De Re Metallica Part 54

Aluminous rock is first roasted in a furnace similar to a lime kiln. At the bottom of the kiln a vaulted fireplace is made of the same kind of rock; the remainder of the empty part of the kiln is then entirely filled with the same aluminous rocks. Then they are heated with fire until they are red hot and have exhaled their sulphurous fumes, which occurs, according to their divers nature, within the s.p.a.ce of ten, eleven, twelve, or more hours. One thing the master must guard against most of all is not to roast the rock either too much or too little, for on the one hand they would not soften when sprinkled with water, and on the other they either would be too hard or would crumble into ashes; from neither would much alum be obtained, for the strength which they have would be decreased. When the rocks are cooled they are drawn out and conveyed into an open s.p.a.ce, where they are piled one upon the other in heaps fifty feet long, eight feet wide, and four feet high, which are sprinkled for forty days with water carried in deep ladles. In spring the sprinkling is done both morning and evening, and in summer at noon besides. After being moistened for this length of time the rocks begin to fall to pieces like slaked lime, and there originates a certain new material of the future alum, which is soft and similar to the _liquidae medullae_ found in the rocks. It is white if the stone was white before it was roasted, and rose-coloured if red was mixed with the white; from the former, white alum is obtained, and from the latter, rose-coloured.

A round furnace is made, the lower part of which, in order to be able to endure the force of the heat, is made of rock that neither melts nor crumbles to powder by the fire. It is constructed in the form of a basket, the walls of which are two feet high, made of the same rock. On these walls rests a large round caldron made of copper plates, which is concave at the bottom, where it is eight feet in diameter. In the empty s.p.a.ce under the bottom they place the wood to be kindled with fire.

Around the edge of the bottom of the caldron, rock is built in cone-shaped, and the diameter of the bottom of the rock structure is seven feet, and of the top ten feet; it is eight feet deep. The inside, after being rubbed over with oil, is covered with cement, so that it may be able to hold boiling water; the cement is composed of fresh lime, of which the lumps are slaked with wine, of iron-scales, and of sea-snails, ground and mixed with the white of eggs and oil. The edges of the caldron are surmounted with a circle of wood a foot thick and half a foot high, on which the workmen rest the wooden shovels with which they cleanse the water of earth and of the undissolved lumps of rock that remain at the bottom of the caldron. The caldron, being thus prepared, is entirely filled through a launder with water, and this is boiled with a fierce fire until it bubbles. Then little by little eight wheelbarrow loads of the material, composed of roasted rock moistened with water, are gradually emptied into the caldron by four workmen, who, with their shovels which reach to the bottom, keep the material stirred and mixed with water, and by the same means they lift the lumps of undissolved rock out of the caldron. In this manner the material is thrown in, in three or four lots, at intervals of two or three hours more or less; during these intervals, the water, which has been cooled by the rock and material, again begins to boil. The water, when sufficiently purified and ready to congeal, is ladled out and run off with launders into thirty troughs. These troughs are made of oak, holm oak, or Turkey oak; their interior is six feet long, five feet deep, and four feet wide. In these the water congeals and condenses into alum, in the spring in the s.p.a.ce of four days, and in summer in six days. Afterward the holes at the bottom of the oak troughs being opened, the water which has not congealed is drawn off into buckets and poured back into the caldron; or it may be preserved in empty troughs, so that the master of the workmen, having seen it, may order his helpers to pour it into the caldron, for the water which is not altogether wanting in alum, is considered better than that which has none at all. Then the alum is hewn out with a knife or a chisel. It is thick and excellent according to the strength of the rock, either white or pink according to the colour of the rock. The earthy powder, which remains three to four digits thick as the residue of the alum at the bottom of the trough is again thrown into the caldron and boiled with fresh aluminous material. Lastly, the alum cut out is washed, and dried, and sold.

Alum is also made from crude pyrites and other aluminous mixtures. It is first roasted in an enclosed area; then, after being exposed for some months to the air in order to soften it, it is thrown into vats and dissolved. After this the solution is poured into the leaden rectangular pans and boiled until it condenses into alum. The pyrites and other stones which are not mixed with alum alone, but which also contain vitriol, as is most usually the case, are both treated in the manner which I have already described. Finally, if metal is contained in the pyrites and other rock, this material must be dried, and from it either gold, silver, or copper is made in a furnace.

