W^'-^W^^'^':-^ ,^-,,«.5 ■;*;■' .-. ■ • ■.;. ■ [ ;■ THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES ccriL' ON THE STRENGTH AND BEAUTY OP MINER xlL TEETH. BY EDAVIN \ TKUMAN, M.R.C.S., U-^ L»K.Niiol IN OKDINARY TO HER MAJESTY'S HOUSEHOLD J FELLOW OF THE ROYAL MEDICAL AND CHIRUKGICAL SOCIETY ; AND HON. FELLOW OP THE CENTRAL SOCIETY OF DENTISTS OF GEiftlANY. A Paper Read before the Odontological Society, May 4, 1862. (J^or ^Iribatc dknilation. MDCCCLXII. WOv^' ON THE STRENGTH AND BEAUTY OP MINERAL TEETH. ON THE STRENGTH AND BEAUTY MINERAL TEETH. BY EDWIN TEUMAN, M.RC.S., DENTIST IN ORDINARY TO HER MAJESTY'S HOUSEHOLD ; FELLOW OF THE ROYAL MEDICAL AND CHIRUKGICAL SOCIETY ; AND HON. FELLOW OF THE CENTRAL SOCIETY OF DENTISTS OP GERMANY. A Paper Read before the Odontological Society, May 4, 1862. ((for iprHralt Cmttlslion.) MDCCCLXII. T77k ON THE STRENGTH AND BEAUTY OF MINERAL TEETH. Mr. President and Gentlemen, I am about to give you a rambling history of my search, mental and physical, for the principles on which depend the strength and beauty of mineral teeth. I choose this arrangement, firstly, because it will render my subject more interesting to our younger members ; and, secondly, that I may, as I proceed, acknowledge the sources from whence my knowledge is derived. The universal use of porcelain as a material of which to construct artificial teeth renders a know- ledge of its manufacture, chemical combination, and properties under various influences essential to the Dentist. All materials used in the arts have to be viewed in three aspects. — 1st. Their source, consti- tuents, and combinations. 2nd. The treatment they will be subjected to in the processes of manufacture ; and 3rd, the properties required in the product. A 4 ON THE STRENGTH AND BEAUTY In the manufacture of porcelain, all tkree of these views present great diversity, and require separate and especial study, 1st. The constituents of this substance are numerous, and vary much in quality. 2nd. The treatment of this substance is even of more consequence than its composition, as from the same constituents, combined in the same quantities and with equal care, a difiference of treatment will produce two entirely diflferent results. 3rd. Porcelain is required to possess varying pro- perties suitable to the very various purposes to which it is applied. For Dental purposes alone many kinds of porcelain are required ; and as, then no one form of porcelain is endowed with aU the properties we want, many kinds of that substance are required for our purposes ; and, therefore, it is essential that this substance should be thoroughly investigated. In most manufactories the secrets of the art are jealously guarded by the manufacturer, but in none mth the same rigidity and persistence as in those of earthenware, a circumstance that renders the intro- duction of porcelain for new purposes doubly difficult, it being almost impossible for the student to master the rudiments. Until lately, in the few books written on the subject, scarcely anything beyond the history of the art and its early processes is given. So secretly indeed has this branch of art been followed, that even Wedgwood has not left OF MINERAL TEETH. 5 behind him a line to guide us to reproduce Hs bodies and effects. During the last few years a few good and useful books have appeared, but even now every novice is left to discover anew for himself much that is well-known and hidden by those around him, and this arises in a great measure from practice being far in advance of theory, for experienced workmen produce many effects which chemistry cannot account for. With these facts before me in 1851, I com- menced my search after what I may call the philo- sopher's stone, or rather as poor Palissy would have said, the white enamel ; but in my case a body that should possess the requisite properties for artificial teeth, viz., strength and the power to resist alteration of temperature, with that creamy-like appearance which natural teeth so eminently possess, and which was not then to be found in porcelain generally. I sought first, among the mineral teeth already in use, the absolute state of things then existent. I examined the teeth of the various manufacturers : some were very transparent and deficient in strength, others were stronger, but too opaque, and moreover defective in shape ; in fact, to my mind, there was not one tooth combining all the requisites, and none were of natural appearance ; they would pass in the mouth for teeth, but as products of art, they were by strict criticism defective. In looking to books for help, I found a few American works on the subject, and one or two small 6 ON THE STRENGTH AND BEAUTY papers emanating from English Dentists, but the latter merely gave simple formulas, some of which were incomprehensible from the omission of neces- sary information, while many were impracticable ; here are two formulae from the same page of an English work : 1 st Feldspar 1 8 Disintegrated, 6 Kaolin, 2 Silex, 1 2 2nd „ 36 „ 3 „ 2 If one is right the other must be wrong. Which is best ? In some of these works materials were mentioned of which we have no samples in England except in museums, and concerning which no guidance was given to enable us to discriminate in their selection. To apply to manufacturers was useless. What, then, was to be done, but to commence the study of porcelain, and, by dint of perseverance and labour, work it out experimentally 1 In describing the measure of my success, it will not be necessary to weary the meeting with all the dry details and analyses through which I waded, or mention all the thousand failures that saddened me. I have bright sunny days of hope, and kindnesses received from many to recount, that fill me with joy as I look back on the last ten years spent in this research, which show how the lovers of high art will help forward the industry of the poor student, and not lock up every particle of knowledge that aatH produce a shilling. After becoming conversant with the general out- OF MINERAL TEETH. 