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.