Vitriol[11] can be made by four different methods; by two of these methods from water containing vitriol; by one method from a solution of _melanteria_, _sory_ and _chalcitis_; and by another method from earth or stones mixed with vitriol.

[Ill.u.s.tration 574 (Vitriol Making): A--Tunnel. B--Bucket. C--Pit.]

The vitriol water is collected into pools, and if it cannot be drained into them, it must be drawn up and carried to them in buckets by a workman. In hot regions or in summer, it is poured into out-of-door pits which have been dug to a certain depth, or else it is extracted from shafts by pumps and poured into launders, through which it flows into the pits, where it is condensed by the heat of the sun. In cold regions and in winter these vitriol waters are boiled down with equal parts of fresh water in rectangular leaden caldrons; then, when cold, the mixture is poured into vats or into tanks, which Pliny calls wooden fish-tanks. In these tanks light cross-beams are fixed to the upper part, so that they may be stationary, and from them hang ropes stretched with little stones; to these the contents of the thickened solutions congeal and adhere in transparent cubes or seeds of vitriol, like bunches of grapes.

[Ill.u.s.tration 575 (Vitriol Making): A--Caldron. B--Tank. C--Cross-bars.

D--Ropes. E--Little stones.]

By the third method vitriol is made out of _melanteria_ and _sory_. If the mines give an abundant supply of _melanteria_ and _sory_, it is better to reject the _chalcitis_, and especially the _misy_, for from these the vitriol is impure, particularly from the _misy_. These materials having been dug and thrown into the tanks, they are first dissolved with water; then, in order to recover the pyrites from which copper is not rarely smelted and which forms a sediment at the bottom of the tanks, the solution is transferred to other vats, which are nine feet wide and three feet deep. Twigs and wood which float on the surface are lifted out with a broom made of twigs, and afterward all the sediment settles at the bottom of this vat. The solution is poured into a rectangular leaden caldron eight feet long, three feet wide, and the same in depth. In this caldron it is boiled until it becomes thick and viscous, when it is poured into a launder, through which it runs into another leaden caldron of the same size as the one described before.

When cold, the solution is drawn off through twelve little launders, out of which it flows into as many wooden tubs four and a half feet deep and three feet wide. Upon these tubs are placed perforated crossbars distant from each other from four to six digits, and from the holes hang thin laths, which reach to the bottom, with pegs or wedges driven into them.

The vitriol adheres to these laths, and within the s.p.a.ce of a few days congeals into cubes, which are taken away and put into a chamber having a sloping board floor, so that the moisture which drips from the vitriol may flow into a tub beneath. This solution is re-boiled, as is also that solution which was left in the twelve tubs, for, by reason of its having become too thin and liquid, it did not congeal, and was thus not converted into vitriol.

[Ill.u.s.tration 576 (Vitriol Making): A--Wooden tub. B--Cross-bars.

C--Laths. D--Sloping floor of the chamber. E--Tub placed under it.]

[Ill.u.s.tration 577 (Vitriol Making): A--Caldron. B--Moulds. C--Cakes.]

The fourth method of making vitriol is from vitriolous earth or stones.

Such ore is at first carried and heaped up, and is then left for five or six months exposed to the rain of spring and autumn, to the heat of summer, and to the rime and frost of winter. It must be turned over several times with shovels, so that the part at the bottom may be brought to the top, and it is thus ventilated and cooled; by this means the earth crumbles up and loosens, and the stone changes from hard to soft. Then the ore is covered with a roof, or else it is taken away and placed under a roof, and remains in that place six, seven, or eight months. Afterward as large a portion as is required is thrown into a vat, which is half-filled with water; this vat is one hundred feet long, twenty-four feet wide, eight feet deep. It has an opening at the bottom, so that when it is opened the dregs of the ore from which the vitriol comes may be drawn off, and it has, at the height of one foot from the bottom, three or four little holes, so that, when closed, the water may be retained, and when opened the solution flows out. Thus the ore is mixed with water, stirred with poles and left in the tank until the earthy portions sink to the bottom and the water absorbs the juices.