7 line of porcelain manufacture from books, especially from * Knapp's Chemical Technology,' I found one of my workmen, Mr. Grinton, had done something in the making of mineral teeth in Edinburgh, and from him I received this formula — Feldspar 1 oz. Pumice 2 sc. Crystal 10 gis. Rutile 1^ grSr We at once put the formula into operation as ,well as we could. Our moulds were plaster, taken from other teeth ; and for baking I built a furnace on what was thought to be a good principle. It was an ordinary enamel furnace wit;h a muffle, having a flat bottom, straight sides, and a round top. We used coke as a fuel, and placed test-pieces of the body, wliich were withdrawn at intervals through a door for examination. A product of this our first essay is on the table marked No. 1, and with the results of the experiment I was, on the whole well pleased, and determined at once to produce good moulds and some teeth for use, as it was evident, even at this early stage, that great practice would be required to make a good tooth. Moreover, a pyro- meter to measure accurately the heat became an im- perative necessity. I next arranged to visit the Pot- teries, and get a more practical knowledge than books could give. With this view the Staffordshire works, where admittance could be obtained, were visited, and much information in ordinary porcelain work- 8 ON THE STRENGTH AND BEAUTY ing was gained, especially from an old school-fellow Mr. Thompson, of Wood\ille ; but in none of the works inspected have teeth been made ; their bodies entirely differed from that required, and most of their operations were not at all applicable to our use. I next applied to one of the large houses to supply me with materials, and having told them my object, asked them to help me. The materials were sup- plied, I believe, to the best of their ability ; but no information was given, and the employes could not conscientiously impart to me the particulars of bodies or of causes. One gentleman gave me a bit of body, but would not teU me of what it was made, nor the method of treatment. That product is marked No. 2. I believe it to be a good body, I had some time before attended a course of lectures at the Museum of Practical Geology, by Dr. Percy, and I requested him to find me a practical chemical assistant, capable of aiding me in these investiga- tions. Dr. Percy introduced me to Mr. Dick, a gentleman of great ability and industry ; and here let me say, that the hours spent by me in his society, over our furnace, were very pleasantly passed. Mr. Dick suggested a series of experiments, to ascertain — first, in what the strength of mineral teeth them- selves consisted ; and second, if other minerals than those already tested would produce a better body for teeth, as cost would not be an impediment. The residts of our first proposition I shall give here- OF MINERAL TEETH. after. Our second I will dispose of at once. We commenced by taking feldspar alone as our fixed minimum, and that of a kind which we could pro- cure of uniform quality in any .quantity, and I may say that all my experience has tended to show the wisdom of this suggestion, both as regards the material itself, and also its uniformity ; for it is a substance so often mixed with other minerals, and especially with quartz, that before using it the particular specimen should be well tested, otherwise, as has often happened to me, all the future labour will be thrown away. I shall presently show what I recommend on this subject. Apatite was the first mineral that we tried ; and our plan was to take 100 grains of material for each test, altering the proportions by a gradual increase of the material added to the spar, and baking ten tests of each mixture, as thus — Feldspar. ,98 Apatite, 2 » 96 ,, 4 » 94 „ 6 » 92 „ 8 j> 90 „ 10 » 85 „ 15 j> 80 „20 » 70 „ 30 » 60 „40 «i 50 » 50 The mixtures were ground up together in dis- tilled water, excess of which was drained off on a porous tile ; some teeth were made out of each 10 ON THE STRENGTH AND BEAUTY mixture. Next feldspar, apatite, and fluor-spar ; then feldspar, apatite, and quartz ; afterwards beryl, pumice, magnesia, petalite, various clays, pure alumina and sQica, and many other substances, in every proportion, together and separately, and with all the varieties of feldspar we could procure, a strict account of the particulars first named, and of the results of all our bakings, being kept. The results were not very satisfactory, though the labour was great and at the time so little pleased were we, that JMr. Dick, who was called away to an important appointment in Spain, said he believed we left ofi" just where we began. That, however, was not the case, as I had gained the experience and advantage of his excellent method of investi- gation for my future guide. My workman also, Avith whom I first worked, left me at this time to go to America, and therefore, being again alone in my labour, I endeavoured to perfect my moulds, which I constructed of gutta-percha, taking natural teeth as fine and large as I could get them, that their extra size might allow for the shrinking of the material, and in some instances cutting them into halves, and inserting a slice of wood or ivory between the several portions, to iacrease the width ; sometimes, also, cutting the teeth across, and in- serting a plate in the interspace to increase the length of the enamel. Then I embedded the natural tooth not quite half way in a perfectly OF MINERAL TEETH. 