Now, by order of Pope Julius II, a commission was given to Bramante da Urbino to have a number of glass windows made for the Palace; whereupon he, making inquiries about the most excellent craftsmen, received information of many who were working at that craft, and among them of some who were executing marvellous works in France; and of these he saw a specimen through the French Ambassador who was then at the Court of his Holiness, and who had in the frame of a window in his study a figure executed on a piece of white glass with a vast number of colours, fixed on the glass by the action of fire. Wherefore, by order of Bramante, a letter was written to France, inviting them to come to Rome, and offering them good payments. Thereupon Maestro Claudio, a Frenchman, the head of that art, having received the intelligence, and knowing the excellence of Guglielmo, so went to work with money and fair promises, that it was no difficult matter to draw him out of the convent, particularly because Guglielmo, on account of the discourtesy shown to him and the jealousies that there always are among monks, was even more eager to leave it than was Maestro Claudio to get him out. They went, therefore, to Rome, where the habit of S. Dominic was changed for that of S. Peter.
Bramante at that time had caused two windows of travertine to be made in the Palace of the Pope, which were in the hall in front of the chapel, now embellished by a vaulted ceiling by Antonio da San Gallo, and by marvellous stucco-work from the hand of Perino del Vaga of Florence. These windows were executed by Maestro Claudio and Guglielmo, although afterwards, during the sack of Rome, they were broken to pieces, in order to extract the lead to make harquebus-balls; and they were truly marvellous. In addition to these, they made an endless number of them for the apartments of the Pope, which met with the same fate as the other two. And even now there is one to be seen in the room containing Raffaello's Burning of the Borgo, in the Borgia Tower; in which are angels who are holding the escutcheon of Leo X. They also made two windows for the chapel behind the Madonna in S. Maria del Popolo, with the stories of her life, which were highly praiseworthy examples of that craft.
These works brought them no less fame and renown than comfort in life. But Maestro Claudio, being very intemperate in eating and drinking, according to the custom of his race, which is a deadly thing in the air of Rome, fell sick of so violent a fever, that in six days he passed to the other life. Whereupon Guglielmo, left alone, and almost like one lost without his companion, painted by himself a window, likewise of glass, in S. Maria de Anima, the church of the Germans in Rome; which was the reason that Cardinal Silvio of Cortona made him an offer, and made a contract with him that he should execute some windows and other works in his native city of Cortona. Wherefore the Cardinal took him in his company to take up his abode in Cortona; and the first work that he executed was the façade of the Cardinal's house on the side towards the Piazza, which he painted in chiaroscuro, depicting therein Croton and the other original founders of that city. Thereupon the Cardinal, who saw that Guglielmo was no less upright as a man than excellent as a master of that art, caused him to execute, for the Pieve of Cortona, the window of the principal chapel, in which he made the Nativity of Christ and the Magi adoring Him.
Guglielmo was a man of fine spirit and intelligence, and of very great mastery in handling glass, and particularly in so distributing the colours that the brightest should come in the foremost figures, those in the other figures being darker in proportion as they receded; in which point he was a rare and truly excellent master. Moreover, he showed very good judgment in the painting of his figures; whereby he executed them with such unity, that they fell back into the distance little by little, in such a way that they did not cling either to the buildings or to the landscapes, and had the appearance of being painted on panel, or rather in relief. He showed invention and variety in the composition of scenes, making them rich and well grouped; and he rendered easy the process of making such pictures as are put together out of pieces of glass, which was held to be very difficult, as indeed it is for one who has not his skill and dexterity. He designed the pictures for his windows with such good method and order, that the mountings of lead and iron, which cross them in certain places, were so well fitted into the joinings of the figures and the folds of the draperies, that they cannot be seen—nay, they gave the whole such grace, that the brush could not have done more—and thus he was able to make a virtue of necessity.
Guglielmo used only two kinds of colour for the shading of such glass as he proposed to subject to the action of fire; one was scale of iron, and the other scale of copper. That of iron, which is dark, served to shade draperies, hair, and buildings; and the other, that of copper, which produces a tawny tint, served for flesh colours. He also made much use of a hard stone that comes from Flanders and France, called at the present day hematite, which is red in colour and is much employed for burnishing gold. This, having first been pounded in a bronze mortar, and then ground with an iron brazing instrument on a plate of copper or yellow brass, and tempered with gum, works divinely well on glass.
When Guglielmo first arrived in Rome, he was no great draughtsman, although he was well practised in every other respect. But having recognized the need of this, he applied himself to the study of drawing, in spite of his being well advanced in years; and thus little by little he achieved the improvement that is evident in the windows that he afterwards made for the Palace of the said Cardinal at Cortona, and for the other without the city, in a round window that is in the aforesaid Pieve, over the façade, on the right hand as one enters the church, wherein are the arms of Pope Leo X, and likewise in two little windows that are in the Company of Gesù, in one of which is a Christ, and in the other a S. Onofrio. These are no little different from his early works, and much better.