Then the little holes are opened, the solution flows out of the vat, and is caught in a vat below it; this vat is of the same length as the other, but twelve feet wide and four feet deep. If the solution is not sufficiently vitriolous it is mixed with fresh ore; but if it contains enough vitriol, and yet has not exhausted all of the ore rich in vitriol, it is well to dissolve the ore again with fresh water. As soon as the solution becomes clear, it is poured into the rectangular leaden caldron through launders, and is boiled until the water is evaporated.

Afterward as many thin strips of iron as the nature of the solution requires, are thrown in, and then it is boiled again until it is thick enough, when cold, to congeal into vitriol. Then it is poured into tanks or vats, or any other receptacle, in which all of it that is apt to congeal does so within two or three days. The solution which does not congeal is either poured back into the caldron to be boiled again, or it is put aside for dissolving the new ore, for it is far preferable to fresh water. The solidified vitriol is hewn out, and having once more been thrown into the caldron, is re-heated until it liquefies; when liquid, it is poured into moulds that it may be made into cakes. If the solution first poured out is not satisfactorily thickened, it is condensed two or three times, and each time liquefied in the caldron and re-poured into the moulds, in which manner pure cakes, beautiful to look at, are made from it.

The vitriolous pyrites, which are to be numbered among the mixtures (_mistura_), are roasted as in the case of alum, and dissolved with water, and the solution is boiled in leaden caldrons until it condenses into vitriol. Both alum and vitriol are often made out of these, and it is no wonder, for these juices are cognate, and only differ in the one point,--that the former is less, the latter more, earthy. That pyrites which contains metal must be smelted in the furnace. In the same manner, from other mixtures of vitriolic and metalliferous material are made vitriol and metal. Indeed, if ores of vitriolous pyrites abound, the miners split small logs down the centre and cut them off in lengths as long as the drifts and tunnels are wide, in which they lay them down transversely; but, that they may be stable, they are laid on the ground with the wide side down and the round side up, and they touch each other at the bottom, but not at the top. The intermediate s.p.a.ce is filled with pyrites, and the same crushed are scattered over the wood, so that, coming in or going out, the road is flat and even. Since the drifts or tunnels drip with water, these pyrites are soaked, and from them are freed the vitriol and cognate things. If the water ceases to drip, these dry and harden, and then they are raised from the shafts, together with the pyrites not yet dissolved in the water, or they are carried out from the tunnels; then they are thrown into vats or tanks, and boiling water having been poured over them, the vitriol is freed and the pyrites are dissolved. This green solution is transferred to other vats or tanks, that it may be made clear and pure; it is then boiled in the lead caldrons until it thickens; afterward it is poured into wooden tubs, where it condenses on rods, or reeds, or twigs, into green vitriol.

Sulphur is made from sulphurous waters, from sulphurous ores, and from sulphurous mixtures. These waters are poured into the leaden caldrons and boiled until they condense into sulphur. From this latter, heated together with iron-scales, and transferred into pots, which are afterward covered with lute and refined sulphur, another sulphur is made, which we call _caballinum_.[12]

[Ill.u.s.tration 579 (Sulphur Making): A--Pots having spouts. B--Pots without spouts. C--Lids.]

