In our day stone of this sort is never wrought to perfection,[[15]] because our artificers have lost the art of tempering the chisels and other instruments for working them. It is true that they can still, with the help of emery, saw drums of columns into slices, and cut other pieces to be arranged in patterns for floors, and make various other ornaments for buildings. The porphyry is reduced little by little by means of a copper saw, without teeth, drawn backwards and forwards between two men, which, with the aid of emery reduced to powder, and kept constantly wet with water, finally cuts its way through the stone.[[16]] Although at different times many ingenious attempts have been made to find out the method of working porphyry used by the ancients,[[17]] all have been in vain, and Leon Battista Alberti, the first to make experiments therein not however in things of great moment, did not find, among the many tempering-baths that he put to the test, any that answered better than goats’ blood; because, though in the working it removed but little of that hardest of stones and was always striking sparks of fire, it served him nevertheless so far as to enable him to have carved, in the threshold of the principal door of Santa Maria Novella in Florence, the eighteen antique letters, very large and well proportioned, which are seen on the front of the step, in a piece of porphyry. These letters form the words Bernardo Oricellario.[[18]] And because the edge of the chisel did not suit for squaring the corners, or giving the necessary polish and finish, he had a little revolving drill made, with a handle like a spit, which was easily worked by placing the said handle against the chest, and putting the hands into the crank in order to turn it.[[19]] At the working end, instead of a chisel or bit, he fixed copper discs, larger or smaller according to need, and these, well sprinkled with emery, gradually reduced and smoothed the stone, producing a fine surface and finishing the corners, the drill all the while being dexterously twirled by the hand. But all this effort cost so much time, that Leon Battista lost heart, and did not put his hand to anything else, either in the way of statues, or vases, or other delicate work. Others, afterwards, who set themselves to smoothing stones and restoring columns by the same special process, have done it in this way. They make for the purpose large and heavy hammers, with the points of steel, keenly tempered with goats’ blood, and worked in the manner of diamond points; with these they carefully tap on the porphyry, and ‘scabbling’ it, or working it down, little by little the best way they can, finally reduce it, with much time and trouble, to the round or the flat, as the workman chooses,—not however to the form of statues, because of this we have lost the art—and they polish it with emery and leather, scouring it till there comes a lustre very clear and well finished.
Fig. 1.—Inscribed Porphyry Tablet at Santa Maria Novella, Florence.
Now although every day refinements are being made on human inventions, and new things enquired into, yet even the moderns, who from time to time have tried fresh methods of carving porphyry, various tempering-baths, and very carefully refined steels, have, as was said above, up till recent years laboured in vain. Thus in the year 1553 Pope Julius III, having been presented by Signor Ascanio Colonna[[20]] with a very handsome antique porphyry basin, measuring seven braccia across, ordered it to be restored, for some pieces were missing, that it might adorn his vineyard: the work was undertaken, and many things tried by the advice of Michelagnolo Buonarroti and of other excellent masters, but after a great length of time the enterprise was despaired of, chiefly because it was found impossible to preserve some of the arrises, a matter essential to the undertaking: Michelagnolo, moreover, even though accustomed to the hardness of stones, gave up the attempt, as did all the others, and nothing more was done.
Plate II
PRINCIPAL DOORWAY AT S. MARIA NOVELLA, FLORENCE
Showing the position of the inscribed porphyry tablet on the riser or the step
At last, since no other thing in our days was lacking to the perfection of our arts, except the method of satisfactorily working porphyry, that not even this should still be to seek, it was rediscovered in the following manner. In the year 1555, Duke Cosimo, wishing to erect a fountain of remarkable beauty in the court of his principal palace in Florence, had excellent water led there from the Pitti Palace and Garden, and ordered a basin with its pedestal to be made for the said fountain from some large pieces of porphyry found among broken fragments. To make the working of it more easy to the master, he caused an extract to be distilled from an herb, the name of which is unknown to me, and this extract had such virtue, that red-hot tools when plunged into it acquired the hardest possible temper. With the aid of this process then, Francesco del Tadda, the carver of Fiesole,[[21]] executed after my design the basin of the said fountain, which is two and a half braccia in diameter,[[22]] together with its pedestal, just as it may be seen to-day in the above-named palace.[[23]] Tadda, judging that the secret imparted to him by the duke was very precious, set himself to put it to the test by carving something, and he has succeeded so well that in a short time he has made, in three ovals, life-size portraits in half relief of Duke Cosimo and of the duchess Leonora, and a head of Christ, executed so perfectly that the hair and beard, most difficult to reproduce in carving, are finished in a manner equal to that of the ancients. The Duke was talking one day of these works with Michelagnolo[[24]] when his Excellency was in Rome, and Buonarroti would not believe in them; therefore, by the Duke’s order, I sent the head of Christ to Rome where it was seen by Michelagnolo with great wonder, who praised it highly and rejoiced greatly to see the sculpture of our time enriched by this rare gift, which until our day had been searched for in vain. Tadda has recently finished the head of the elder Cosimo de’ Medici[[25]] in an oval, like those mentioned above, and he has executed and continues to execute many other similar works.
All that remains to be said of porphyry is that, because the quarries are now lost to knowledge,[[26]] it is necessary to make use of what is left of it in the form of ancient fragments, drums of columns and other pieces; and that in consequence he who works in porphyry must ascertain whether or not it has been subjected to the action of fire, because if it have, although it does not completely lose its colour, nor crumble away, it lacks much of its natural vividness and never takes so good a polish as when it has not been so subjected; and, what is worse, it easily fractures in the working. It is also worth knowing, as regards the nature of porphyry, that, if put into the furnace, it does not burn away (non si cuoce),[[27]] nor allow other stones round it to be thoroughly burnt; indeed, as to itself, it grows raw (incrudelisce) as is shown in the two columns the men of Pisa gave to the Florentines in the year 1117 after the acquisition of Majorca. These columns now stand at the principal door of the church of San Giovanni; they are colourless and not very well polished in consequence of having passed through fire, as Giovanni Villani relates in his history.[[28]]
Plate III
PORTRAIT IN PORPHYRY OF COSIMO ‘PATER PATRIAE’
BY FRANCESCO DEL TADDA