Cork: Its Origin and Industrial Uses

USES AND APPLICATION

MR. H. G. GLASSPOOLE,[31] writing regarding the uses of cork by the ancients, states: “The cork-tree, and the application of its bark to useful purposes, was well known to the Egyptians, Greeks and Romans. The former used this material in the construction of the coffins for their dead. Theophrastus, the Greek philosopher, who wrote on botany four centuries B.C., mentions this tree among the oaks, under the name of ‘Phellus’ in Book Two of his ‘Historia Plantarum,’ and stated that it was a native of the Pyrenees, having a thick fleshy bark which must be stripped off every three years to prevent it from perishing. He adds that it was so light as never to sink in water, and on that account might be used for many purposes.” It is the opinion of the writer that the attention of the ancients was undoubtedly called to this particular bark by its buoyancy, and as their fisheries were extensive its usefulness became readily apparent to float nets, etc., or to use even in the construction of their boats, and its sponginess and water-repellent properties not escaping their notice, it became a most likely material for stoppers of casks or amphorae as noted by Horace in Ode iii, 8: “Corticem adstrictum pice dimovebit amphorae.” Pliny, in his “Natural History,” XVI, 18, describes the tree under the name of Suber and relates everything said by Theophrastus of Phellus. From his account we learn that the Roman fishermen used it as floats to their nets and fishing tackle, and as buoys to their anchors. The use of these buoys in saving life appears to have been well known to the ancients, for Lucian, Epist. i, 17, mentions that when two men, one of whom had fallen into the sea, and another who jumped after to afford him assistance, both were saved by means of an anchor buoy. The use of this substance in assisting swimmers was not unknown to the Romans, for Plutarch in his Life of Camillus, who flourished in Rome 400 B.C., gives an account of its use by a messenger, sent to the Capitol, then besieged by the Gauls: “Pontius Cominius having dressed himself in mean attire under which he concealed some pieces of cork. He could not pass the river by the bridge, therefore took off his clothes, which he fastened upon his head, and having laid himself upon the pieces of cork swam over and reached the city.” The use of cork as stoppers was entirely unknown to the Romans, but instances of its being employed may be seen in Cato’s “De Re Rustica,” Cap. 120, but this did not happen frequently or more would be said of it.

The convivial customs of those days had no connection with the bottle, glass bottles being of a much later invention. Instead of having champagne or hock to be liberated from the bottle by the corkscrew at their feasts, the guests filled their drinking cups of gold, silver, crystal or beechwood from a two-handled amphora, a kind of earthenware pitcher, in which their choice wines used to be kept. The mouths of these vessels were stopped with wood and covered with a mastic, composed of pitch, chalk and oil to prevent air spoiling the wine or evaporation taking place. Columella, who wrote one of the earliest works on agriculture, gives directions for preparing this cement.

The employment of cork for stoppers of bottles appears to have come into use about the seventeenth century, when glass bottles, of which no mention is made before the fifteenth century, began to be generally introduced. Before that period apothecaries used stoppers of wax, which were not only much more expensive but far more troublesome. In 1553, when C. Stephanus wrote his “Praedium Rusticum,” cork stoppers appear to have been very little known in France, for he states that this material was used principally for soles in that country. It is not known when cork and corks began to be generally used, but in that very amusing and instructive diary of Mr. Samuel Pepys the following entry is found: “14 July 1666” After having written to the Duke of York for money for the fleet, I went down Thames Street and there agreed for four or five tons of cork to be sent to the fleet, being a new device to make barricados with instead of junts (old cable),” but he does not inform us how the material answered.[32]