The ores[13] which consist mostly of sulphur and of earth, and rarely of other minerals, are melted in big-bellied earthenware pots. The furnaces, which hold two of these pots, are divided into three parts; the lowest part is a foot high, and has an opening at the front for the draught; the top of this is covered with iron plates, which are perforated near the edges, and these support iron rods, upon which the firewood is placed. The middle part of the furnace is one and a half feet high, and has a mouth in front, so that the wood may be inserted; the top of this has rods, upon which the bottom of the pots stand. The upper part is about two feet high, and the pots are also two feet high and one digit thick; these have below their mouths a long, slender spout. In order that the mouth of the pot may be covered, an earthenware lid is made which fits into it. For every two of these pots there must be one pot of the same size and shape, and without a spout, but having three holes, two of which are below the mouth and receive the spouts of the two first pots; the third hole is on the opposite side at the bottom, and through it the sulphur flows out. In each furnace are placed two pots with spouts, and the furnace must be covered by plates of iron smeared over with lute two digits thick; it is thus entirely closed in, but for two or three vent-holes through which the mouths of the pots project. Outside of the furnace, against one side, is placed the pot without a spout, into the two holes of which the two spouts of the other pots penetrate, and this pot should be built in at both sides to keep it steady. When the sulphur ore has been placed in the pots, and these placed in the furnace, they are closely covered, and it is desirable to smear the joint over with lute, so that the sulphur will not exhale, and for the same reason the pot below is covered with a lid, which is also smeared with lute. The wood having been kindled, the ores are heated until the sulphur is exhaled, and the vapour, arising through the spout, penetrates into the lower pot and thickens into sulphur, which falls to the bottom like melted wax. It then flows out through the hole, which, as I said, is at the bottom of this pot; and the workman makes it into cakes, or thin sticks or thin pieces of wood are dipped in it. Then he takes the burning wood and glowing charcoal from the furnace, and when it has cooled, he opens the two pots, empties the residues, which, if the ores were composed of sulphur and earth, resemble naturally extinguished ashes; but if the ores consisted of sulphur and earth and stone, or sulphur and stone only, they resemble earth completely dried or stones well roasted. Afterward the pots are re-filled with ore, and the whole work is repeated.

[Ill.u.s.tration 581 (Sulphur Making): A--Long wall. B--High walls. C--Low walls. D--Plates. E--Upper pots. F--Lower pots.]

The sulphurous mixture, whether it consists of stone and sulphur only, or of stone and sulphur and metal, may be heated in similar pots, but with perforated bottoms. Before the furnace is constructed, against the "second" wall of the works two lateral part.i.tions are built seven feet high, three feet long, one and a half feet thick, and these are distant from each other twenty-seven feet. Between them are seven low brick walls, that measure but two feet and the same number of digits in height, and, like the other walls, are three feet long and one foot thick; these little walls are at equal distances from one another, consequently they will be two and one half feet apart. At the top, iron bars are fixed into them, which sustain iron plates three feet long and wide and one digit thick, so that they can bear not only the weight of the pots, but also the fierceness of the fire. These plates have in the middle a round hole one and a half digits wide; there must not be more than eight of these, and upon them as many pots are placed. These pots are perforated at the bottom, and the same number of whole pots are placed underneath them; the former contain the mixture, and are covered with lids; the latter contain water, and their mouths are under the holes in the plates. After wood has been arranged round the upper pots and ignited, the mixture being heated, red, yellow, or green sulphur drips from it and flows down through the hole, and is caught by the pots placed underneath the plates, and is at once cooled by the water. If the mixture contains metal, it is reserved for smelting, and, if not, it is thrown away. The sulphur from such a mixture can best be extracted if the upper pots are placed in a vaulted furnace, like those which I described among other metallurgical subjects in Book VIII., which has no floor, but a grate inside; under this the lower pots are placed in the same manner, but the plates must have larger holes.

[Ill.u.s.tration 582 (Bitumen Making): A--Lower pot. B--Upper pot. C--Lid.]

Others bury a pot in the ground, and place over it another pot with a hole at the bottom, in which pyrites or _cadmia_, or other sulphurous stones are so enclosed that the sulphur cannot exhale. A fierce fire heats the sulphur, and it drips away and flows down into the lower pot, which contains water. (Ill.u.s.tration p. 582).

[Ill.u.s.tration 583 (Bitumen Making): A--Bituminous spring. B--Bucket.

C--Pot. D--Lid.]

Bitumen[14] is made from bituminous waters, from liquid bitumen, and from mixtures of bituminous substances. The water, bituminous as well as salty, at Babylon, as Pliny writes, was taken from the wells to the salt works and heated by the great heat of the sun, and condensed partly into liquid bitumen and partly into salt. The bitumen being lighter, floats on the top, while the salt being heavier, sinks to the bottom.

Liquid bitumen, if there is much floating on springs, streams and rivers, is drawn up in buckets or other vessels; but, if there is little, it is collected with goose wings, pieces of linen, _ralla_, shreds of reeds, and other things to which it easily adheres, and it is boiled in large bra.s.s or iron pots by fire and condensed. As this bitumen is put to divers uses, some mix pitch with the liquid, others old cart-grease, in order to temper its viscosity; these, however long they are boiled in the pots, cannot be made hard. The mixtures containing bitumen are also treated in the same manner as those containing sulphur, in pots having a hole in the bottom, and it is rare that such bitumen is not highly esteemed.

