingly a subordinate one, since the lead is distributed in nodules and isolated masses (Figures 2, 4) which do not envelope the grains of the bronze, or greatly hinder the access of corrosive agents. One characteristic of the Corinthian bronze seems to be unique. Filaments of a slag, or some similar glassy mineral substance, occur within the corn of the dendrites (Figure 5), and not between the latter, in the late-freezing masses of lead and other admixtures. Since foreign substances, which are insoluble in the metal, are in all ordinary cases rejected by the growing metallic crystals, regardless of whether the foreign material is
solid or liquid a t the temperatures a t which the metal freezes. the extraordinary position of these mineral cores will require much explanation. I n the present connection it has interest for the following reason. The mineral material is much harder than the bronze as may also be observed in Figure 5 where the mineral masses stand in bold relief above the metal which has been worn away in polishing the specimens. Moreover, the rocky masses, forming as they do the core around which the crystal has grown. are extremely firmly embedded, and do not readily tear out as they would do if they occupied the usual position of foreign materials, in the inter-dendritic regions. After slight abrasion this alloy provides itself with innumerable, minute, exceedingly hard bosses, projecting slightly from the surface, and it may be predicted with cofidence that its resistance to abrasive wear will be found t o be much greater than that of any ordinary bronze. It would he interesting t o know whether the presence of the mineral matter was wholly an accident, or whether the Corinthians had discovered that the addition of some hard mineral powder produced coins which were highly resistant to wear. If the latter w a s the case, they anticipated in principle some wellknown metallurgical inventions of recent years.
Before the Sicyonian coins were examined by Smith, it was generally believed by archieologists that all ancient coins were produced by casting the molten metal, after which the stamping was done. It now appears that the Greeks were familiar with the art of heating and cold-working metals so as to secure a homogeneous product; the coins were then struck without melting and casting the metal. It might be of interest to add that we recently examined a kind of "cement" which Shear brought back from Greece. This "cement" was employed in the 5th century A.D. for fastening together pieces of bronze. Chemical analysis proved that the surface of the binding material was basic lead carbonate, while underneath a fairly thick crust there was metallic lead. This metal was used, therefore, by the ancients in cementing or binding metals together, but in the course of about 1500 years a considerable part of the lead has been converted into carbonate. EARTH PIGMENTS AND COLORS
Our main literary sources for obtaining knowledge concerning pigments used by the ancients are Pliny the Elder (23-79 A.D.), a Roman admiral and naturalist who perished a t the destruction of Pompeii; and Vitruvius, an architect during the reign of Augustus. Some additional information also is obtained from Theophrastus. Then, too, we have the analyses of pigments which have been made by chemists, such as Egyptian pigments, pots of pigments unearthed a t Pompeii, Corinth, and elsewhere, and of the pigments found on Greek and Roman frescoes. The use of pigments or colors for decorative purposes began in the prehistoric period. Sir Flinders Petrie puts the date of this period in Egypt a t 8000 to 5800 B.C. The pigments used by the ancients were largely earth colors, such as the yellow and red ochres, terre nrerle (a green pigment-a compound of iron), copperbearing minerals, and naturally occurring vermilion (cinnabar). The minerals realgar and orpiment (sulfides of arsenic) also were available. The former is
FIGURE1.-CORINTHIAN COLN X 83 Showing dendrites, with faintly seen cores of slag. Dark areas of lead and other admixtures between the dendrites.
FIGURE4.-SICYONIANCOIN X 1000 Grains, showing several orders of twins
FIGURE 2.-SICYONIANCOIN X 215 Showing uniform granular structure, with large and small masses of lead scattered throughout.
FIGURE ~.-CORINT~IAN COIN X 650 Showing slag cores a t the centers of dendrites, and lead inclusions hetween dendrites.
FIGURE3.-CORINTHIANCOIN X 215 Showing granular structure within the original dendrites.
