FOOTNOTES:
[216] Stagnuolo, i.e., tinfoil.
[217] Forza.
[218] E finito magro in circa un dito.
[219] L’anima, or internal block.
[220] E da basso in sino alla metà dei talloni.
[221] Camicia.
[222] Torce.
[223] Che viene a essere quella prima camicia.
[224] Or ‘mother mould’ as the sculptors would call it.
[225] Succhiellino di tutti quei pezzi che ti tenevano i sotto squadri.
[226] Da poi che tu arai vestito tutta la tua camicia.
[227] Page 113.
[228] Succhielletto.
[229] E di poi che tu ti sei resoluto.
[230] Tonaca.
[231] Loti.
[232] Dinanzi alla spina.
[233] Bocca.
[234] Anima.
[235] Spoglia.
[236] Spine.
[237] Mazzapicchi.
[238] Via.
[239] Bocca principale.
[240] Bocca della spina, i.e., the egress channel.
[241] Con tutto ci sia poco differenzia.
[242] Accomodandoli intorno al tuo canale tanto quanto viene alto.
[243] E rinfrescala con una certa quantita di stagno di piu della lega ordinaria, la quale vuole essere circa una mezza libbra per cento di piu della lega che vi arai messa. Professor Roberts-Austen is of opinion that this implies an additional half-pound of pewter for every 100 lbs. of bronze you have in the furnace. If it is not so, should the word ‘pewter’ be translated ‘tin’? that is the lead-tin alloy should contain half-pound more tin (than is usual) in every 100 lbs.
[244] I rastiatoi. Brinckman has ‘kratzeisen.’
[245] Maestri d’artiglierie. See above.
[246] See the account of this in the ‘Vita,’ p. 420 and onwards.
[247] Condotto il mio bronzo in bagno.
[248] Stata a disagio ei s’e fatto un migliaccio.
[249] Una cosa la quale usciva di quella ordinaria praticaccia.
[250] Un morto: our workshop slang of the ‘dead horse’ would seem to meet Cellini’s meaning here.
[251] Una continova pratica.
[252] Nocciolo.
[253] Di poi sciolto il suo cavo.
[254] Tonaca.
CHAPTER IV. HOW TO CONSTRUCT FURNACES FOR CASTING BRONZE, WHETHER FOR STATUES, ORDNANCE, OR OTHER SUCH-LIKE THINGS.
Furnaces for casting bronze have to be made by each master according as the special needs of his piece of work require it. Inasmuch as at the beginning of my book I promised always to illustrate what I was describing by work of my own, I will do so with furnaces also. When working for good King Francis, I had to make a great bronze gate, for which a special furnace had to be constructed. This I did in my own castle, given to me in royal letters patent by his Majesty, whom I served most loyally for four years; and these letters patent I brought back with me to Florence, if only to show in Italy & my native land what great treasures may not be acquired, and how good it is after having been trained in Italy to leave home, and reap such useful & honourable fruits abroad.
Well, then, having to make a furnace, this was the way I did it. The hollow within was three Florentine cubits wide, which made it about nine cubits in circumference, the height of the vault of the furnace was equal in size and shape to the half circle of the bed.[255] To this bed, most gentle reader, I want you to give special attention; I do not intend making a drawing of it, because I have seen so many architectural drawings altered and spoiled, so I shall content myself with words only to convey what I mean, and such as I trust may suffice. [256] In a furnace of this nature, the bed, i.e. the place where the metal is put, must be constructed with a fall, just as I made the little one in question. The total fall to the bottom of the bed should be about one-sixth of a cubit, and see that it is shaped in the manner of the streets you go a-walking in that have in the middle of them what in Tuscany we call a rigaguolo or gulley; this gulley runs direct to the mouth of the outlet hole out of which the metal is to flow. The shoulders[257] of the gulley should slope up ever so gently, till they come to within about one-third of a cubit at the two gates[258] where you put the bronze. This third you can increase or not by one-sixteenth of a cubit according to whether you wish to increase or decrease the depth of your furnace. The third door, about which you need not be so particular, is the one through which the fire enters, &, as it is not brought into direct connection with the bronze, it need only be blocked with a little mound of earth about three fingers high. The bed of your furnace should be of bricks, specially constructed, they should be small, but bigger at one end than the other, & measuring one-sixth of a cubit in either direction; by far the best are those used for glass furnaces, which are made much in the same way as other bricks. Some have shaped their bricks with a cutting instrument[259] as they went along, but I find, after having tried one way & another, that the best results can be obtained by having them all the same size. Care should be taken to make the bricks of a clay that does not yield in the fire; in my native city of Florence we use a kind of white clay, said to come from Monte Carlo, and all our glass furnaces were constructed with it. In France I found another and ever so much better way. The bricks are one-fourth of a cubit long, & the same width as the above, they call them ciment, and they make them out of crucibles used in founderies, of which there are no end in those parts. But your master has got to accommodate himself to the conditions of workmanship in every place he works in. When your bricks are thus made, they must when quite dry, be carefully worked over with iron tools, somewhat in the nature of axes or large chisels made specially for the purpose, so as to make them cohere as well as possible. After this they are gradually cemented with quarry stones[260] to the thickness of about half a cubit, so that you get an absolutely firm floor for your furnace. These quarry stones should be at least one-third of a cubit in size, and ever so firmly united. The first or lower part of a furnace of this description should be, in diameter two-thirds of a cubit larger than the upper portion. Both must be walled with ordinary lime, provided it be good, and after the lower, you proceed to wall the upper, the portion in which the bronze has to be placed.
