tusks tusk pulp elephant dentine teeth found tooth purposes organic
IVORY is essentially equivalent to dentine, that hard substance, not wholly unlike bone, of which most teeth principally consist. By usage, however, its application has become almost restricted to the dentine of those teeth which are large enough to be available for industrial purposes, viz., the tusks of the elephant, the hippopotamus, the walrus, tire narwhal, and the sperm whales.
Ivory consists of an organic matrix or basis substance (which by prolonged boiling is converted into gelatin), permeated by an immense number of exceedingly fine canals. The matrix is richly impregnated with calcareous salts, which are probably held in some loose form of chemical combination with it, and is of such consistence that it retains its form after removal of the salts by an acid solvent. The canals start from the axial pulp cavity, and run in a direction generally outwards towards the periphery of the tusk ; in the elephant they are of exceptional fineness, being only about TA-u of an inch in diameter, and are placed very closely, being separated by intervals not much greater than their own diameter. To the regularity with which the tubes are disposed, and to their small size and frequent curvature, ivory owes its fineness of grain, and probably also its almost perfect elasticity ; whilst to the peculiarities of their curvatures it owes that very characteristic pattern of curved decussating linos, like engine turning, which is seen where the surface is a section transverse to the tusk. For, though it is broadly true that the tubes in elephant ivory run from the axis of the tusk to its periphery, they do not run straight, but make a succession of strong bends at regular intervals, and as the light is differently refracted by the basis substance and by the tubes according to the direction they are pursuing, this peculiarity of their course results in producing that pattern found in the dentine of Proboscidea only. Ivory differs from bone in its finer structure and greater elasticity, and in the absence of those larger canals which convey blood-vessels through the substance of bone, and appear upon it as specks or as stripes, according as it is cut transversely or longitudinally. When a transverse section of a tusk cut at a distance from the growing pulp is examined, its middle is seen to be occupied by a darkish spot of obviously different structure ; this is the last remains of the pulp, rudely calcified. The outer border of the section consists of a thick layer of cementum, with which the whole tusk is coated, and the rest is ivory, showing the characteristic engine-turning pattern, and, in addition to this, numerous circular lines, concentric with the central spot. These " contour " lines are due to the occurrence of a large number of minute irregular spaces, found in all dentine, but specially abundant and disposed with a greater regularity in ivory ; they are known as interglobular spaces, from the form of their boundaries when seen under a moderate magnifying power. In the areas occupied by these spaces there is a smaller proportion of lime salts and more organic matter ; consequently the ivory is here less dense and more liable to decomposition, and fossil tusks, as well as the less perfectly preserved of mammoth tusks, are frequently found to have broken up into a number of superposed cones, and in transverse section to present many concentric detached rings of ivory more or less friable. See Plate VII.
Arguing from the analogy of other dentine, it cannot be doubted that the minute tubes and the iuterglobular spaces are not empty in living ivory, but that they contain protoplasmic substance, though how far this may have perished or altered in that portion of the tusk which is extruded and far distant from the growing pulp can only be determined by observations at present wanting. According to Von Bibra's analyses, ivory contains as much as from 40 to 43 per cent. of organic matter, whereas human dentine contains only about 25 per cent. ; of fat it contains from •24 to .34 per cent. It differs from other dentines chiefly in its richness in organic constituents, in the fineness of its tubes, in their peculiarly curved course, and in the abundance of interglobular spaces arranged in " contour " The tusks of the elephant are a pair of upper incisor teeth, which may attain to an enormous development.. The largest teeth were possessed by the extinct mammoths, of which tusks have been found in Siberia 12 feet and more in length, and weighing 200 lb each. Holzapffel mentions one of very fine quality, that was cut up into piano keys in England, which weighed 186 lb. Among recent elephants the African species possess the largest tusks, these attaining to a length of 9 or 10 feet and a weight of 160 lb each, whilst the tusk of an Indian elephant which measured 8 feet in length and weighed 90 lb has been placed on record as exceptionally large. A pair of African tusks at the London exhibition of 1851 weighed 325 lb, and measured S feet 6 inches in length and 22 inches in circumference ; but authorities acquainted with the African ivory districts give 20 to 50 lb as the average weight of tusks. In Africa both males and females are furnished with large tusks ; but in the Indian species a sexual difference exists, the tusks of the female projecting only a few inches from the gums, while even of the males by no means all are " tuskers." Sanderson says that 10 per cent. of Indian male elephants have very small tusks, while in Ceylon only one in three hundred of the males is powerfully armed. The peculiarity is not always transmitted, tuskless sires (" mucknas") breeding " tuskers," and vice versa. The importance of tusks as giving an advantage in combat to their possessors is sufficiently indicated by the dread of a " tusker" shown by other elephants less favoured. Tusks are often broken by fighting, and always show marks of considerable wear, while even captive elephants, with their shortened tusks, make great use of them for a variety of purposes ; for example, an elephant will, when set to pull at a rope, take it between his molar teeth and pass it over one of his tusks to get a good purchase. Nothing but an extremely strong and elastic material such as ivory is could withstand the strains to which it is constantly exposed.