In Evelyn’s time (1664) cork was much used by old persons for linings to the soles of their shoes, whence the German name for it, “Pantoffelholtz” or slipper wood. The Venetian dames, Evelyn says, used it for their choppings or high-heeled shoes to make them appear taller than nature intended they should be. The poor of Spain lay planks of cork by their bedside to tread on instead of carpets. Sometimes they line the inside of their houses, built with stone, with this bark, which renders them very warm and corrects the moisture of the air. Loudon relates that in the celebrated convent at Cintra, Portugal, several articles of furniture are made of this tree. Virgin cork, or the first bark of the tree, is now very much used for window flower boxes, grottoes, etc., while the subsequent grades are used for small architectural and geognostic models. Cork was formerly employed in medicine even as far back as the time of Pliny, as he tells us that the bark of the cork tree, pulverized and taken in warm water, arrests hemorrhage at the mouth and nostrils, and the ashes of it taken in warm wine are highly extolled as a cure for spitting blood (see Pliny, “Nat. Hist.” b. 124). In modern time powdered cork has been applied as a styptic and hung about the necks of nurses. It was thought to possess the power of stopping the secretion of milk. Burnt cork mixed with sugar of lead has been used as an application to piles. See Pereira’s “Materia Medica.”

Ground cork and India rubber formed the basis of Kamptulicon, the soft unresounding material which covered the floor of the reading rooms of the British Museum.” In further describing the many uses to which cork is applied, reference is made to the résumé of Mr. Good in “La Nature,” which is incorporated with a few slight changes.

“The various applications of cork that we are now going to pass in review are worthy of description, as each of such applications has its raison d’être in one or more of the physical or chemical properties of cork bark. The manufacture of stoppers utilizes, in the first place, the impermeability of the bark, and, in the second, the latter’s elasticity and imputrescibility, the remarkable lightness playing no rôle therein.

Before entering upon a study of the industrial applications of cork, in grouping them according to the various qualities of this product, we must return to the “male” cork, derived from the first barking of the tree. It has been said, because of its slight elasticity and numerous fissures, this product has but little commercial value, and shall have mentioned its principal application when we have stated that it is used in the decoration of parks and gardens. An endeavor has been made, but without success, to manufacture from it, mills for decorticating rice.

Certain parts of it can be converted into small stoppers. In the country where it is produced, it is used for making water conduits, beehives and shelves on which to preserve objects from dampness. Mixed with a mortar of clay, the Kabyles use it for the walls of their dwellings, and also, in lieu of tiles, as a roofing material for their primitive habitations. It is used also by fishermen as floats for their nets.

These various applications were known to the Greeks and Romans, as shown by the works of Theophrastus and Pliny. The latter says of the cork-oak: “Nothing is utilized but its bark, which is very thick, and which is renewed in measure as it is removed. This bark is often used for the buoys of anchors and ships and of fishermen’s nets, for the bungs of casks, and for women’s winter foot gear. The Greeks called the cork-oak the ‘bark tree’.... Cork bark is used as a covering for roofs.” (“Hist. Nat.,” xvi, 18.) As for the chips, they can be used as an isolating material to prevent freezing. Reduced to fragments, they furnish an excellent material for covering circus rings.

Let us return to “female” cork, which is much better adapted for being worked, and the grain of which is much more homogeneous. In this form cork bark constitutes a very bad conductor of heat and sound, and renders valuable services in the industries as a material for preventing the cooling of steam pipes and generators, and preventing the melting of ice in ice houses, or the heating of apparatus for producing cold.

It is the basis of a certain number of cements, and coatings for preventing the escape of heat, which are applied to pipes, steam domes, hot water reservoirs, etc., and upon the composition of which we shall not dwell here. As for jacketing with cork alone; the first method consists in placing narrow strips of cork, whose edges touch each other, along steam pipes and cylinders, and fastening them by means of wire. A pipe thus jacketed is tangent internally to all these strips, and a section of the whole shows a circle inscribed in a polygon. In the second system thin strips of cork, fastened to canvas with India rubber cement, are wound around the pipe spirally. Finally, a third method of jacketing consists in the use of two half cylinders that exactly fit the exterior of the steam pipe. These cylinders, which can be made of any desired length, are made of powdered cork and starch, and are covered with a spirally wound strip of calico, which may be coated with tar or any suitable kind of paint. Each of these systems permits of obtaining a great saving in fuel.

As cork is likewise a very bad conductor of sound, it is successfully used on the doors of consulting rooms, and for making floors for hospitals, etc. Finally, in the manufacture of certain stringed instruments, it is used to prevent a loss of sound.