[Ill.u.s.tration 585 (Chrysocolla Making): A--Mouth of the tunnel.

B--Trough. C--Tanks. D--Little trough.]

Since all solidified juices and earths, if abundantly and copiously mixed with the water, are deposited in the beds of springs, streams or rivers, and the stones therein are coated by them, they do not require the heat of the sun or fire to harden them. This having been pondered over by wise men, they discovered methods by which the remainder of these solidified juices and unusual earths can be collected. Such waters, whether flowing from springs or tunnels, are collected in many wooden tubs or tanks arranged in consecutive order, and deposit in them such juices or earths; these being sc.r.a.ped off every year, are collected, as _chrysocolla_[15] in the Carpathians and as ochre in the Harz.

There remains gla.s.s, the preparation of which belongs here, for the reason that it is obtained by the power of fire and subtle art from certain solidified juices and from coa.r.s.e or fine sand. It is transparent, as are certain solidified juices, gems, and stones; and can be melted like fusible stones and metals. First I must speak of the materials from which gla.s.s is made; then of the furnaces in which it is melted; then of the methods by which it is produced.

It is made from fusible stones and from solidified juices, or from other juicy substances which are connected by a natural relations.h.i.+p. Stones which are fusible, if they are white and translucent, are more excellent than the others, for which reason crystals take the first place. From these, when pounded, the most excellent transparent gla.s.s was made in India, with which no other could be compared, as Pliny relates. The second place is accorded to stones which, although not so hard as crystal, are yet just as white and transparent. The third is given to white stones, which are not transparent. It is necessary, however, first of all to heat all these, and afterward they are subjected to the pestle in order to break and crush them into coa.r.s.e sand, and then they are pa.s.sed through a sieve. If this kind of coa.r.s.e or fine sand is found by the gla.s.s-makers near the mouth of a river, it saves them much labour in burning and crus.h.i.+ng. As regards the solidified juices, the first place is given to soda; the second to white and translucent rock-salt; the third to salts which are made from lye, from the ashes of the musk ivy, or from other salty herbs. Yet there are some who give to this latter, and not to the former, the second place. One part of coa.r.s.e or fine sand made from fusible stones should be mixed with two parts of soda or of rock-salt or of herb salts, to which are added minute particles of _magnes_.[16] It is true that in our day, as much as in ancient times, there exists the belief in the singular power of the latter to attract to itself the vitreous liquid just as it does iron, and by attracting it to purify and transform green or yellow into white; and afterward fire consumes the _magnes_. When the said juices are not to be had, two parts of the ashes of oak or holmoak, or of hard oak or Turkey oak, or if these be not available, of beech or pine, are mixed with one part of coa.r.s.e or fine sand, and a small quant.i.ty of salt is added, made from salt water or sea-water, and a small particle of _magnes_; but these make a less white and translucent gla.s.s. The ashes should be made from old trees, of which the trunk at a height of six feet is hollowed out and fire is put in, and thus the whole tree is consumed and converted into ashes. This is done in winter when the snow lies long, or in summer when it does not rain, for the showers at other times of the year, by mixing the ashes with earth, render them impure; for this reason, at such times, these same trees are cut up into many pieces and burned under cover, and are thus converted into ashes.

[Ill.u.s.tration 587 (Gla.s.s-making Furnace): A--Lower chamber of the first furnace. B--Upper chamber. C--Vitreous ma.s.s.]

Some gla.s.s-makers use three furnaces, others two, others only one. Those who use three, melt the material in the first, re-melt it in the second, and in the third they cool the glowing gla.s.s vessels and other articles. Of these the first furnace must be vaulted and similar to an oven. In the upper chamber, which is six feet long, four feet wide, and two feet high, the mixed materials are heated by a fierce fire of dry wood until they melt and are converted into a vitreous ma.s.s. And if they are not satisfactorily purified from dross, they are taken out and cooled and broken into pieces; and the vitreous pieces are heated in pots in the same furnace.

[Ill.u.s.tration 588 (Gla.s.s-making Furnace): A--Arches of the second furnace. B--Mouth of the lower chamber. C--Windows of the upper chamber.