Now while Guglielmo, as has been related, was living in Cortona, there died at Arezzo one Fabiano di Stagio Sassoli, an Aretine, who had been a very good master of the making of large windows. Thereupon the Wardens of Works for the Vescovado gave the commission for three windows in the principal chapel, each twenty braccia in height, to Stagio, the son of the said Fabiano, and to the painter Domenico Pecori; but when these were finished and fixed in their places, they gave no great satisfaction to the Aretines, although they were passing good and rather worthy of praise than otherwise. It happened at this time that Messer Lodovico Belichini, an excellent physician, and one of the first men in the government of the city of Arezzo, went to Cortona to cure the mother of the aforesaid Cardinal; and there he became well acquainted with our Guglielmo, with whom, when he had time, he was very willing to converse. And Guglielmo, who was then called the Prior, from his having received about that time the benefice of a priory, likewise conceived an affection for that physician, who asked him one day whether, with the good will of the Cardinal, he would go to Arezzo to execute some windows; at which Guglielmo promised that he would, and with the permission and good will of the Cardinal he made his way to that city. Now Stagio, of whom we have spoken above, having parted from the company of Domenico, received Guglielmo into his house; and the latter, for his first work, executed for a window of the Chapel of S. Lucia, belonging to the Albergotti, in the Vescovado of Arezzo, that Saint and a S. Sylvester, in so good a manner that the work may truly be said to be made with living figures, and not of coloured and transparent glass, or at least to be a picture worthy of praise and marvellous. For besides the mastery shown in the flesh-colours, the glasses are flashed; that is, in some places the first skin has been removed, and the glass then coloured with another tint; by which is meant, for example, the placing of yellow over red flashed glass, or the application of white and green over blue; which is a difficult and even miraculous thing in this craft. The first or true colour, then, such as red, blue, or green, covers the whole of one side; and the other part, which is as thick as the blade of a knife, or a little more, is white. Many, being afraid that they might break the glasses, on account of their lack of skill in handling them, do not employ a pointed iron for removing that layer, but in place of this, for greater safety, set about grinding the glasses with a copper wheel fixed on the end of an iron instrument; and thus, little by little, by the use of emery, they contrive to leave only a layer of white glass, which turns out very clear. Then, if a yellow colour has to be applied to the piece of glass thus left white, at the moment when it is to be placed into the furnace for firing, it is painted by means of a brush with calcined silver, which is a colour similar to bole, but somewhat thick; and in the fire this melts over the glass, fuses, and takes a firm hold, penetrating into the glass and making a very beautiful yellow. These methods of working no one used better, or with more ingenuity and art, than Prior Guglielmo; and it is in these things that the difficulty consists, for painting the glass with oil-colours or in any other manner is little or nothing, and that it should be diaphanous or transparent is not a matter of much importance, whereas firing it in the furnace and making it such that it will withstand the action of water and remain fresh for ever, is a difficult work and well worthy of praise. Wherefore this excellent master deserves the highest praise, since there is not a man of his profession who has done as much, whether in design, or invention, or colouring, or general excellence.
He then made the great round-window of the same church, containing the Descent of the Holy Spirit, and likewise the Baptism of Christ by S. John, wherein he represented Christ in the Jordan, awaiting S. John, who has taken a cup of water in order to baptize Him, while a nude old man is taking off his shoes, and some angels are preparing Christ's raiment, and on high is the Father, sending down the Holy Spirit upon His Son. This window is over the baptismal font of that Duomo, for which he also executed the window containing the Resurrection of Lazarus on the fourth day after death; wherein it seems impossible that he could have included in so small a space such a number of figures, in which may be recognized the terror and amazement of the people, with the stench from the body of Lazarus, whose resurrection causes his two sisters to rejoice amid their tears. In this work are innumerable colours, flashed one over the other in the glass, and every least thing truly appears most natural in its own kind.
And whoever wishes to learn how much the hand of the Prior was able to effect in this art, should study the window of S. Matthew over the Chapel of that Apostle, and observe the marvellous invention of that scene, wherein he can see a living figure of Christ calling Matthew from his tables, while Matthew, following Him and stretching out his arms to receive Him, abandons the riches and treasures that he has acquired. And at the same time an Apostle may be seen in a very spirited attitude, awaking another who has fallen asleep on some steps; and in like manner there may also be perceived a S. Peter speaking with S. John, both being so beautiful that they seem truly divine. In this same window are temples in perspective, staircases, and figures so well grouped, and landscapes so natural, that one would never think it was glass, but rather a thing rained down from Heaven for the consolation of mankind. In the same place he made the window of S. Anthony and that of S. Nicholas, both most beautiful, with two others, one containing the scene of Christ driving the traders from the Temple, and the other that of the woman taken in adultery; all these works being held to be truly excellent and marvellous.
So fully were the labours and abilities of the Prior recognized by the Aretines, what with praises, favours, and rewards, and so satisfied and contented was he by this result, that he resolved to adopt that city as his home, and to change himself from a Frenchman into an Aretine. Afterwards, reflecting in his own mind that the art of glass-painting, on account of the destruction that takes place every moment in such works, was no lasting one, there came to him a desire to devote himself to painting, and he therefore undertook to execute for the Wardens of Works of the Vescovado in that city three very large vaults in fresco, thinking thus to leave a memorial of himself behind him. The Aretines, in return for this, presented to him a farm that belonged to the Confraternity of S. Maria della Misericordia, near their city, with some excellent houses, for his enjoyment during his lifetime. And they ordained that when the work was finished, its value should be estimated by some distinguished craftsman, and that the Wardens should make this good to him in full. Whereupon he made up his mind to show his worth in this undertaking, and he made his figures very large on account of the height, after the manner of the works in Michelagnolo's chapel. And so mightily did his wish to become excellent in such an art avail in him, that although he was fifty years of age, he improved little by little in such a manner, that he showed that his knowledge and comprehension of the beautiful were not less than his delight in imitating the good in the execution of his work. He went on to represent the earlier events of the New Testament, even as in the three large works he had depicted the beginning of the Old. For this reason, therefore, I am inclined to believe that any man of genius who has the desire to attain to perfection, is able, if he will but take the pains, to make naught of the limits of any science. At the beginning of those works, indeed, he was alarmed by their size, and because he had never executed any before; which was the reason that he sent to Rome for Maestro Giovanni, a French miniaturist, who, coming to Arezzo, painted over S. Antonio an arch with a Christ in fresco, and for that Company the banner that is carried in processions, which he executed with great diligence, having received the commission for them from the Prior.