11 smooth, flat surface of gutta-percha, putting four or six into one mould, the gutta-percha, being moulded in an iron frame, with a moveable bottom and top that exactly filled the inside of the ring or box, but would move up and down within it. I afterwards replaced the gutta-percha base, together with its embedded teeth, and on them put a given quantity of soft gutta-percha, and on that the moveable top, and submitted the whole to pressure in a very powerful press. The result was, of course, an elastic mould, with a three-quarter impression of the pattern tooth. Thus were gained some very essential points not hitherto attained — a most perfect mould of the enamel surface, every characteristic being accurately preserved, and also a perfect profile (a matter of the greatest consequence, as these teeth, when cut on the crown, always present a natural appearance), the elastic nature of the mould permitting the exit of the moulded tooth through an opening otherwise too small. On slightly bending the moulds backwards the teeth fall out on to a piece of wadding, quite perfect. These moulds I have always since used, and if made of good gutta-percha, properly prepared, and kept in water when out of use, are very durable, and after they are worn out, a very few minutes will reproduce them, as the same material will do again, and the matrix in which they were made remains uninjured. A great advantage in this plan 12 ON THE STRENGTH AND BEAUTY is, that the pattern teeth, if large, need not be injured at all, so that we can copy any fine teeth from specimens wre may have or borrow without detriment to the preparation from which they are taken. The moulds I have described apply to half teeth only. If a back is used for putting in the pins, it may be either metal or plaster. If the teeth are cast — a process which I hope to explain at a future time — of course plaster backs are the thing. If pressed, metal ; for tube teeth the matrix must be different, or the moulds altered after they are made ; for molars and bicuspids, or for vulcanite teeth, the moulds are made in several pieces, as shown on the table, and this, with gutta-percha, is very easy, as this substance will not adhere either to itself or to metal, if one of the surfaces is cold, and it can be planed like wood, so that a perfectly smooth, even, rectangular surface is readily procured. The moulds are a very important matter — in fact, after a good body, the most important in this manufac- ture — and if made in metal the cost is very great, consuming the largest amount of the capital employed, as they must necessarily be very numerous to produce the great variety of sizes and shapes required. They also take so long to make that any change in shape, or even alteration in size of the teeth, is a serious affair ; whereas by the proposed plan, every variety of tooth can be imitated, even for particular cases, with the greatest facility and at OF MINERAL TEETH. 13 little cost ; not that cheapness is very desirable — our primary object is to attain perfection ; and if a better method can be shown — one, that is, that would produce a nearer resemblance than this can to natural teeth — ^that method shoud be used regard- less of cost. It will be found that the cheapest road in the path of original investigation is so much the longest that few can afford to travel by it. The moulds being an accomplished fact, and the beauty of form being attained, a great many teeth were now made, using different bodies, always endeavouring to have two or three series of experi- ments simultaneously in progress, and never forget- ing the principles sought for, viz., strength, beauty, and endurance of vicissitudes of temperature in the product. The nearest known porcelain to this standard was the Berlin, as used for chemical pur- poses. Notwithstanding aU that has been said about trade secrets and the rigidity with which they are guarded in all the porcelain factories, I deter- mined to go to Berlin and ask the manufacturers for help, and, as the event proved, not wdthout an issue. To the deep interest felt by the late Prince Consort in the arts and manufactures of this country is due the success of my mission. The present King of Prussia, at the instance of the Prince, furnished me with an autograph letter to the Director of the Royal Porcelain Works at Berlin, requesting that my questions might be answerd — but I anticipate. 14 ON THE STRENGTH AND BEAUTY Having determined to take this long journey after my pet object, it appeared desirable, if possible, to take other Continental factories on my way, and for this and other reasons fortify myself, as far as pos- sible, before starting, with letters of introduction from my friends in England. I may here be allowed to mention that I owe the opportunity of obtaining the information made use of in the present paper principally to the kind- ness of Sir James Clark, who interested himself in the scientific question so far as to obtain for me the necessary introductions, and not the least valu- able of those was that to Professor Hofmann, who kindly gave me letters to Dr. Lowe, of Vienna, &c. With these credentials I started, passing through Holland on my way for the purpose of visiting Delft, the birthplace of pottery in Europe. I relate all these (perhaps irrelevant) particulars of the obligations under which I have been placed, as an acknowledgment of the debt of gratitude I have contracted, and which will be contracted by those who may find available information in the paper. The smallest particle of knowledge on the subject of porcelain manufacture is looked on as a treasure of great value, and justly, as a lifetime of labour may be saved by a momentary communication. Hence, how shall we sufficiently thank those unselfish ones who impart it to us 1 The pottery at Delft is a very small affair, quite OF MINEKAL TEETH. 