The slight density of cork, as compared with water, and its impermeability to liquids, make it an excellent float, capable not only of remaining on the surface, but also of supporting quite heavy bodies thereon. We shall be content to mention the annular cork float used in night lamps, the square block in which bath thermometers are fixed, and the fisherman’s dobber.

It is cork, too, that is used by preference in the manufacture of swimming and life-saving apparatus, to which inventors have devoted much thought. Very many vessels are provided with cork mattresses, which, in cases of shipwreck, render the greatest services. For example, the ship Constant, which sailed from Anvers for Brazil in 1845, was wrecked on the night of October 12th, at twelve miles from St. Thanes, but, thanks to the cork life preservers and mattresses that she had on board, not one of the crew was lost. As for life-saving buoys, properly so called, they consist of several cork planks which are given an annular form, and are provided with free ropes that are knotted here and there so that they may be easily grasped. From the stern of every vessel a buoy of this kind is suspended by a rope that may be at once cut when the cry of “A man overboard!” is heard. These buoys are usually covered with canvas coated with a paint that serves to preserve it. It is also possible to save a person who has fallen into the water at a certain distance from a wharf by means of floats. This device consists of a piece of rattan provided with points around which molten lead has been poured, and the whole is then surrounded with cork in chips, and covered externally with canvas and a network to protect the affair against wear.

Fenders are canvas bags that are filled with cork and are placed along the sides of ships or along docks in order to deaden the shock in case of a collision. Such are the principal uses rendered to navigation by cork.

It has already been seen, by the extract from Pliny, that Roman ladies preserved their feet from cold by means of cork soles. Such a use of cork is still in vogue. In addition to these soles, which are flat, there are others that have nothing to do with hygiene, and are merely connected with fashion. Such are the Louis Quatorze talonettes, designed to increase the stature without exaggerating the heel of the shoe. Female dancers wear linings of this kind in their shoes, which, as well known, have flat soles. A thin sheet of cork enclosed in the sole of the shoe would, we think, prove very useful to troops on a march during bad weather.

Cork is not only useful as an application to foot gear, but also renders great service in head gear, and, in the form of helmets, has preserved a large number of soldiers from death by sunstroke in tropical countries. We find it again, in the form of very thin sheets, in the interior of beaver hats, where it is used as a protection against heat. It is also used in these same hats as a sweat band, in lieu of leather. In ladies’ toilets, the cork serves to make the carcasses of the birds that decorate their head gear. Manufacturers of dress trimmings use cork molds, which they cover with silk or cotton, for ornamenting cloaks, etc. The lightness of cork can alone explain the great size of these balls, olives, etc., some of which are larger than a hen’s egg.

A few years ago, a Paris house sold cork cravats, and we have recently seen, exposed in a show case, some children’s costumes, in which the sailor’s collar was of thin sheet cork decorated with colored designs. Although cork gowns have not yet appeared, we have waterproofs composed of thin sheet cork cemented between two pieces of silk. These cloaks have the advantage over those made of rubber of not allowing air to pass through them.

There is also a curious application of cork in the manufacture of a fabric that renders those who are clothed with it insubmergible.

We can mention but few of the many applications of cork, new ones of which are being discovered every day, so shall confine ourselves to recalling the services rendered by this valuable product in surgical prosthesis and for the use of naturalists, etc. In domestic life, it is used for bath steps, and for making rolling pins for crushing almonds without absorbing the oils as wood would do. Thin sheets of it are used for making fancy labels for wines. The ease with which it may be cut, turned and worked causes it to be employed in the manufacture of small objects, such as rural landscapes and the reproductions of monuments, some of which are genuine works of art. We may likewise mention, among objects made of cork, cases of various forms for sending bottles by mail, spools for allowing of the cheap carriage of silk, the old-fashioned inkstand, the thick penholder for preventing writer’s cramp, the cigar holder and many fancy objects that would take too long to enumerate. There is perhaps no calling that does not have to make more or less use of cork. Polishers of gold have used it from time immemorial, in the form of narrow strips, for rubbing their work with rouge. The wheels with which crystals are polished are faced with it, and watchmaker’s lens mounted in cork, the lightness of which prevents the muscles of the face from tiring.

