Travertine is excellent for walls, because after it is built up in squared courses and worked into mouldings, it can be entirely covered with stucco[[85]] and thereafter be impressed with any designs in relief that are desired, just as the ancients did in the public entrances to the Colosseum[[86]] and in many other places; and as Antonio da San Gallo has done in the present day in the hall of the Pope’s palace, in front of the chapel,[[87]] where he has faced the travertine with stucco bearing many excellent devices. More than any other master however has Michelagnolo Buonarroti ennobled this stone in the decoration of the court of the Casa Farnese.[[88]] With marvellous judgement he has used it for windows, masks, brackets, and many other such fancies; all these are worked as marble is worked and no other similar ornament can be seen to excel this in beauty. And if these things are rare, more wonderful than all is the great cornice on the front façade of the same palace, than which nothing more magnificent or more beautiful can be sought for. Michelagnolo has also employed travertine for certain large chapels on the outside of the building of St. Peter’s, and in the interior, for the cornice that runs all round the tribune; so finished is this cornice that not one of the joints can be perceived, everyone therefore can well understand with what advantage to the work we employ this kind of stone. But that which surpasses every other marvel is the construction in this stone of the vault of one of the three tribunes in St. Peter’s; the pieces composing it are joined in such a manner that not only is the building well tied together with various sorts of bonds, but looked at from the ground it appears made out of a single piece.[[89]]
§ 13. Of Slates.
We now come to a different order of stones, blackish in colour and used by the architects only for laying on roofs. These are thin flags produced by nature and time near the surface of the earth for the service of man. Some of these are made into receptacles, built up together in such a manner that the pieces dovetail one into the other. The vessels are filled with oil according to their holding capacity and they preserve it most thoroughly. These slates are a product of the sea coast of Genoa, in a place called Lavagna;[[90]] they are excavated in pieces ten braccia long and are made use of by artists for their oil paintings, because pictures painted on slate last much longer than on any other material, as we shall discuss more appropriately in the chapters on painting.
§ 14. Of Peperino.[[91]]
We shall also refer in a future chapter to a stone named piperno or more commonly peperigno, a blackish and spongy stone, resembling travertine, which is excavated in the Roman Campagna. It is used for the posts of windows and doors in various places, notably at Naples and in Rome; and it also serves artists for painting on in oil, as we shall relate in the proper place. This is a very thirsty stone and indeed more like cinder than anything else.
§ 15. Of the Stone from Istria.[[92]]
There is moreover quarried in Istria a stone of a livid white, which very easily splits, and this is more frequently used than any other, not by the city of Venice alone, but by all the province of Romagna, for all works both of masonry and carving. It is worked with tools and instruments longer than those usually employed, and chiefly with certain little hammers that follow the cleavage of the stone, where it readily parts. A great quantity of this kind of stone was used by Messer Jacopo Sansovino, who built the Doric edifice of the Panattiera[[93]] in Venice, and also that in the Tuscan style for the Zecca (mint) on the Piazza of San Marco.[[94]] Thus they go on executing all their works for that city, doors, windows, chapels, and any other decorations that they find convenient to make, notwithstanding the fact that breccias and other kinds of stone could easily be conveyed from Verona, by means of the river Adige. Very few works made of these latter materials are to be seen, because of the general use of the Istrian stone, into which porphyry, serpentine and other sorts of breccias are often inlaid, resulting in compositions which are very ornamental. This stone is of the nature of the limestone called ‘alberese,’ not unlike that of our own districts, and as has been said it splits easily.
§ 16. Of Pietra Serena.
There only remains now the pietra serena and the grey stone called ‘macigno’[[95]] and the pietra forte which is much used in the mountainous parts of Italy, especially in Tuscany, and most of all in Florence and her territory. The stone that they call pietra serena[[96]] draws towards blue or rather towards a greyish tint. There are quarries of it in many places near Arezzo, at Cortona, at Volterra, and throughout the Apennines. The finest is in the hills of Fiesole, and it is obtained there in blocks of very great size, as we see in all the edifices constructed in Florence by Filippo di Ser Brunellesco, who had all the stones needed for the churches of San Lorenzo and of Santo Spirito quarried there, and also an unlimited quantity which are in every building throughout the city. It is a very beautiful stone to look at, but it wastes away and exfoliates where it is subjected to damp, rain, or frost. Under cover however it will last for ever. Much more durable than this and of finer colour is a sort of bluish stone, in our day called ‘pietra del fossato.’[[97]] When quarried, the first layer is gravelly and coarse, the second is never free from knots and fissures, the third is admirable being much finer in grain. Michelagnolo used this, because of its yielding grain, in building the Library and Sacristy of San Lorenzo for Pope Clement, and he has had the mouldings, columns, and every part of the work executed with such great care that even if it were of silver it would not look so well.[[98]] The stone takes on a very fine polish, so much so that nothing better in this kind of material could be wished for. On this account it was forbidden by law that the stone be used in Florence for other than public buildings, unless permission had been obtained from the governing authorities.[[99]] The Duke Cosimo has had a great quantity of this stone put into use, as for example, in the columns and ornaments of the loggia of the Mercato Nuovo, and for the work begun by Bandinello in the great audience chamber of the palace and also in the other hall which is opposite to it; but the greatest amount, more than ever used elsewhere, has been taken by his Excellency for the Strada de’ Magistrati,[[100]] now in construction, after the design and under the direction of Giorgio Vasari of Arezzo. This stone demands as much time for working it as marble. It is so hard that water does not affect it and it withstands all other attacks of time.
Besides this there is another sort called pietra serena, found all over the hill, which is coarser, harder, and not so much coloured, and contains certain knots in the stone. It resists the influence of water and frost, and is useful for figures and carved ornaments. Of this is carved La Dovizia (Abundance), a figure from the hand of Donatello on the column of the Mercato Vecchio in Florence;[[101]] and it serves also for many other statues executed by excellent sculptors, not only in this city, but throughout the territory.