FIGURE G.-SIWONIANCOIN X I740 Showing narrow mechanical twins in broad annealing twins of earlier formation.
orange-red in color and the latter is yellow. In addition, charcoal (carbon) and black chalk were used as pigments. Drawings were made in charcoal and in red and yellow ochres by paleolithic man; for example, their drawings represent with some degree of perfection certain animals which are now virtually extinct in Europe, such as the bison. While these pigments are not as durable as carvings in stone, some are remarkably well preserved. The favorite color for glazed vessels produced in Egypt in prehistoric times was blne to green, obtained by the use of copper compounds. Later on, but at a very early date, the famous Egyptian blue was used. It was a synthetic product-a richly colored glaze, glass, or frit, containing copper. Cobalt blue was apparently used by ancient potters, but not by painters until a comparatively recent date. Ultramarine, a pigment produced from lapis lazuli, the most famous of all blues, was not used in ancient times, but was a favorite color with mediaeval painters. Prehistoric slate palettes and mullers for rubbing down pigments have been discovered. The pigments were no doubt rubbed down with a medium. Many of the Etruscan frescoes are famous and very beautiful, as also are those in the palace of Knossos, in Crete. This wonderful palace was probably decorated abont 1500 B.C.; the pigments used were yellow and red ochres, black chalk, Egyptian blue, and lime for white. I t is probable, therefore, that there were commercial relations between Egypt and Crete when the palace of Knossos was decorated. Excavations now in progress unearth pigments used in classical times. For several years Shear has been uncovering a theater at Corinth. Of the remains discovered in this theater, the earliest date from abont 350 B.C. As a result of these excavations it is known that the Corinthians were acquainted with certain mineral pigments or colors. One of the most interesting discoveries made in the theater district in 1926 was a rude, bowl-shaped clay pot containing a red pigment. This pot was uncovered at a depth of 5.25 meters, in the sanctuary of Athena Chalinitis, which adjoins the theater. The pot does not resemble any Greek pottery of Corinth, and the clay of the vase is not of the Corinthian type. It appears, therefore, that the vessel was imported from some place where such crude ware was still being manufactured several hundred years before the beginning of the Christian era. I have analyzed a specimen of the contents of the pot and found it to be realgar (Arabic rehj-alghar, meaning powder of the mine or cave). This mineral occurs in nature; it is a sulfide of arsenic (Ass). Realgar was known in the days of Aristotle. According to evidence found in early writings, it seems reasonably sure that realgar has long meant the same as Greek ~W6orpiLKq and Latin sandaraca. Theophrastus, successor to Aristotle in the Peripatetic school, says that realgar was a red color used by painters; and Pliny states, on the authority of Juba, that it occurs on the island of Topaz
in the Red Sea. I t was perhaps found in many places. According to Strabo, Greek geographer and historian, realgar was mined in shafts near the city of Pompeiopolis, Paphlagonia, near Sinope; and the mines were worked by slaves and condemned criminals. The working conditions were hazardous, and Strabo says that poisonous vapors arose from the earth. This appears to be very doubtful. I t is probable, as thought by Bliimner, that the ill effects were due to fine dust which was inspired by the laborers. According to Aristotle, horses and other beasts were killed by the administration of uorv8upb~q; and Galen, a Greek who became the imperial physician a t Rome, recommended that it be mixed with butter and used as a poison for scorpions, very much as arsenic preparations are now used in orchard and garden to kill lowly forms of life. In this connection it is of interest to know that there is an arsenic mold (penicillium breericuule) which by its action on certain wall-papers is said to produce a poisonous gas containing arsenic [diethyl arsine, A s H ( C ~ H ~a) ~derivative , of the highly poisonous gas arsine, AsHal; but it is not at all probable that this gas was formed in the realgar mine mentioned by Strabo. I t is also of interest to know that Sinope had commercial relations with Greece; the realgar found at Corinth was perhaps imported from the mine in the mountains southwest of Sinope. The mineral was probably expensive. Realgar was produced artificially at an early date, and it appears to have been discovered by accident. Pliny says that Nikias (or Nicias) was the 6rst person to use the synthetic pigment. He was the artist who painted some of the marbles for Praxiteles. Shear reports that among the more notable discoveries made in the excavations of Corinth were several pieces of marble sculpture on which red paint was more or less preserved. He also has discovered specimens of a blue pigment in the theater district of Corinth. These specimens were examined by the writer, and reacted to the tests for Egyptian or Vestorian blue. This pigment was produced synthetically and used in Egypt for over two thousand years; it disappeared from the artist's palette somewhere between the second and the seventh century. As stated before, Egyptian blue is a richly colored glaze or frit. Vitruvius says it was prepared by beating together sand, soda, and copper, and that it was originally prepared in Alexandria. In his day (the time of Angustus) he said it was mannfactured in Puteoli. According to Professor Laurie. Principal of Heriot-Watt College, Edinburgh, analysis of samples of Egyptian blne shows that it usually contains lime, alumina, silica, soda, and copper. He says it can be produced by heating a mixture of sand, copper carbonate, soda, and lime to a temperature between 850" C. and 900°C. for several days. The specimens of the pigment examined at Princeton were found to be very insoluble, being virtually nnattacked by the powerful solvent, aqua regia. One formula assigned to Egyptian blue is CuCaSiOlo, a silicate of copper and calcium. I also examined a speci-
men of a bluish green pigment, discovered by Professor Shear a t Corinth, which proved to be a mixture of silica and of a compound similar to Egyptian blue. Professor Laurie says that if the temperature is raised too high in the preparation of the blue pigment, the green is obtained which was used so much in Egyptian painting.