Having fashioned your bricks out of the fire-resisting earth just referred to, you take some of this earth, and make a paste of it as you would of lime, minding however, that it is well sifted and clean, and with it wall the whole base of your furnace. I insist again upon the need of your working over the bricks with your chisels carefully, & smoothing them well, so that they fit together absolutely, and in thus fitting them, you must make the jointings as thin as possible. Sometimes it happens, owing to some little negligence on the master’s part, if he mix the liquid earth too coarsely, that the tiniest little cracks form in the drying. These cracks, however small they be, are mighty dangerous, & may cause incalculable mischief; for, when the bronze grows liquid, such is its terrific force, that it penetrates into them, be they never so small, and I myself have seen the whole thing burst up owing to this.[261] But when due care is observed, & the walling made with the finest possible liquid earth, there is no need for cracks, your bronze may be safely melted, and all your work come scatheless from the furnace.
After the bed you build up the vault with similar bricks in the same way, in doing which you must remember, as I said before, to make your two openings for putting in the bronze; two-thirds of a cubit wide and three-quarters of a cubit high will suffice them, and they must be semi-circular atop. There must also be a third opening two-thirds of a cubit wide and one cubit high for the fire to enter in at, so that the flame, as is its wont, may curl powerfully to the top of the vault, and thence curl down again, [262] and with great heat play upon the metal, & melt it rapidly. Four air vents have to be distributed round the spring of the top of the furnace vault.[263]
In one of the vault bricks, at the lower end of the channel, a mouth must be made much like the air vents, & big enough for you to put in two fingers quite comfortably. The air vent too must be the same size. This mouth, out of which the bronze is to flow, must be made from one brick; & mind that it is a good sound one. The said brick, too, must, moreover, be built into its place just as the others were, and helping with them to gradually lock in the vault at the top. So that you don’t think me inaccurate, I would have you know that this mouth is called bocca della spina, the mouth of the plug; it must be half a finger wider inside than out, and before you pour out the metal you keep it stopped with an iron stopper luted with a little ash made into a kind of paste. Then you take a quarry stone about half a cubit square & make a hole through the middle of it. This hole is to be exactly the size of the mouth just made in the brick, that is to say on the side adjoining the brick, but on the other side, the side away from the furnace, it is to be six times as big, and it should be cleaned off[264] outside. Then you join it to the brickwork wall of the furnace with the earth, & in the manner mentioned above; but because the base and sides of the furnace have also to be considered, as I said before, you cement these with good ordinary lime. Similarly all the quarry stones must be the same size as the first piece, and be attached to the walling in the same manner, & they must be carried up to the height of the vault, but straight; so that in the event of any accident happening to the vault, for to that the craft is often liable, it may be mended or put in order. When you have walled your furnace round in this way you must be careful to join at the shoulders [265] of the principal orifice, by which the flame enters, [266] a hearth two-thirds of a cubit square & two cubits deep, measured from the bottom of this hole of the hearth. In this cavity you put six or seven iron bars, these are about two fingers thick, & of such length as to project beyond the sides of the hole about four fingers each way, and they rest upon pins set at intervals of about three fingers apart. This hearth made over the fire bars is constructed in just the same way, & with just the same bricks, and cemented with just the same mortar as was the furnace; it must stand from the ground to about the middle of the hole where the fire enters the fire bridge, and the part above this point must be narrowed to one-eighth of a cubit. Straight through this hole the wood is put. Under the grating a trench must be dug, & five or six cubits long, in the direction in which the draught is to pass through the grating into the hearth. Care must be taken that the draught only blows in one way, and that long-ways. We craftsmen call this trench bracciaiuola, the ash-pit, because all the ashes fall into it. How long the fire is to be kept up must be a matter of judgment; sometimes the master may have, owing to work he has to do on his mould, to keep it up for quite four or six hours. When the wood logs are burnt through, they fall into a great pile below the grating. And sometimes they heap up in such a way as to obstruct the force of the draught through the hearth, that it cannot do its work; heed must be taken then, that when the pile begins to grow big, the ashes must be raked asunder from time to time. To do this, you must have what we call a rastrello or rake, which you make as follows. You take a piece of iron half a cubit long and one-eighth of a cubit thick; on to the middle of this piece and at the upper and thicker side of it you weld an iron rod two fingers thick and two cubits long, at the other end of this is fashioned a ferule,[267] into which is fitted a wooden handle at least four cubits long.