D--Big-bellied pots. E--Mouth of the third furnace. F--Recesses for the receptacles. G--Openings in the upper chamber. H--Oblong receptacles.]

The second furnace is round, ten feet in diameter and eight feet high, and on the outside, so that it may be stronger, it is encompa.s.sed by five arches, one and one half feet thick; it consists in like manner of two chambers, of which the lower one is vaulted and is one and one half feet thick. In front this chamber has a narrow mouth, through which the wood can be put into the hearth, which is on the ground. At the top and in the middle of its vault, there is a large round hole which opens to the upper chamber, so that the flames can penetrate into it. Between the arches in the walls of the upper chamber are eight windows, so large that the big-bellied pots may be placed through them on to the floor of the chamber, around the large hole. The thickness of these pots is about two digits, their height the same number of feet, and the diameter of the belly one and a half feet, and of the mouth and bottom one foot. In the back part of the furnace is a rectangular hole, measuring in height and width a palm, through which the heat penetrates into a third furnace which adjoins it.

This third furnace is rectangular, eight feet long and six feet wide; it also consists of two chambers, of which the lower has a mouth in front, so that firewood may be placed on the hearth which is on the ground. On each side of this opening in the wall of the lower chamber is a recess for oblong earthenware receptacles, which are about four feet long, two feet high, and one and a half feet wide. The upper chamber has two holes, one on the right side, the other on the left, of such height and width that earthenware receptacles may be conveniently placed in them.

These latter receptacles are three feet long, one and a half feet high, the lower part one foot wide, and the upper part rounded. In these receptacles the gla.s.s articles, which have been blown, are placed so that they may cool in a milder temperature; if they were not cooled slowly they would burst asunder. When the vessels are taken from the upper chamber, they are immediately placed in the receptacles to cool.

[Ill.u.s.tration 589 (Gla.s.s-making Furnaces): A--Lower chamber of the other second furnace. B--Middle one. C--Upper one. D--Its opening.

E--Round opening. F--Rectangular opening.]

Some who use two furnaces partly melt the mixture in the first, and not only re-melt it in the second, but also replace the gla.s.s articles there. Others partly melt and re-melt the material in different chambers of the second furnace. Thus the former lack the third furnace, and the latter, the first. But this kind of second furnace differs from the other second furnace, for it is, indeed, round, but the interior is eight feet in diameter and twelve feet high, and it consists of three chambers, of which the lowest is not unlike the lowest of the other second furnace. In the middle chamber wall there are six arched openings, in which are placed the pots to be heated, and the remainder of the small windows are blocked up with lute. In the middle top of the middle chamber is a square opening a palm in length and width. Through this the heat penetrates into the upper chamber, of which the rear part has an opening to receive the oblong earthenware receptacles, in which are placed the gla.s.s articles to be slowly cooled. On this side, the ground of the workshop is higher, or else a bench is placed there, so that the gla.s.s-makers may stand upon it to stow away their products more conveniently.

Those who lack the first furnace in the evening, when they have accomplished their day's work, place the material in the pots, so that the heat during the night may melt it and turn it into gla.s.s. Two boys alternately, during night and day, keep up the fire by throwing dry wood on to the hearth. Those who have but one furnace use the second sort, made with three chambers. Then in the evening they pour the material into the pots, and in the morning, having extracted the fused material, they make the gla.s.s objects, which they place in the upper chamber, as do the others.

The second furnace consists either of two or three chambers, the first of which is made of unburnt bricks dried in the sun. These bricks are made of a kind of clay that cannot be easily melted by fire nor resolved into powder; this clay is cleaned of small stones and beaten with rods.

The bricks are laid with the same kind of clay instead of lime. From the same clay the potters also make their vessels and pots, which they dry in the shade. These two parts having been completed, there remains the third.

[Ill.u.s.tration 591 (Gla.s.s Making): A--Blow-pipe. B--Little window.

C--Marble. D--Forceps. E--Moulds by means of which the shapes are produced.]