Captive elephants have their tusks shortened, and the ends bound with metal to prevent their splitting ; and, as the tusk is continually growing by the conversion of fresh portions of vascular pulp into ivory, the operation has to be repeated. When this is done at intervals of ten years, the segment cut off is valuable, and is sold as ivory ; some prefer, however, to cut the tusks much more frequently. In a young elephant the vascular pulp extends beyond the portion of the tusk implanted in the jaw, while in the older animal it does not reach so far ; its probable extent has to be borne in mind in shortening the tusk, as if it be encroached upon much suffering is entailed on the animal. Yet the vascular formative pulp of an elephant's tooth is singularly tolerant of injury without having its function of ivory formation destroyed, and hence it happens that foreign bodies which have got access into the pulp chamb4i.r become solidly enclosed in ivory. The growing end of the tusk is widely open, and its edges are not much thicker than paper ; the cavity which contains the pulp is of conical form, tapering to a point, which is situated at a distance clown the tusk, varying, as has been before stated, with the age of the animal. The tusk grows by the conversion of successive portions of the surface of the conical mass of pulp into ivory, whilst fresh pulp is added at the flat base or open end of the tusk. The tusks are deeply implanted in curved bony sockets, which run nearly vertically upwards, so that the open growing ends of the tusks are brought up to about the level of the eyes. Hence it is not a rare occurrence for a sportsman's bullet, intended to pierce the elephant's brain, to penetrate the tusk near to its growing end, where the walls of the pulp cavity are quite thin, and to lodge in the " nerve " of its tooth. Indeed sportsmen remark that the forehead shot i3 less fatal to African than to Asiatic elephants, owing to the size and position of their tusks. The amount of disturbance produced by a bullet in the nerve is variable; sometimes the conversion of pulp into ivory goes on with but little interruption, so that the bullet comes to be imbedded in ivory, which fits closely up against it, instead of in pulp as it was at first. Generally the pulp immediately around it has been so disintegrated by its impact, or by subsequent inflammation, that it is incapable of conversion into normal ivory, and in its place there is a more or less irregular development of nodular secondary dentine. And sometimes there is a failure to produce even this less highly organized tissue in the immediate proximity of the bullet, which then ultimately comes to lie loose in an irregular cavity completely surrounded by secondary dentine. Of a similar nature is the so-called " abscess in ivory "; this was really an abscess in the formative pulp surrounded by a limiting membrane ; as the conversion of the pulp into ivory went on, calcification passed all round the abscess and enclosed this, pus, membrane, and all, in solid ivory ; and there it is discovered by the ivory cutter as an empty hole lined by a thin dried skin, the old abscess sac.