Take heed, too, that when your whole furnace is duly made as above directed, you gird it round with two stout iron bands, the one round near the base, the other about one-third of a cubit higher up; the thicker and stouter these hoops are, the better, for I know by the experience of the casting of my Perseus how terrific the might of the fire is. The opening of the hearth through which the wood is put must be kept closed. The covering must be made in the form of an iron spade, of such a size as shall well cover the opening, and to this spade a handle of such convenient length that when, now and again, you have to manipulate it for putting on fresh wood or otherwise, you don’t burn yourself. It stands to reason that before all these things are accomplished, the metal has already been put in the furnace, & it must be stacked up in such a manner as to admit of flames playing easily through it, for this will make the working of your furnace much more effective.
Know, too, gentle reader, what up to now I have forgotten to tell you, that when with due care your furnace is made, you must, before putting the metal into it, heat it well through for a space of twenty-four hours; for if you do not do this, you will not get the metal to melt, nay rather will it stiffen, [268] and certain fumes will result from the damp earth that will so impede your work that it may be eight days before your metal begins to flow. That is what happened to me in Paris. I had made a little furnace and had put my trust in a very excellent old fellow, quite the best of his craft and about eighty years of age; but he hadn’t dried the furnace properly, and, sure enough, just as it was on the point of melting, & the fire at its fiercest, out came these earth fumes. When the old worthy saw that for all his heeding the metal was stiffening, he got into such a stew, the poor old chap, that what with his mighty exertions to overcome the difficulty, he fell flat down, and I took him for certain dead. Howbeit I had a great beaker of the choicest wine brought him, & since there was no such great risk in leaving the work as there was in the case of my Perseus; since, too, I served that most admirable of kings, and thus had not to bother so much about the peddling trivialities of making it pay, for however big it was it never mattered with him—I mixed a large bumper of wine for the old man, who was groaning away like anything, and I bade him most winning-wise to drink, & I stretched out my hand to him and said: ‘Drink, my father, for in yonder furnace has entered in a devil, who is making all the mischief, and, look you, we’ll just let him bide there a couple of days, till he gets jolly well bored, and then will we, you and I together, in the space of a three hours’ firing make this metal run like so much butter, & without any exertion at all.’ The old fellow drank, & then I brought him some little dainties to eat, meat pasties they were, nicely peppered, and I made him take down four full goblets of wine. He was a man quite out of the ordinary, this, and a most lovable old thing, and what with my caresses and the virtue of the wine, I found him soon moaning away as much with joy as he had moaned before with grief. When the appointed day came the fumes had duly evaporated, the furnace was quite ready and well heated, & in two hours we cast 1500 lbs. of metal, with which I finished certain portions that were left of my lunette of Fontainebleau. And that is why I insist upon your well heating the furnace, and also upon making two little quarry stone doors[269] at the furnace openings, and you make in each of them two holes one and a half fingers wide respectively, and four fingers apart from each other, and these holes serve for the insertion of an iron fork made specially to fit into them, with which now and again, as need occurs, you may open & shut the doors.
Remember, too, that each time new metal is to be put into the furnace it must be first put up against the doors[270] till it becomes red hot, for if you put it in too soon with the other metal already in, you run the risk of cooling the latter, & so caking it, [271] much as before referred to. Hence the very greatest care must be taken on that point.
In Paris have I seen craftsmen cast the most wonderful things imaginable, and also make equally wonderful blunders. And this is due to the fact that technical skill [272] serves you up to a certain point, but in some accident, for instance, you need the deeper knowledge of the principles of the art that leaves technical skill on one side, as I have evidenced to you above.
Indeed I may add that I have seen 100,000 lbs. of metal cast at one time with so much ease that I marvelled at it, so great was the technical skill with which it was done; at another time I saw a little error made that might easily have been remedied. I stood & watched whether they knew how to put it right, and I saw them throw it up, work and all, and so lose hundreds of scudi. Willingly would I have shown them what the remedy was, but their presumption was so huge that had they not known how to put my remedy into practice, they would have been quite capable of saying that I myself was the cause of all the ruin. So I stood mum and grew wise at their cost.
Gentle reader, let that suffice about furnaces and bronze casting, and let us now turn to other branches of the art.
[It is interesting to note that Biringoccio, a professed metallurgist, and a contemporary of Cellini, describing the reverberatory furnace (reverbero) in his celebrated metallurgical treatise ‘della Pirotechnica,’ 1540 (see above, [p. 106]), the first accurate treatise of its kind, gives fewer details than Cellini; he gives, however, diagrams which are very precious. Cellini’s decision not to give diagrams is much to be regretted. Biringoccio has, however, the following among other drawings of reverberatories. It serves to show what Cellini’s furnaces would have been in sectional plan. The letters are mine. It will be observed that no chimney is shown.]
Biringoccio’s Furnace from the ‘Pirotechnica’
a. Fire bars with ash pit under.
b. Furnace bed.
c. Fire door.
d. Fire bridge.