In the industries, driving pulleys are now beginning to be provided with cork in order to secure an adhesion of the belting. In carpenter shops these bands of cork are now advantageously replacing rubber ones for covering the pulleys over which the band saw runs. The stoppers of nursing bottles are now being replaced by hygienic ones of cork, which, being very cheap, can be changed as soon as the presence of ferments is suspected. Cork is likewise employed in the manufacture of children’s toys; it serves, for example, for fixing the wig on dolls’ heads. Is it necessary to recall the cork of pop-guns and pistols, and the cork battledores and shuttlecocks used for playing with indoors? These few data will serve to show that but few products are capable of so many diverse applications as cork is; and the question may be asked whether it would be possible to substitute anything else for it, in case the supply should become exhausted.

The manufacture of stoppers and of the various objects that we have just enumerated furnishes a considerable quantity of chips, which along with the waste derived from the collecting of the material, and with old, second-hand corks, constitutes the crude material destined to supply certain important industries, which, for the sake of completeness, must be mentioned.

We have first the cork powder industry, which manufactures powders of various degrees of fineness. The coarsest powder is used for packing fragile objects, on account of its elasticity, coupled with its lightness, which permits of a great saving in freight charges.

The finest powder forms, “liegine” or “suberine,” whose balsamic properties are well known to hygienists, and which may be used as a substitute for lycopodium, starch and fecula as an application to the skin of babes. Under the name of “zifa powder,” an insect powder has been made composed of cork and phenol. Fire lighters have likewise been made from cork powder; but this and the last named application have not amounted to much.

We cannot enter into much detail in regard to the manufacture of linoleum, notwithstanding the interest that it presents. The manufacture began in Scotland, and is tending to settle in our own country. Linoleum is made by intimately mixing cork powder with oxidized linseed oil. The paste thus prepared is spread over canvas if the intention is to manufacture carpets, but over paper if it is desired to make hangings. The color of linoleum, which is the same as that of cork, only a shade darker, can be enlivened by colored designs. When applied to damp walls, linoleum is capable of receiving oil paintings of a more stable nature than those executed upon wood, which warps, or upon other building materials, which crack, such as plaster, for example. It can also be used for decorated ceilings for public halls, cafes, etc.; and when such ceilings become black through smoke and dust, they can be washed.

As a carpet, linoleum renders flooring perfectly insonorous. It converts damp and unhealthy apartments into healthy and warm places of habitation. Used in kitchens and offices, it has the advantage of not being spotted by fatty matters. It has been generally adopted in our naval and merchant ships, where the use of it has given a great setback to the oil cloth industry.

A new decorative product, “lino-burgau,” obtained by embossing linoleum, possesses the iridescent reflections of nacre, due to the application of colored varnish along with a bronzing of certain parts. Notwithstanding its expensive nature, we believe that there is a great future in store for it.

The manufacture of agglomerates of cork is becoming very widespread in France. We have already mentioned the use of artificial cork for jacketing steam pipes, and we have stated that this product is obtained by mixing cork powder and starch under pressure. This dried paste can be given the most diverse forms, and be made of any thickness. Another substance, called brick paste, is obtained by mixing the coarsest cork powder with milk of lime, and, after compression and drying, constitutes, under the form of bricks and slabs, an excellent material for the construction of party walls, for covering damp walls and sloping roofs.

In the cellars of breweries, these bricks diminish the melting of the ice. In gunpowder works, they prevent the caking of the powder through dampness, and, in case of an explosion, their friability and lightness lessen the importance of the catastrophe. They are also used as a foundation for flooring in order to destroy its disagreeable sonorousness. In the spinning mills of Alsace and the west of France, they have given excellent results, both as regards their resistance to the passage of sound, heat and cold, and their cheapness.

Cork chips and waste, when distilled, furnish an illuminating gas that burns with more brilliancy than that made from coal, and does not, like the latter, give off sulphureous emanations that tarnish frames and other gilded objects. The city of Nerac was lighted with cork gas for a certain length of time, but the use of it had to be given up on account of the difficulty of storing the chips, which, with but little weight, took up an enormous space. This gas, in view of its slight density and its purity, would prove an excellent one for the inflation of balloons.