African natives sometimes spear elephants to death when they have been surrounded by an extemporized barrier of twisted creepers, and for this purpose some of them climb into trees ; they also set traps made of a very heavy piece of wood shod with an iron spearhead, arranged to fall upon the elephant as he passes along a track beneath (Du Chaillu); elsewhere lances of extreme length are used in the same way. The open base of the tooth, containing the formative pulp, looking directly upwards, a spear from above intended to fall upon the head or to " pith " the animal might easily enter it, and break away, leaving the point in the tooth pulp. In a specimen now in the museum of the Odontological Society, London, such a spear head remained without stopping the further growth of the tusk, and came to he solidly enclosed in ivory and secondary dentine, although it measures no less than 7,1, by LI inches. Not a trace of its presence was discernible upon the exterior of the tusk, and it was only discovered when the tooth was sawn up. This specimen is not unique, there being said to be another, which has been turned into a cup with the imbedded spear head as its stem ; and there is a specimen of a javelin head firmly built in by ivory in the museum of the Royal College of Surgeons. But that au elephant is not wholly indifferent to a large foreign body in the nerve of his tooth is proved by the fact that a notoriously fierce and dangerous " rogue " elephant in Ceylon was found when killed to have been suffering from inflammation and suppuration consequent upon the presence of a bullet in the pulp of a tooth ; the supposed madness of the famed elephant of Exeter Change was also found to have been due to the pain of a diseased tooth. A common result of injury to a growing tusk is the conversion of a portion of the pulp into irregular globular masses of secondary dentine, - sometimes enclosed solidly in the midst of normal ivory, sometimes forming loose masses as big as lien eggs in the pulp cavity, and sometimes stalagmite-like appendages to its walls. Of course such deviations from normal structure seriously injure its value for industrial purposes, and they are specially apt to occur in domesticated animals whose tusks are being repeatedly shortened, the cut not being invariably made at a sufficient distance from the apex of the living pulp. But under no circumstances is the ivory from domesticated elephants so highly esteemed as that from the wild animal.
The large balls of secondary dentine appear on section as a conglomerate of spherical 'masses bound together by softer and looser-textured materials ; they are sometimes beautiful, but cannot be made much use of. Small spots of globular dentine sometimes occur in the midst of normal ivory, for which no cause can be detected. Malformed tusks are far from rare ; the College of Surgeons possesses one about 2 feet in length, the base of which is an irregular mass of osteodentine nearly as large as a man's head. Spiral tusks are also met with, and are almost always the result of some disease of one side of the pulp, leading to a slower growth on the one side than on the other. Much of the ivory of such tusks will be faulty ; they should not be purchased except as curiosities.
The best ivory is the African, and the first quality of that comes from near the equator ; much is brought down by natives by land from the interior, whilst in other districts expeditions are organized by Europeans to go into . the interior, and collect the stores gathered by native-tribes ; 20,0001k, valued at Khartoum at ..E4000, would be considered a good result for a season's expedition with one hundred and fifty men. The price of ivory varies much in different districts, being generally higher on the west than on the east coast ; the transaction is generally one of barter, and the price therefore difficult to estimate. The tusks are sold by weight, and stones and iron are sometimes thrust down into the hollow pulp cavity to increase the weight, so that dealers generally feel down the hollow with an iron rod to detect foreign matter. The value of the ivory depends upon the size of the tusks ; those below 6 or 7 lb weight are not worth more than half the price per lb of really fine tusks. Something depends on the care bestowed upon the tusks, which are sometimes roughly treated, while others are waxed and- carefully wrapped up for protection. The African ivory trade is an ancient one, and in medieval times Marco Polo speaks of the traffic in ivory at Zanzibar as being astonishing in its amount.
The tusks of the mammoth from northern Siberia are said to furnish almost the whole of the ivory used by Russian ivory workers. They are found in most extraordinary abundance, and it is said that from the time of Dr Breyne's quaint paper " Behemoth " in the Philosophical Transactions for 1737 till now there has been no intermission in the supply. They come principally from the neighbourhood of the Lena and other great rivers discharging themselves into the Arctic Ocean, and are abundantly found in the Liakhoff Islands. Mammoth tusks are slenderer, much more curved, and in proportion to the size of the animal much larger than those of recent elephants. In Siberia at different times four mammoths have been found entire, their hair, skin, and even all their soft parts having been preserved without change in the ice for countless years. Just as in some few cases all the most perishable soft parts were preserved, so in a vastly greater number the less perishable ivory was kept without change by the low temperature and exclusion of air ; thus when in the summer the ice tears down portions of river banks, or floods break up frozen morasses, the tusks are brought to light. Some are in the most beautiful preservation, like recent ivory ; others having been exposed before, in previous summers, their organic constituents have partly perished, and they are inclined to become broken up along the lines of interglobular space into concentric rings, or may have become so disintegrated that a fragment may be used like chalk to write with.