15 behind the rest of Europe in its wares, which are as old-fashioned as the venerable town itself, and even truly venerable in their prejudices are they who make them, for not a toe could I put within their door, although armed with an introduction from a friend of the proprietor ; and, more strange still, to unlock the door with a golden key was equally impracticable. Access being impossible, I had the more time to spend at the shrine of our prophet, the tomb of Leuwenhoek. I next visited Paris, and procured an order to visit Sevres. Here, as the porcelain body is very dissimilar to ours, my motives were principally curiosity and the hope of gaining some knowledge of manipulation. After passing, with others, through the usually shown parts, on arriving at the end of the exhibition, the attendants informed me that my order desired them to show me all the other parts of the factory. To whose kindness I owe this advantage I know not. Thence to Berlin, scarcely knowing what to think or hope. Did the secret I sought lie in one word, or in one fact, or in a multitude of facts which I should not be able to comprehend even when told 1 The last was nearest the truth ; but I gathered and brought home with me the materials for thought and study, and it is the purpose of this paper to place before the Society the results. Now through Saxony to Dresden to visit Meissen, the scene of Bottischer's captivity, and the birthplace of all the 16 ON THE STRENGTH AND BEAUTY early European Porcelain. The journey did not end in disappointment. I knew that modern Dresden was not equal to old, either in the body or ornamen- tation, and I did not think to learn much. Yet I was unwilling to lose a chance, and, as the event proved, my visit was not in vain, for they exhibited some very curious modes of manipulations. My questions, however, were not answered ; hence I was obliged to trust to my eyes. Passing through Prague, I learned somewhat of glass-making. Thence to Vienna, where the value of Professor Hofmann's introduction was evinced in the kindness of Pro- fesssor Lowe, the Director of the Imperial Porcelain Factory. On learning my errand, he at once de- clared his willingness to tell me all he could, and I believe no one knows more. He devoted hours of his valuable time on several days, showing me everything in the works, giving me specimens — many of which are before the meeting this evening — directing my attention to books and to minerals we had not tried, and writing for me the addresses of persons or friends of his, from whom might be procured specimens. I cannot leave this part of my journey mthout mentioning the name of Dr. Heider, a member of our own profession, who has devoted much time to original research. Amongst his collections were many specimens of great interest, and from him I received many valuable suggestions. Amongst others to whom Dr. Lowe gave me letters OF MINERAL TEETH. 17 was Dr. Krantz, of Bonn, the well-known mine- ralogist. I need not tell you that to visit Dr. Krantz, necessitated a very long extra journey. I, therefore, felt that time and money should be economised. My time was all but expended ; I had now been from home two months, and therefore, anxious to save time, visited Dr. Krantz at the unusual hour of six o'clock in the morning. To him I am indebted for many facts hitherto unknown to me, and for many specimens of feldspar. From Bonn I revisited Paris, to procure spe- cimens of Limoges kaolin. Some little difficulty was encountered, but the director of the factory of Sevres told me he would send me specimens to England. I need not say he has done so ; they are on the table. On arriving again at home, no time was lost in arranging the store of information collected in my travels. It was obviously necessary to rebuild my furnace, which, in its present condition, did not furnish heat enough to prepare the materials as used at the factories I so recently visited. But, as I hope each department in porcelain work wiU form the subject of a separate paper, before dis- cussing the construction of furnaces, I may proceed to give a general outline of the plans adopted to solve the second proposition of my friend Dick, the solution of which I believe I have been so fortu- nate as to accomplish. 18 ON THE STRENGTH AND BEAUTY The usual materials employed by Dentists in the manufacture of mineral teeth are — feldspar, kaolin, or China clay, and silex in the form of quartz. These are the materials of true porcelain, with, in some instances, the addition of a little lime. True porcelain, however, is not yet made in England, because we have not native materials wherewith to form the saggers or muffles for baking it. Our fire-clays are not sufficiently infusible, and, there- fore, the English porcelain is composed of a mixture of kaolin, a plastic clay, generally blue clay, peg- matite, or Cornish stone, burnt bones, phosphate of lime, chalk flints, and steatite, or soap-stone. The amount of heat requisite for its production is much less than that required for true porcelain, and the body, when finished, not so hard and fine as that of the true product. In teeth-making the same diflferences exist. The melting point or amount of heat required in baking difi'ers in all the teeth we have now in use. Theoretically, those baked at the highest temperature should be the strongest, and, if all points of the various manu- facturing processes were conducted with equal care, doubtless, teeth requiring the highest heat would be the least affected by alteration of the same amount of temperature, although the great heat in their preparation is by no means a security if the ingredients are not of equal expansibility, or if the teeth are not well annealed, for then no OF MINERAL TEETH. 