Finally, cork parings and waste, properly carbonized, produce Spanish or cork black, one of the most beautiful and durable blacks known in painting.”

The recent uses for corkwood are, as a float in the carburetter of an automobile, the cork insert in the periphery of a pulley,[33] cork paper for cigarette tips, a wadding for shot-gun cartridges, cork-coated fabric for balloons, as a filling for automobile tires, as a disk in the non-refillable bottle, for the making of casks and barrels in which to store wine, and the ground cork wood for shipping fruit, etc. in, to prevent spoiling.

Substitutes

Of course, no matter what the substance, a substitute is always sought for, and this has been the case with cork, but with very unfruitful results. “A primitive material used for bottle stoppers consisted of the roots of liquorice; the spongy substance of another tree called ‘Spondies Lutea,’ which abounds throughout the marshy regions of South America and there called ‘Monbia,’ was also used in the same way, as also a product called ‘Myssa,’ which contains some of the elements of cork.[34] Another substitute is mentioned in Henley’s “Twentieth Century Receipts” as follows: Wood pulp three parts; cornstarch pith one part; gelatin one part; glycerine one part; water four parts; 20 per cent solution formic aldehyde; and still another in the “Handyman’s ‘Inquire Within,’” by Haslock, called “Phellosene,” a French invention consisting of powdered cork mixed with a solution of nitro-cellulose in acetone: compressed and dried. The wood of Anona palustris growing in the West Indies, and called the alligator’s apple, is used by the negroes to stop their jugs and calabashes also, and a Mr. Brockedon invented a substitute as noted in “Knight’s Cyclopedia,” the core of which was cotton twisted into strands, wound with flax and the whole covered with India rubber. Cork’s competitor in buoyancy, “balsa wood,” is in no wise constituted to take its place, although 20 per cent lighter; as it is a fibrous growth and hygroscopic, requiring a coat of water-proofing solution before it can be used even for life-preservers; rubber, its close second, in the manufacture of stoppers is not to be compared with it, and although there have been many patent devices for sealing bottles, such as the porcelain stopper, crimped metal stoppers, etc., the cork stopper still reigns as the best of them all.

MANUFACTURE

IN describing the manner and process of converting the corkwood into the various commercial forms, no attempt will be made to give a scientific exposition of all the details, as being inconsistent with the character of this monograph, nor will any other processes be described than the ones in which the material being worked, is cork. This may exclude much of interest to the reader, but the intent of this little work is purely a corkwood exposition, and the desire to keep it so must prevail.

In taking up the processes of manipulation we naturally start from the beginning, but the beginning in this case has a peculiar significance as relating to the whole, for it is apparent to utilize corkwood to the fullest extent its qualities must be studied and the best, used first, so that the beginning of the corkwood industry is peculiar in this fact, that it takes the best part and leaves but scrap, which must be studied carefully to realize the value lost in the first process; therefore, in the manufacture of one article of corkwood it is necessary to make provision for the scrap created, and this is a characteristic of all such establishments.

Raw Stock

The baled cork, as received, is our first consideration, for its bulk, being out of all proportion to its value, attracts the attention at once.

As in all business where the raw stock is conveyed from a distance and there is a possibility of delay in shipments, a large stock must necessarily be kept on hand, and this feature is very pronounced in and about a “cork factory.” Great piles appear in the open or within large sheds, covering much space, and sometimes in the factory itself.

This stock is carefully watched and care taken to keep it large enough to supply all needs for a long time as a shortage in raw material would not only mean no work, but the loss of business, due to the inability to supply first-grade material, for this is the prime factor, the various other grades being compelled to await a favorable market. Appended is a diagram that will give some idea of the utilization of corkwood.

The corkwood bale as received, measures as a general rule 2′ × 2′7″ × 4′ and is securely strapped with iron bands about one inch in width and a thickness of ¹⁄₁₆″ to ¹⁄₃₂″, and the weight depending upon the quality of corkwood ranging from 150 pounds to 200 pounds per bale.

Sorting

The first operation, that is, the first thing done with the corkwood, is the sorting. This is becoming more important as the uses of cork increase, as various grades can be used for so many particular things now, without the necessity of being called a by-product; but the principal divisions are: superfine, fine, common and coarse.