In England this ivory is not very highly esteemed, being considered too dry and brittle for elaborate work, and to be very liable to turn yellow. Most ivory workers strenuously deny ever using them, but, though more rarely theta in former years, mammoth tusks are occasionally imported. Within the last few years an exceptionally large tusk in splendid condition was offered for sale to the Oxford University Museum at a price of £100, but was not purchased. In 1872 1630 very fine tusks were brought to England ; and in 1873 1140 tusks weighing from 140 to 160 Ib each were imported. The best were sold at a very good price, but proved less available, even for such purposes as cutting into knife handles, than was expected, and although smaller importations arrive from time to time they can hardly be considered as a regular article of commerce, and are difficult of sale ; some have been very recently sold at a price so low as ten shillings a cwt. Westendarp personally investigated the Siberian ivory trading districts, and returned with no favourable impression. He found that about 14 per cent. of the teeth were good, 17 per cent. could be made some use of, 54 were quite bad, and 15 wholly useless. The ivory looks better outside than it really is, and, as only about 30 per cent. is usable, it does not pay well for transport. He thought it not worth more than ls. 6d. a pound.
The finest quality of ivory from equatorial Africa is closer in the grain, and has less tendency to become yellow by exposure than Indian ivory. When first cut it is semi-transparent and of a warm colour ; in this state it is called " green " ivory, and as it dries it becomes much lighter in colour and more opaque. This is supposed to be the result of the drying out of the " oil " ; but ivory contains less than one-half per cent. of fatty material, and that which dries out is water, not oil. During this drying process the ivory shrinks considerably, so that it is necessary to season it like wood when such things as box lids, which need to fit, are to be made from it. The tusks shrink much more in their width than in their length, which will be readily understood when the many concentric rings of interglobular spaces, containing soft material, which dries up and leaves them empty, are remembered. It is on account of this peculiarity of structure that billiard balls are turned from tusks not greatly exceeding them in diameter, for by the selection of such tusks the ivory on the opposite sides of the ball will correspond in density and in structure, and the shrinkage will be uniform about its centre. They are usually turned roughly into shape, kept for some time in a warm room to shrink, and then turned true. The thin plates cut for piano keys are dried and shrunk at once by being baked for a time in an oven, but after being dried they are still subject to changes in bulk in a moist atmosphere.
It is not always possible to judge of the quality of ivory before the tusk is cut• up. The exterior, or cementum, should be smooth and polished ; it is often of a deep coffee colour in the best tusks, and it should not show any large cracks. But the most profound disorganization of the ivory may exist inside an exterior which promises well, or it may be badly cracked from unequal shrinkage in drying without cracks being noticeable on its exterior. About half of the length of an average sized tusk is implanted ; this will be hollow, and in a young animal the hollow will extend beyond the implanted portion ; the extruded part, recognizable by the deeper colour of its cementum, is solid, and is circular or oval in section. Great care is taken by ivory cutters to cut up the tusk to the greatest advantage, its high price necessitating the strictest economy in its use. Veneers of large size have been cut by a reciprocating saw cutting a spiral shaving round the tusk, one having been thus produced 40 feet in length by 12 inches in width ; but they are not of much practical value, save as an example of what is possible. With age ivory turns yellow, and various receipts are given for restoring its whiteness ; but they mainly depend upon mere removal of the outer surface, and no satisfactory method of bleaching it is known ; it preserves its colour best when exposed to light. Considering the high percentage of organic matter which it contains, it is surprisingly durable. In some of the ivories brought by Mr Bayard from Nineveh, in which the organic constituent had partially perished, leaving them very friable, its place was supplied by boiling them in a solution of gelatin, a process suggested by Professor Owen as the likeliest means of restoring to them something like what they had lost during the lapse of time by exposure. It is possible that by some such treatment the perished ivory of the mammoth may be rendered useful for some purposes. The existence of chryselephantine statues of Phidias, and of flat plaques of ivory larger than could be cut from any known tusk, renders it probable that ancient workers possessed some method of bending it; and receipts have come down from the 12th century for softening it so as to alter its form. But these, which depend upon its partial decalcification, have not been found to yield the excellent results claimed for them, and the larger plaques in question present no appearance of having been submitted to any such process. Moreover, Westendarp states that from a tusk weighing 200 le the largest plaques he knows of could have been cut. Ivory can be made flexible by submitting it to the solvent action of phosphoric acid ; when washed and dried it becomes hard, and when moistened again it resumes its flexibility ; but this is at the sacrifice of many of its properties.