19 amount of high temperature employed in their manufacture will prevent them from cracking under the process of soldering ; while, on the contrary, teeth that almost melt under the blow-pipe, if they are composed of materials well assorted, are well made, rightly fired, and properly annealed, before they come to the Dentist, and are by him used, not abused, will stand very great and very sudden changes of temperature with impunity. There- fore, strength does not depend on height of tempe- rature used in making ; but my experience goes to show me that it greatly depends on the points last named, viz., the materials used should expand and contract equally ; while the body should be weU prepared, and the firing be with special care carried only to the point of giving a beautiful vitrified surface to the work, and not a degree beyond, or all the strength will be lost. The right amount of heat depends on the bodies, no two bodies re- quiring the same temperature ; and this is only to be learned by experiment. The temperature must, from its highest point, be let down as evenly and slowly as possible. These points attended to, a strong tooth is the result ; and I think, therefore, that teeth made without enamel — those fired at one heat — are likely to be the most durable. In the old French teeth, which you know it was almost impossible to crack in soldering, the strength arose from the body of the tooth being of strong opaque B 20 ON THE STRENGTH AND BEAUTY porcelain, not fired up to tlie point of vitrifica- tion, and covered ^ith a glaze well suited to the body, hut without regard to any natural efi'ect. I do not suppose many of you vriH make mineral teeth, but you may wish to make block-work or continuous gum, and the rules applicable to the making of teeth and the preparation of the materials are the same for all mineral work, and the prin- ciples once mastered, it is astonishing with what facility mineral teeth are used. I believe, in my workroom, my men would prefer to put a tooth thi'ough the fire to any other mode of fastening, for breakage so seldom occurs ; and the only means we use are those I beHeve constantly employed ; but we have hitherto (until the founding of this society) known so little of each other, that it is difficult to say what is generally done ; I must, therefore, limit myself to relating the plans used by myself. The piece is enclosed in plaster and sand, and put into an iron tray which is placed on the furnace till quite hot, the temperature rising gradually. The piece is then placed in the fire on the tray till it is aU quite red-hot, after which it is soldered with the blo"\\^ipe in the usual manner, and allowed to cool gradually. In this way very large pieces of blockwork may be soldered. The durabihty of mineral teeth also gi-eatly depends on their size and mode of fixing. I liave tried many arrangements for attaching the mineral tooth OF MINERAL TEETH. 21 to the plate. I inserted platina gauze in various forms into tlie back of the tooth. The strongest, but by far the most difficult to use, is a square gold pin, bent to follow the shape of the tooth, and soldered with gold to platina pins in the interior of the tube. This mode of fastening, which I think you will say is a most beautiful specimen of Dentistry, is the invention of a young lady. In very small teeth the gold back must be made to take all the pressure, as they generally give way in mastication ; very large teeth, on the contrary, are more liable to break in soldering. The posi- tion of the pins in half teeth is a matter of great consequence. The strongest form for general use is two good pins properly headed, placed one above the other in the length of the tooth, and it is of the first importance, that the pins be well embedded in the mineral- which of com'se should be as tough as possible ; and I would say that in all cases the base of the mineral should rest firmly on the gold plate in front, almost to the edge of the tooth, so that pressure from behind cannot bend the tooth outwards. Again, it is not possible for any mineral teeth to stand in the front of the mouth if the pressure in mastication is allowed to fall upon the back of them instead of upon the proper place. The molars, from their size will bear it with impunity if the teeth are good ; and as they are usually tube teeth, the 22 ON THE STRENGTH AND BEAUTY pin has not a cone of solder at its juncture with the plate to act as a wedge in the hole of the tooth, which is a common source of destruction. Vulcanite teeth stand best because they are not required to undergo great vicissitudes of temperature suddenly, and because they have necessarily a firm, good bed to rest on, but they are readily bitten out if the back do not protect the front teeth as they should do. I confess I totally ignored most of these points, thinking the mineral in fault, tiQ by experiment I found it quite the reverse. I have said the materials for making mineral teeth must be properly prepared, and I will endeavour to show how. First, of feldspar, which should be chosen quite free from quartz and other impurities, of as transpa- rent and uniform a quality as possible, and certainly from a source whence any required quantity can be procured, or otherwise you will never get two batches of body alike (see analysis of various spars). Make it red hot and plunge it into pure water. I may say at once the water used in all porcelain work should be distilled, for otherwise it may be a constant source of error. Now coarsely grind your spar in a Wedgwood mortar, and again it is most essential that the mortar should be veritable AVedgwood, or your body may become opaque or discoloured by mixture with the particles worn from your mortar by friction. Place the ground feldspar in a crucible, the most refractory you can get, and OF MINERAL TEETH. 