Egyptians and Chinese prepared and used inks. Sir Flinders Petrie discovered a papyrus bearing written characters as old as 2500 B.C. It appears that ink was invented in China earlier than 2500 B.C. These inks were prepared from carbon (soot or charcoal) mixed with gum arabic, glue, or varnish. The Romans used as ink, sepia, which is a black pigment secreted by the cuttle-fish. INCENSE AND RESINS Iron-gall inks were prepared a t an early date. TheA Greek sarcophagus was uncovered in 1928 north ophilus, a monk of the eleventh century A.D., was perof the area of the Corinthian theater, and there was found inside the tightly closed co5n a light mass soine- haps the first writer to describe the preparation of what resembling bark or old wood; i t possessed a faintly nut-gall inks. Pliny, however, in the first century aromatic odor. Chemical tests showed that the ma- A.D. knew that paper treated with ferrous sulfate terial was rich in resinous matter; when burnt, it (green vitriol) could be blackened by immersion in an yielded a small amount of white ash. These tests indi- infusion of nut-galls. These inks were prepared by cated that the matter was of vegetable origin. This treating extracts of galls, bark, etc., with ferrous sulfate, conclusion was confirmed by a microscopic examination, ferrous tannate and ferrous gallate being formed. which clearly showed the presence of resinous sub- These compounds lack color, but when exposed to the stances and also revealed the cellular structure of vege- air they are oxidized to ferric compounds, which are table tissue or wood. The character of the material black. In the manufacture of nut-gall inks, a dye examined suggests that it came from an incense tree, is now added to make the ink visible when first applied. which may have been brought from the East. Chemistry has been most helpful in the restoration Frankincense (franc, free, pure encens, incense) of certain faded manuscripts. To illustrate, in the is a fragrant gum resin obtained from various East spring of 1928 the late Dr. Charles C. Marden, proIndian trees. It was used by the Egyptians, the Jews, and other ancient peoples for embalming, in connection fessor of Spanish in Princeton University, made a special trip to Spain to search for the missing portions of a with funeral rites, for fumigation, etc. manuscript upon which are inscribed writings by In Second Chronicles, 14:14, we find: Gonzalo de Berceo, a famous thirteenth century Spanish And Asa slept with his fathers, and died in the one and fortieth poet. The manuscript is parchment, and dates from year of his reign. before And they buried him in his own sepulchres, which he had made the first half of the fourteenth century-long for himself in the city of David. and laid him in the bed which America was discovered. After a systematic search, was filled with sweetodours and divers kinds of s~ices . .~ r .e ~ a r e dProfessor Marden was fortunate enough to find the by the apothecaries' art: and they made a very great burning missing parts of the manuscript and was permitted to for him. bring them to Princeton for translation. Being unable Frankincense was the most common incense offered to read certain portions of the manuscript, due to the to the Greek gods. We are told that Antigonus bad fading of the ink, be requested the writer to treat the a branch of the true frankincense tree sent to him; faded parts with a chemical reagent with a view t o also, that a branch of an incense tree was carried by their restoration. Proceeding upon the hypothesis that an ambassador from Arabia to Rome, in the days of a nut-gall ink was used by the transcriber, a dilute soluPliny. Sweet-smelling gums and resins of the countries tion of ammonium sulfidewas applied to the manuscript of the Indian Ocean were imported by Greece after the by means of a small sponge, with the hope that the Mediterranean trade with the East was opened up by faded iron compound would be transformed into sulfide the Egyptian king, Psammetichus (about 664-610 of iron, which is black. The result was highly satisB.C.). factory; indeed, we were able to photograph the reRiKS AND MANUSCRIPTS stored manuscript, and i t was quite legible. The chemist also has been of service in the study of I have recently removed ink stains from an old oil manuscripts and inks. It is known that the ancient painting by means of oxalic acid dissolved in alcohol.
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