Ivory takes a variety of dyes well, without interfering with the polish of its surface ; the actual matrix is stained, and the colour is not merely due to the penetration of pigment into the open dentinal tubes.
The great canine teeth of the hippopotamus furnish an ivory which is harder and whiter than that of the elephant, and less prone to turn yellow ; these differences are probably due to its containing a smaller percentage of organic matter. It also lacks the engine-turning pattern of elephant ivory. The tusk of the hippopotamus is a tooth of persistent growth, strongly curved into a segment of a circle, and solid in the greater part of its length. It is thickly coated with enamel on its exterior surface, and is triliedral. On transverse section the remains of the pulp cavity are seen as a line or fissure in the middle, aril occasionally there is a nodule of secondary dentine in it. The ivory is not quite homogeneous ; for the back of the tooth, which is not covered with enamel and in use wears down the fastest so as to keep a sharp edge to the tusk, is markedly softer than the rest of the tooth. No large piece can be obtained from a hippopotamus tusk, and the incisors ant the upper canines yield even smaller pieces than the lower canines. Thirty years ago there was a considerable demand for them for dentists' use, and at that time a fine tusk of 5 lb weight was worth from five to seven guineas, but the price is now much lower, and comparatively few are imported.
Amongst the northern nations the tusks of the walrus have long been used as a source of ivory. The great upper canines consist of a body of dentine invested with cementum ; they are oval in section, solid, and their axis is made up of secondary dentine, which is far larger in amount than in the hippopotamus, and makes up a considerable part of the whole tooth. This is very nodular in appearance when cut and polished, but is of dense and tolerably uniform consistence.
The spirally twisted tusk of the narwhal, the teeth of the sperm whales, the ear bones of whales, and the molar teeth of the elephant, are also all made use of as sources of ivory, though they are far less valuable than the larger tusks. For the subject of carvings in ivory, see CARVING, VOL V. p. 167. The earliest piece of ivory work known is a rude incised drawing of a mammoth upon a fragment of mammoth tusk, which must have been executed by a contemporary of the animal. Numerous references to ivory occur in the Old Testament, which show that it was regarded as of great value. It seems to have been used for the decoration of the temple, and it is often mentioned amongst the presents brought to kings, who employed it for purposes of regal state. Some, however, of the references would seem more strictly applicable to wood than to ivory.