23 melt it. This will require a very high temperature if the quantity is great, but it is a point of such importance that it cannot be omitted without great detriment to your ultimate product. I built a furnace on purpose to melt my spar ; it is circular, eighteen inches deep, by fifteen inches in diameter, with three inlets for air, and two exits, with a shaft of seventy-five feet, unbroken di-aft, eighteen inches in diameter ; and with this furnace the materials can be very readily melted ; in small quantities it can be done in any ordinary clay furnace. The melted spar will be very much more transparent than it was before, and more compact, besides it will enter more readily into combination with your other materials in your next firing. Break up your mass after it is cold, carefully grind ofi" all the portions of pot that stick to the spar ; again make it red hot, and plunge it in water preparatory to again grinding it fine enough for washing — a process by which all por(;elain materials are obtained of an equal degree of fineness. This process being well known I need not describe it. It has been said that the spar should be much coarser than the other ingredients, as it gives greater transparency. This may probably be the case, as that quality seems to depend on the transparent flux saturating the opaque body, as oil does paper. Under the microscope the two ingredients, kaolin and feldspar, can be clearly distinguished separate 24 ON THE STRENGTH AND BEAUTTY from each other, and the milky mass seems a trans- parent ground, mixed "v\ith an opaque ingredient. Elurenberg observes that it consists of articidated threads or little rods, which are interwoven, and cross each other in all directions. (According to the microscopic observations of Oschatz and Wachter, the porcelain mass consists of a vitreous matrix which is intersected in all directions by innumerable cr}'staline needles of the most minute dimensions, and its want of transparency is due to the reflection and refraction of the light from the surfaces of these cr}^stals.) This point I shall leave to the fancy of the user till more is known definitely. I use my spar rather coarser because I like to follow the recommendations of those who have had experience, and I have not yet had time to investigate the subject for myself. The clay and kaolin should also be washed, as it is very essential that these ingredients should be as fine as they can be obtained. Of clays, the blue clay is, in my opinion, the best for our purpose, because it imparts that pecuhar ivory-Hke appear- ance of the natural teeth which we so much require, and find so difficult to imitate. Clay and kaolin give strength, but they diminish transparency ; therefore, unless fluxed, can only be used in small quantities. The crystal should be the most transpa- rent. The optician's refuse is the best ; it consists generally of portions cut from fine clear stones, but OF MINERAL TEETH. 25 should be scrupulously washed immediately it is received, as it generally comes coated with emery — a mineral not desirable to us, though very useful to the optician. The rock crystal being heated to redness and plunged in water, is then easily reduced to a powder, though it is much harder than feldspar, and will require more time to grind. It should be the first material weighed for use, that it may be subjected to all the after grinding necessary for mixing the body. First, that it may be itself more comminuted, and also, as it assists in the grinding and mixing the other matters, especially the metallic oxides used for colouring. Quartz, or ground porce- lain, is to teeth what cement is to saggars ; it pre- vents shrinkage, and permits alterations of tempera- ture without cracking. It is, therefore, a very essen- tial ingredient : it also gives us more transparency and hardness, but it raises the point of heat required in baking, and as it is not plastic, it must have clay with it to enable us to mould. In casting this is overcome, but stiQ, till biscuited, the teeth without clay are very fragile, unless gum tragacanth, soap, or glue, or other matters be added. Lime, if used, may either be in the form of chalk, bone-ash, or gypsum : the quantity required must be accurately tested, and I think the only other caution necessary is, to be sure it is pm^e of its kind. It has been said that bodies containing lime bear change of temperature 26 ON THE STRENGTH AND BEAUTY better than those without it ; but this I think very- doubtful. Any other material, I need not say, must be reduced to fine powder by the means already de- scribed. AH the utensils should be earthenware, wood, or bone, and perfectly clean. It is curious to see how small an amount of extraneous matter, especially metallic oxide, will spoil the beauty of the work. I will now describe the compounding the body which I find a good one, that is, if the mate- rials used are like those shown to-night ; but from what I have said it will be evident that the quanti- ties must vary to suit every fresh supply of mineral, unless the new are chemically exactly like the old, which is seldom the case. oz. dwt. Tcoke of— Feldspar 3 4 Crj^stal 1 4 Blue Clay 6 RutileFrit 6 Mix for body, oz. dwt. gr. Take of— Feldspar 1 10 Crystal 6 Blue Clay 10 Cobalt Frit 6 Mix for point. The Colouring Frit — Rutile 1 dwt. Cobalt 2 gr. Spar 1 oz. Spar 1 oz. These teeth are very light tinted. The materials having been thus prepared, weigh dry, and make into a paste, if for moulding (the process usually employed), with distilled water in a OF MINERAL TEETH. 