her 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. I