These of course are now extended to many classes, and is resulting in careful scrutiny of the shipments and stock, the sorter becoming an expert, and an increasing factor in the business. His knowledge not only including the grades of corkwood, but the uses to which the various grades may be put so that waste is avoided and the full value gotten out of all.

Cork Stopper Making

After the sorting, the slabs are placed in steam boxes and subjected to a steam bath, which it is claimed softens the material and also prepares it for the scraper, who cleans and removes the dirt and callous or “raspa” accumulated in its mountain home. This scraping is done either by hand or machine, the handwork being done with a short handle, curved bladed knife called a “doladera,” raspador or raspeta: a workman being able to scrape from two to three metric quintals of cork in a day, or ten hours. The scraper machine being a vertical steel shaft carrying several knives placed at a very slight helix and making about 1400 revolutions per minute and will scrape from ten to twelve metric quintals[35] per day or ten hours. Cutting the slabs into strips or fillets (tiras ó’rebanadas) is the next step. These strips, the width of which is equal to the length of the cork to be cut, as the cutting is done across and not with the grain, were formerly cut by hand with a knife having a flat surface and curved edge called “cuchilla de rebanar,” but now replaced by the circular knife, which operates the same as a rip-saw. From here the strips go to the stopper-makers’ punches or blocking machines. This machine has a rotating tubular die with sharpened edges of the diameter of the cork to be cut, made to revolve about two thousand revolutions per minute, the operator having a foot lever attachment which permits him to thrust the die through the strips of cork as he holds it against a resisting piece parallel with the operating plane of the die. Thus, he can punch out many thousands of corks a day, the noise of the punches being a very characteristic sound in all such establishments. The operator, of course, must use care to avoid defective spots in the bark, and also to cut the corks out as closely together as possible so as to reduce waste to a minimum. For it is here that the cork manufacturer seems to lay his particular lament. If he could but make his corks the sizes most in demand, ship them and thereby do a business that would clearly figure up the year’s work, and perhaps keep a surplus on hand for unexpected orders. But this he cannot do, for almost every cork he cuts there is enough waste material to make three or four smaller sizes, and this he fain would discard if it were not for the possible profit there is in it; and consequently in almost every cork factory will be found a large surplus stock of all sizes, and the owner anxiously hoping that some one will take them off his hands.

The stoppers which come from these machines are round with parallel sides. If tapered corks are desired, larger at the upper end than at the lower, the cylindrical or straight pieces must be passed through another machine which handles them deftly, holding them against the edge of another circular knife; seemingly motionless, the only outward indication of the speed with which the keen blade is revolving being a delicate shaving which curls upward for an instant, and then is drawn away by air suction to the waste bin, where this material is all collected and used in various, useful ways as will be shown later. In cutting the corks, although care is exercised, many will be imperfect and defective, and in order to utilize them they are cut into smaller sizes by men who sit at low tables and deftly handle the sharp-edged knife, which with one stroke reduces the cork to the size that it can fill, using a scale which is apparently standard with all cork dealers.

The general standard of corks or stoppers, known as the United States standard, is as follows:

This classification of necessity applies to the trade and gives a size for almost any character of work there is, though another general classification that is used principally abroad, is as follows:—

Thick corks having more than 31 millimeters[36] in diameter.
Ordinary or commercial, from 25 to 31 millimeters.
Bastard corks, from 23 to 25 millimeters.
Thin corks, having less than 23 millimeters.

These classes of sizes are of course divided again and again by the manufacturers. To this size classification must be added a quality distinction, and this generally takes the same as before described, in sorting the cork-board, grading down from the best which is tawny or pink in color, with a fine texture, free from cracks, stone cells, or other blemishes.

As has been stated, the punch is now employed in most corkwood establishments, but there are still a few who do the work by hand and maintain that the best results are obtained in this manner.

Hand-cut corks or stoppers are used mostly for the high-class wine trade and are a little more expensive than machine cut. There is also a hand machine for shaping corks, which consists of a knife, the blade of which is placed horizontally, joined generally to a piece of wood, to which a back and forward movement is given similar to that of a carpenter’s plane. In moving, the knife turns the square cork, or whatever shape it may be, by a series of belt attachments, and takes off a strip of cork (palilla) more or less thick, according to the distance from the axis of the cork and the edge of the blade; the principle being the same in the power machine, if these are parallel the resulting cork will be cylindrical, and if not, it becomes conical.