27 large mortar, and well mix ; even the order of doing tliis is essential — the crystal and colouring matter first, and ground for some time alone, then add the clay, and again grind them well together ; now the spar, portion by portion. In pouring, a process which gives very much extra strength, but which would occupy a whole evening for me to describe, the materials are made into a fluid slip, and poured liquid into the moulds, and should be all fritted together and re-ground. Time improves all bodies. After they are mixed, if they are kept damp, the more the dough is kneaded, to expel the air and solidify it the better ; there should be no air between the particles if it could be prevented ; and that tooth which is the most compact before baking will (all other points being equal) be the strongest after. I do not follow the usual plan of making the teeth, biscuiting them and enamelling afterwards. Having prepared my two kinds of mass, the one for points, the other for the body, I fiU both into the mould, the points first, the body after ; by this means they blend perfectly, and as the point mass is made a little more fusible, the efi'ect is a transparent tip or enamelled surface, and the markings on the enamel of the natural tooth are produced on the point as in the body ; this method, with accurate firing, produces, as you see in the teeth I now show, a very perfect resemblance to the natural enamel. They were moulded in the gutta-percha moulds I 28 ON THE STRENGTH AND BEAUTY handed to the President, and fii-ed by my pyrometer at a temperature which rendered them quite invisible through the test-door of my small furnace ; the heat was raised very evenly and slowly, and the teeth left untouched till the furnace was quite cold, from Saturday night to Monday morning. I would say of colouring materials, I think they should always be fritted, that is, a given quantity of oxide mixed with spar should be ground together very finely and vitrified ; on this mass being again groimd fine it can be more accurately weighed, and also the colour- ing power of the metal be more certainly known. In rutile, for instance, no two crystals will give exactly the same tint, but if fritted the whole is uniform ; and after vitrification the tint of colour can be well judged of. Thus the beauty and the strength are both attained. I shall go no further to night. To give the whole knowledge of mineral work would be quite impossible in one paper. I fear I have wearied you already; but if the subject has sufficient interest in your eyes, I shall be happy, next session, to continue my report, and to include all the varieties of block work and continuous gum, in which department I show you a few specimens, but in which the principles herein laid down for the making of teeth are more fully carried out, the larger and more complicated struc- ture requiring a higher development of our art. I know much has been done in block work by Mr. OF MINERAL TEETH. 29 Barkley, Mr. Heath, and others, and lately by Mr. Patrick, who is the first, I believe, who will teach its manipulation. I know his processes, and think them very good. The teeth now in use in England are much improved in shape, and also strength, since I began ; and for the latter quality, with proper treat- ment, do their duty very well. I cannot say so much for their natural appearance, although that is much improved, but I hope the use of the moulds I have described will become general, as there will then be no reason why the highest point of pecu- liarity in natural teeth should not be imitated — every maker has his own body, any of which will make good teeth, if care is used in treatment and firing. Gentlemen, it has been said in this room, and very truly, that some of the great physiological problems have been, and may be solved by Dentists. The problem I have endeavoured to demonstrate has been often solved, but we have been left again in dark- ness as to the solution. We read that the potters of Yesd, in Caramania, sent one day to the potters of Ispahan a vessel of porcelain, which would hold six English quarts of water, and weighed only half an ounce, and this of porcelain, that could be used for mortars and bullet moulds. "Wedgwood produced porcelain that would emit sparks when struck with steel, capable of receiv- ing a high polish, of resisting acids, and sustaining 30 ON THE STRENGTH AND BEAUTY a high temperature. Where are the formulae, the treatment of materials ? The materials themselves, what were they ? We may, perhaps, buy the vessels, but the facts of making are as much hidden now from the world as they were in the days of Bottischer. I trust a better light shines with us — the light of true science, whose rays not only illuminate the path of the present, but penetrate the darkness of the future, and last for all time. The specimens of materials used in the manufac- ture of porcelain which I have collected during my search, and which I have brought to show you, I intend for your museum. In begging your accept- ance of them, permit me to express a hope that they may be followed by the presentation of any mineral substances used in this manufacture that the mem- bers of this Society, spread over the surface of our globe, can procure, and I trust that the greatest care will always be used both to procure the specimens as fine and pure of their kind as possible, and to pre- serve them so for future use. In books a little dirt only spoils the appearance, and if they are misplaced they can be re-assorted, but in these things the least dirt or mixing spoils the whole. The President. — Gentlemen, we have heard from Mr. Truman a most instructive paper on the im- portant question of porcelain teeth-making — a sub- ject I have gone into myself with considerable enjoy- ment, but it is some few years since. I can quite bear OF MINERAL TEETH. 