The Nineveh ivories in the British Museum are of very great antiquity, a probable date of 900 B.C. having been assigned to them ; yet many of them are in good preservation, and others have been tolerably well , restored by boiling in gelatin. All exhibit considerable artistic merit and mastery over the material, whilst some reach a very high degree of excellence alike in design and execution. Competent judges declare that, underlying the obviously Egyptian character of the work, there are differences sufficient to lead to the inference that the ivories were not executed in that country. Some of them consist of thin plaques on which figures were delineated by means of incised lines ; some were carved in low, and others in high relief ; whilst there are many examples of detached heads, and even entire figures, carved in close imitation of nature (see Plate VII.). Traces of gilding remain on many of them, and they were of ten further enriched by being inlaid with fragments of lapis lazuli, or of a coloured glass in apparent imitation of this ; the eyes of the larger heads were generally rendered conspicuous by this means. In one of the panels figured, the border of the dresses, the thrones on which the figures are seated, the ornaments above the cartouche, and the symbols upon the cartouche itself were thus inlaid with colour. The largest object is a carved staff, perhaps a sceptre ; amongst the smaller pieces are heads of animals and entire animals, griffins, human heads, crossed and clasped hands, rings, th. Like the ivory carvers of later times, these early workers seem to have studied economy of their material ; thus a beautiful carving in high relief of two griffins standing upon papyrus flowers has been carved on the interior of a segment of a large tusk, the natural curvature of which it follows. The tendency of ivory to decompose into concentric layers parallel with its exterior has been already noticed, and Mr Bayard himself speaks of the trouble he experienced owing to the flaking of the pieces lie discovered ; it is by the separation along the contour lines that many ancient ivories have been spoiled. Besides those discovered at Nineveh, some other ivories of great antiquity exist ; and ivory workers are mentioned as a distinct class of artificers at the commencement of the Christian era. Many writing tablets of ivory, with raised rims inside, where wax was spread over their surface, have come down to us ; these were (Iften made to fold together, and the exterior richly ornamented with carvings. It was the custom for newly appointed consuls under the empire to send these plaques to persons of importance, and the covers sometimes have upon them representations of the consul in his robes of office.
One of the most beautiful of ancient ivories is the Roman 3d century plaque purchased by the South Kensington Museum for £400 (see Plate VII.). It forms one half of a diptych, and measures 114 by q inches. The other half is in the Hotel Cluny.
From these times down to the present day there has been a constant succession of ivory workers, though in medimval times artists of higher ability were to be found than any who will now devote themselves to such work. A large proportion of the carvings deal with sacred subjects : one of the most beautiful is a Pieta, the virgin holding the dead body of Christ in her lap (see Plate VII.); this was executed about the 14t11 century. Illustrations of old romances were frequently made use of to decorate mirror cases, boxes, &c., and elaborately carved chessmen of walrus ivory referable to an ancient period have been found in the island of Lewis. Schliemann, in his excavation at the supposed site of Troy, found many useful articles made of ivory, - pins, buckles, &c., - but no carvings, even of rude character.
Among the chryselephantine statues of ancient Greece executed by Phidias, Praxiteles, and others, one of Minerva in the Parthenon was 40 feet in height, and was con: strutted of ivory and gold ; others are mentioned as made of wood, with face, hands, and feet of ivory. Yet in some cases it is expressly said that the statue was entirely of ivory, special exception being made of a portion of the dress which was not. Among the Nineveh ivories are some which apparently belonged to figures partly wood and partly ivory, but these were of no great size ; the wood employed seems to have been ebony.
In former times ivory was frequently used for the manufacture of artificial teeth ; but this has become a thing of the past, ivory having been superseded by more durable and more manageable materials. Its use for this purpose is quite ancient ; thus Martial contemptuously speaks of a lady of his own time " emptis ossibus indicoque cornu" as having but a poor chance of passing them off as her own teeth. For the use of the dentist elephant ivory was less suitable than that of the hippopotamus or the walrus ; of these two the former was generally preferred. The enamel was chipped off with a chisel, or made to fly off by a judicious application of a blowpipe flame, and the tusk was so cut that the plate might consist as far as possible of the hardest part of the dentine which had formed the front of the tooth. This, carved up to fit the mouth accurately, formed a supporting plate which commonly carried in the front actual human teeth secured by pins, though sometimes the teeth were formed of ivory carved in imitation of teeth, and at the back blocks of hippopotamus or walrus ivory were added for the purposes of mastication, They were called "bone pieces," though there was really no bone used in their construction; their durability was in no case great, though it varied in the mouths of different persons, and a plate had to be ultimately discarded on account of the ivory getting discoloured, softened, and offensive. For dental purposes walrus ivory was more durable than hippopotamus, but its colour was not so suitable, nor was it so hard. Some specimens of native Indian dental work in ivory exist, but these have probably been copied from plates worn by Europeans.