The standard size stopper is the prime use to which corkwood has been put, and in the making of it the best material is used; this material coming in varying thicknesses, it sometimes is difficult to secure enough for making “champagnes,” so some manufacturers produce a stopper that answers the requirements by fastening two pieces of thin superfine corkwood together with a rubber cement made by dissolving pure Para rubber in disulphide of carbon, which makes a very good binder and not lessening the quality service to any appreciable degree.

After the corks are cut, the ends are not always as even and as smooth as desired, so they are taken to a sandpaper wheel which revolves very rapidly in an upright position, and against this the corks are held for a few seconds until the surface becomes smooth and straight, the dust created being collected and used in various ways. (See “Waste Utilization.”)

Cork-disk Making

(See “Waste Utilization”)

Since the Crown Seal stopper, for beer bottles particularly, has come into vogue, there has been a great demand for cork disks which form the medium for air tightness and this has given the cork-worker an opportunity to utilize a grade of corkwood that usually had but little commercial value, that is, a thin bark.

It may be well to state here for the uninitiated that the Crown Seal is made up of a tin cap, corrugated on the lapped edge, for gripping the top of the bottle, a corkwood disk and a water-proof paper between the disk and cap, a very ingenious device.

As you have already read in a previous chapter that corks are cut vertical parallel, or, to state more clearly, the axis of the stopper must be parallel with the axis of the tree that furnished the bark; and the desired direction is easily recognizable by the colored striae due to the annual layers of suberous substance that are observed in the direction of its axis, this rule being followed because cork is found to be more impervious to liquids if cut in this manner. It will be readily seen that if disks are cut horizontally parallel, that is, the annual layers running at right angles to the axis of the disk, this grade of cork can be utilized to great advantage. The mode of cutting is by a horizontal revolving blade, which slices the cork to the desired thickness, usually a quarter of an inch, and then it follows the usual course of punching, etc. From these operations a great deal of waste accumulates, and this would be a great loss if methods were not devised for its utilization. Many firms work up this waste on the premises, but most of it is shipped out and its conversion forms a separate part of the corkwood industry, which will be described later. We might say now that the cork is made, for it has been cut and shaped into the desired commercial size; and all that remains is to sort them and ship them away. But if commerce desires sizes and quality, it has also exacted many other requirements of a cork before it is acceptable and we will now take up the further manipulation of cork before it leaves the factory. Naturally, this corkwood, coming such a distance and being handled by so many in the general processes just described, gets more or less dirty, and aside from that perhaps in the growing the tissue has not remained as white as is desired, so before the cork can leave the factory it has to be washed or cleaned. And in this washing I will not say that there is not an attempt to improve the looks of the corks in order to get a better price. Now this washing or bleaching is carried on in the simplest manner and is just soaking the corks in water and a chemical and then placing them in a centrifugal spinner, which is nothing more than a perforated receptacle made to revolve within an iron jacket, which is connected to a drain, naturally forcing the material against the periphery and thereby causing the excess water and acid to pass out through the perforations, this system becoming quite common in cork factories to-day, greatly facilitating the drying, which is done mostly by the atmosphere. This is all there is to the mechanical part, but curiosity prompts us to inquire what chemicals are used to clean the corks, so I have ascertained the principal ones, but of course every manufacturer will have his own way of doing this part of the work, although the principle remains the same. An old way was to wash them in water containing chloride of tin or oxalic acid and then subjecting them to the fumes of burning sulphur, but the sulphur bleach has been discontinued. Bioxalate of potash has also been used in solution, as also chloride of lime, ammonia and sulphuric acid. Another way is to wash in a 10 per cent solution of hydrochloric acid and then immerse in a solution of sodium hyposulphate and hydrochloric acid, finally washing with a solution of soda and water. All of these produce the desired effect when mere cleaning and bleaching is all that is required: but in the poorer grade of cork, mostly a thick cork that has been jaspered or contains micro-organisms, a system of treatment with formol or methylal, ethyl alcohol or spirit wine and formaldehyde and impregnating with casein has been used. These bleaches are applied to regular stoppers and disks alike, but in addition to this the disks are given a bath of hot paraffin, or glycerine and paraffin, which improves their resistance and retards discoloration. This generally being done in a steam-jacketed kettle, or tumbling barrel, and then placed in a centrifugal to remove the excess of water and paraffin.