31 testimony to the difficulties the author has expressed in reference to the minerals to be employed, and the manner of using them ; and I can also bear testi- mony, to some extent, to the success which will attend any person who diligently pursues one course of experiments after another, until the desired result is obtained. Mr. Truman has persevered, and he has certainly, in the production of single teeth, surpassed anything I produced myself. But he has not given us any account of block teeth nor continuous gums — matters to which my own attention was more par- ticularly directed. I hope, however, at some future time, he will favour us with his opinions upon these subjects, for they are each of them very interesting and useful. I am quite sure if any member of the Society once enters fully into the subject of teeth- making, he will find himself amply rewarded. I do not know any pursuit more exciting than that of the production of porcelain teeth. You sometimes obtain very extraordinary and unexpected results. I recollect one batch of teeth I made came out per- fectly blue — why, I could not teU, nor am I able to discover to this day from whence the colouring matter came. You wiU have aU sorts of misadven- tures attending your efforts, until you have mastered the subject. If there is any gentleman here to-night who has devoted his attention to the question dis- cussed by the author of the paper, the Society wiU be glad to hear his remarks, and to profit by his 32 ON THE STRENGTH AND BEAUTY experience. I am quite sure Mr. Truman will be prepared to answer any questions which members of the Society may feel disposed to propose to him. Mr. Vasey (who w^as imperfectly heard) said the subject introduced to the attention of the Society was one in which he had had considerable practical experience. Mr. Truman's paper had been so com- plete as to render any further remarks upon the sub- ject almost superfluous. He (]\Ir. Vasey) had arrived at the same conclusion as that expressed by Mr. Truman with regard to a high temperature in the manufacture of teeth. He had come to that con- clusion after a great deal of labour. He considered it a most important point, and one the knowledge of which would save a large amount of time and uncertainty to experimentalists. Mr. Truman had mentioned, also, the difficulty he had felt for w^ant of a good pyrometer. No doubt, for want of time, ]\Ir. Truman had not described w^hat test he had used for proving when the teeth were sufficiently baked. — Mr. Vasey had found a piece of fine gold answer the purpose admirably. Mr. Truman. — Before answering Mr. Vasey, I must first thank the President for the very kind manner in which he has spoken of my efforts to perfect this subject. I know that he has had some experience, and 1 know that in most things he undertakes he is very enthusiastic, and I can very well imagine his delight in following out a OF MINERAL TEETH. 33 series of experiments of this kind. I am not at all astonished at the blue teeth, because smoke, except in the shape of a cigar, is by no means advantageous in teeth-making. I cannot at present answer Mr. Vasey's question as to the pyrometer. It is my intention, before long, to give it to the world in a proper form ; therefore, I know you will forgive me for not answering that question to night. The pyrometer proposed by Mr. Vasey, I may say, has been tried by my assistant, Mr. Eackstraw, and myself. And here let me say that one of the most essential points in this investigation, is an able and kind and patient assistant, and that I have certainly had in my friend James — most patient, most kind, most enduring, never put out, always striving for one end — to please me, and carry out our object. Still, I do not consider we are perfect in our manufacture of mineral teeth, that we should leave off, and say, "Now we have done all we have to do ;" because, although we can make strono- mineral teeth and natural-lookiner mineral teeth, we want to get this art so thoroughly understood by our workpeople and by ourselves, that teeth may be made so easily, and so readily and exactly, that we may be able to say in any particular case, " Make them of such a body and with such a formula," and produce exactly the kind of teeth required — until we arive at that point of perfection, our lal)our is not complete. 34 STRENGTH AND BEAUTY OF MINERAL TEETH. I do hope and think that the manufacturers have a great inclination to carry out these views with regard to the natural appearance of teeth. One of the great drawbacks has been that the neck of the natural tooth is so narrow, that mineral teeth so made, if mounted together, the space between the teeth at the base was so great, — we having no artificial gum to fill them, unless mineral gum, or gutta percha — ^neither of which were in general use —and such teeth were therefore unsaleable ; and that is one of the reasons why no manufacturer would attempt to make them. But now that we have the vulcanite — especially that beautiful pink vulcanite Mr. Ash has brought us to-night, with it we get a perfect gum, so that there is no longer any excuse for not producing teeth exactly to nature. Now they wiU be purchased ; and if they do not make them, we can make them ourselves. M'OOWAN AND DANK8, GREAT WINDMILL STKEET, HAYMABKKT. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. Form L9-116W1-8, '62 (0123788)444 .' ,".1, jK^.? E:'i^.:^'i■ x:^:^ ¥lV7'«f.,L'<"l