The principal demand for ivory, beyond the purposes already alluded to, arises in connexion with the cutlery trade, very large quantities being used for the handles of pocket and table knives. It is also extensively employed for the handles of walking sticks and umbrellas, for combs, paper knives, and ladies' fans, and for measuring rules and mathematical scales. Further, it is in considerable demand for the manufacture of chess and draughts men, for statuettes, rilievo plaques, caskets, and many minor objects of furniture, decoration, and ornament, and for the purposes of inlaying. Dieppe is now a principal centre of the European ivory manufacture.
But it is in the East, and especially in China, that ivory is now most highly prized and most elaborately worked into decorative forms. No amount of patience and care appears to be considered excessive among the Chinese for the decorative working of ivory, as is obvious in the extremely minute and delicate workmanship in their lace-like carved open-work trays, while their carved nests of concentric ivory balls are still reckoned among the puzzles of industry. By the Japanese ivory is equally held in esteem, and is decoratively treated in their peculiar mainfer in the form of spill cases, medicine boxes, and the elaborately carved and ornamented nitsuke or large buttons. In India ivory is extensively used in the inlaid work of Bombay, &c., and for furniture decoration generally ; and it is also cut into long slender filaments for making the tails of state chowries or fly-flappers, which, both handle and tail, are in many instances made of ivory.
All ivory dust, chips, and pieces unsuited for working are utilized by -being converted into gelatin, which they may be made to yield by prolonged boiling, or by being calcined into ivory black. Confectioners are said to make use of ivory dust as a basis for soups, and it forms an excellent colourless size, employed for delicate purposes. When ivory is calcined in a close chamber, in which there is not enough oxygen to burn the carbon into carbonic acid, the organic matrix is burnt into carbon with which remain in the most intimate admixture the lime and magnesium salts which had previously hardened it. Strange to say, the calcined ivory retains its form and texture notwithstanding the destruction of the organic matrix, and specimens sometimes show the engine-turning markings on the cut surface with the utmost distinctness. It is an animal charcoal of great purity, and owes its delicacy and particular properties to the extremely fine division of the carbon particles. When ground up and mixed with appropriate media, it affords both to the oil and the watercolour painter a most valuable black pigment ; it is also used as an ingredient in the fine printing ink used for engravings anZetchings.
- Attempts have been made to manufacture an artificial ivory, but with no very satisfactory result. Billiard balls and other small objects have been manufactured of celluloid, a combination of gun cotton and camphor with ivory dust, which becomes plastic at a temperature of about 2S0°, and when cold is again quite bard and somewhat translucent. Plaster copies or reproductions of artistic ivories are prepared, under the name of fictile ivories, by casting in very fine plaster of Paris tinted with yellow ochre, and subsequently treating the surface with a mixture of wax and spermaceti or stearine. But it may fairly be said that for the purposes to which ivory is ordinarily applied no substitute approaches it either in beauty or in those other qualities which render it so agreeable and so satisfactory a material for the workman, whether carver, turner, or miniature painter.
Sec Dr Breyne, Phil. Trans., 1737 • Owen, On the Ivory and Teeth of Commerce," in JOUrn. ,Soc. of Arts, 1856 ; Principles of Geology ; Boyd Dawkins, Casscll's .Natural history, vol. ii. ; C. S. Tomos, Dental Anatomy ; Catalogue of annterian Museum, Royal College of Surgeons ; Holzaptfel, TU171'1779' and _Mechanical Manipulation ; South Kensington _Handbooks, "Ivories"; Colonel Yule's Afare0 Polo ; Du Chaffin, Equatorial Africa; Burton, First Footsteps its Eastern Africa; 'ferment, Island of Ceylon ; Bowling, Kingdom of Siam ; Westezlarp, ll7itlhsit. der geogr«ph. Gesellschaft, Hamburg, 1878-9 ; Layard's aYineveh and its Remains; Snhliemann's Rios. (C. S. T.)