In some factories, and when the customer requests it, the name is branded upon the stopper by irons heated by gas, gasolene or in a coal fire, automatic gas heated machines being most general.

In the foregoing it has been shown how the stopper and disk are made, and although there are many different manufacturers of corkwood stoppers, it will be found that the modus operandi just described is followed generally, with perhaps a variation in the details. The waste material, “recortes” as stated is collected and used in various ways, but either in conjunction with other materials or alone in a granulated or powdered state.

The following chapter will enumerate the three principal uses of waste corkwood, and as these cover the fundamentals of the other uses it will not be necessary to describe them, e.g., linoleum, made by mixing cork-flour and linseed oil.

WASTE UTILIZATION

In giving the processes of the methods used in the conversion of the corkwood waste and virgin corkwood, which is classed as waste, it will not be possible to go too far into the details, as most of them are secret, and in justice to those who use them a résumé is all that will be incorporated in this monograph. But this will give a good idea and understanding of the utilization, which is all that is intended. As in the first processes of corkwood manipulation the best is taken first; so, in the department of waste utilization, a process is now used whereby the best scrap is made into cork disks for the Crown seal as described, and serves its purpose well.

This scrap is taken and granulated in an iron rotary cutter mill, to a degree of fineness that will pass a ¹⁄₈″ mesh, it is then screened and mixed with a secret binder that has a wonderful holding quality; it is then dried by steam and pressed into sheets by hydraulic presses, dried again, and then stamped out in the usual manner. There is no waste to this process as the unused portions go back to the grinders again and through the usual process.

Granulated cork is made by grinding the waste in ordinary metal roller, cage or bur mills, and then screening same for the various degrees of fineness; if cork-flour is desired, a tube mill may be used.

These two uses are generally confined to the best scrap, but there still remains a large quantity which has a great value. A portion of this is made into Spanish black by carbonizing same in a closed iron kettle, or retort, and then grinding same in a regulation ball mill, until the desired fineness is obtained; this process producing a very fine black.

The above uses in no degree exhaust the amount of scrap corkwood that leaves the various factories here and abroad, nor is its usefulness expended, for there is one use to which cork scrap is being put that bids fair to rival the stopper industry in importance, and that is in the form of cork-board for insulating purposes.

The processes for the making of cork-board differ in many ways, widely divergent in principle. The corkwood waste and virgin cork are broken up and chipped in an ordinary iron mill as a preliminary to all processes; in one, claimed to be the best, this chipped material is poured into iron molds the desired shape of the slab, subjected to heavy pressure and run into an oven kept at about 800 to 900 degrees Fahrenheit. This oven, being a low brick type, resembling a lear and heated by coal fires, the slab molds being drawn through on an endless chain, which runs at a speed to keep the cork in just long enough, for the resin in same to exude and bind the little particles together; the cork is also charred in this process, thereby converting it into a carbonized cellulose which makes it an excellent material for insulation. Steam-heated hydraulic presses are also used for making small tile, etc., being the same principle as above, without the charring.

The other process involves the use of tar, pitch or asphaltum, as a binder for the cork particles, and in one, the cork is mixed with a clay before being mixed with the asphaltum. The binder being heated in steam jacketed kettles, and in one it is mixed in the proportion of one to four, while in the other it is forced into the mass under pressure and then drawn out again by vacuum, both mixtures being poured into molds of the desired shape of the slab or in large molds, to be cut up after, and subjected to heavy pressure, the sawing being done by an ordinary rip-saw, cutting the block into any desired thickness of slab.

The above described processes do not include all of the various manipulations of corkwood, for there are innumerable things as stated under the “Uses” for which there is a necessity of mechanical operation, in their making; but the general processes are as stated and will cover most all.