The vitreous ma.s.s having been made in the first furnace in the manner I described, is broken up, and the a.s.sistant heats the second furnace, in order that the fragments may be re-melted. In the meantime, while they are doing this, the pots are first warmed by a slow fire in the first furnace, so that the vapours may evaporate, and then by a fiercer fire, so that they become red in drying. Afterward the gla.s.s-makers open the mouth of the furnace, and, seizing the pots with tongs, if they have not cracked and fallen to pieces, quickly place them in the second furnace, and they fill them up with the fragments of the heated vitreous ma.s.s or with gla.s.s. Afterward they close up all the windows with lute and bricks, with the exception that in each there are two little windows left free; through one of these they inspect the gla.s.s contained in the pot, and take it up by means of a blow-pipe; in the other they rest another blow-pipe, so that it may get warm. Whether it is made of bra.s.s, bronze, or iron, the blow-pipe must be three feet long. In front of the window is inserted a lip of marble, on which rests the heaped-up clay and the iron s.h.i.+eld. The clay holds the blow-pipe when it is put into the furnace, whereas the s.h.i.+eld preserves the eyes of the gla.s.s-maker from the fire. All this having been carried out in order, the gla.s.s-makers bring the work to completion. The broken pieces they re-melt with dry wood, which emits no smoke, but only a flame. The longer they re-melt it, the purer and more transparent it becomes, the fewer spots and blisters there are, and therefore the gla.s.s-makers can carry out their work more easily. For this reason those who only melt the material from which gla.s.s is made for one night, and then immediately make it up into gla.s.s articles, make them less pure and transparent than those who first produce a vitreous ma.s.s and then re-melt the broken pieces again for a day and a night. And, again, these make a less pure and transparent gla.s.s than do those who melt it again for two days and two nights, for the excellence of the gla.s.s does not consist solely in the material from which it is made, but also in the melting. The gla.s.s-makers often test the gla.s.s by drawing it up with the blowpipes; as soon as they observe that the fragments have been re-melted and purified satisfactorily, each of them with another blow-pipe which is in the pot, slowly stirs and takes up the gla.s.s which sticks to it in the shape of a ball like a glutinous, coagulated gum. He takes up just as much as he needs to complete the article he wishes to make; then he presses it against the lip of marble and kneads it round and round until it consolidates. When he blows through the pipe he blows as he would if inflating a bubble; he blows into the blow-pipe as often as it is necessary, removing it from his mouth to re-fill his cheeks, so that his breath does not draw the flames into his mouth. Then, twisting the lifted blow-pipe round his head in a circle, he makes a long gla.s.s, or moulds the same in a hollow copper mould, turning it round and round, then warming it again, blowing it and pressing it, he widens it into the shape of a cup or vessel, or of any other object he has in mind. Then he again presses this against the marble to flatten the bottom, which he moulds in the interior with his other blow-pipe. Afterward he cuts out the lip with shears, and, if necessary, adds feet and handles. If it so please him, he gilds it and paints it with various colours. Finally, he lays it in the oblong earthenware receptacle, which is placed in the third furnace, or in the upper chamber of the second furnace, that it may cool. When this receptacle is full of other slowly-cooled articles, he pa.s.ses a wide iron bar under it, and, carrying it on the left arm, places it in another recess.

The gla.s.s-makers make divers things, such as goblets, cups, ewers, flasks, dishes, plates, panes of gla.s.s, animals, trees, and s.h.i.+ps, all of which excellent and wonderful works I have seen when I spent two whole years in Venice some time ago. Especially at the time of the Feast of the Ascension they were on sale at Morano, where are located the most celebrated gla.s.s-works. These I saw on other occasions, and when, for a certain reason, I visited Andrea Naugerio in his house which he had there, and conversed with him and Francisco Asulano.

END OF BOOK XII.

FOOTNOTES:

[1] The history of salt-making in salt-pans, from sea-water or salt springs, goes further back than human records. From an historical point of view the real interest attached to salt lies in the bearing which localities rich in either natural salt or salt springs, have had upon the movements of the human race. Many ancient trade routes have been due to them, and innumerable battles have been fought for their possession.

Salt has at times served for currency, and during many centuries in nearly every country has served as a basis of taxation. These subjects do not, however, come within the scope of this text. For the quotation from Pliny referred to, see Note 14 below, on bitumen.

[2] The first edition gives _graviorem_, the latter editions _gratiorem_, which latter would have quite the reverse meaning from the above.

[3] The following are approximately the English equivalents:--