On Painting Glass Windows and how they are put together with Leads and
supported with Irons so as not to interfere with the view of the
figures.
§ 101. _Stained Glass Windows; their Origin and History._
Formerly the ancients were in the habit of filling in their windows, but
only in the houses of great men, or of those at least of some
importance, in such a manner as to prevent the wind or cold from
entering, while not excluding the light. This plan was adopted only in
their baths and sweating rooms, vapour baths and other retiring rooms,
and the apertures and vacant places of these were closed with
transparent stones, such as onyx marbles,[264] alabasters, and other
delicate marbles that are variegated or that incline towards a yellowish
tint. But the moderns, who have had glass furnaces in much greater
abundance, have made the windows of glass, either of bull’s-eyes[265] or
of panes, similar to or in imitation of those that the ancients made of
stone; and they have fastened them together and bound them with strips
of lead, grooved on both sides, and furnished them and secured them with
irons let into the walls for this purpose, or indeed into wooden
frames,[266] as we shall relate. Whereas at first the windows used to be
made simply of clear bull’s-eyes with white or coloured corners,
afterwards the artists thought of making a mosaic of the shapes of these
glasses differently coloured and joined after the manner of a
picture.[267] And so refined has the skill in this art become, that in
our days glass windows are seen carried to the same perfection that is
arrived at in fine pictures upon panel, with all their harmony of colour
and finish of execution, and this we shall amply show in the Life of the
Frenchman Guglielmo da Marcilla.[268]
In this art the Flemings and the French have succeeded better than the
other nations, seeing that they, with their cunning researches into
pigments and the action on them of fire, have managed to burn in the
colours that are put on the glass, so that wind, air, and rain may do
them no injury, whereas formerly it was customary to paint windows in
colours coated with gum and other temperas that wasted away through time
and were carried off by the winds, mists, and rains, till nothing was
left but the mere colour of the glass. In the present age, we see this
art brought to that high grade beyond which one can hardly desire
further perfection of fineness and beauty and of every quality which
contributes thereto. It supplies a delicate loveliness not less
beneficial to health, through securing the rooms from wind and foul
airs, than useful and convenient on account of the clear and unimpeded
light that by its means is offered to us.
In order to produce such windows, three things are necessary, namely,
luminous transparency in the glasses chosen,[269] beautiful arrangement
in that which is worked out with them, and clear colour without any
confusion. Transparency is secured by knowing how to choose glasses that
are clear in themselves, and in this respect French, Flemish, and
English glasses are better than the Venetian,[270] because the Flemish
are very clear and the Venetian much charged with colour. In clear
glasses when shaded with darker tints the light is not totally lost,
they are transparent even in their shadows, but the Venetian, being
obscure in their nature and darker still in their shadow, lose all
transparency. Again many delight in having the glasses loaded with
colours artificially laid on so that when the air and sun strike upon
them, they exhibit I cannot tell how much more beauty than do the
natural colours; nevertheless, it is better to have the glasses clear in
their own substance, rather than obscure, so that when heavily coloured
they may not be left too dim.
§ 102. _The Technique of the Stained Glass Window._[271]
For painting on glass, we must first have a cartoon on which are drawn
the outlines of the figures and of the folds of the drapery. These show
where the pieces of glass have to be joined; then the bits of red,
yellow, blue, and white glass must be picked out and divided according
to the design for the flesh parts and for the draperies, as occasion
demands. To bring each piece of glass to the dimensions traced on the
cartoon, the said pieces are laid on the cartoon and the outline marked
with a brush dipped in white lead, and to each piece is assigned its
number in order to find it easily when joining them together; when the
work is finished the numbers are rubbed off. When this is done, in order
to cut the pieces to measure, the workman, having first drawn an emery
point over the upper surface of the glass along the outline, which he
damps with saliva, takes a red-hot pointed tool and proceeds to pass the
point along the outlines, keeping a little within them; as he gradually
moves the tool, the glass cracks and snaps off from the sheet. Then with
the emery point he trims the said pieces, removing the superfluous part,
and with a tool called ‘grisatoio’ or ‘topo’ (grozing iron) which
nibbles the traced edges, he makes them exact and ready to be joined all
round.
In this manner then the bits of glass fitted together are spread on a
flat table above the cartoon, and the artist begins to paint in the
shadows over the draperies, using for this the ground scales of iron and
of another rust[272] found in iron pits, which is red, or else hard red
haematite finely ground, and with these pigments he shades the flesh,
using alternately black and red, according to need. To produce the flesh
tints it is necessary to glaze all the glasses with this red, and the
draperies with the black, the colours being tempered with gum,[273] and
so gradually to paint and shade the glasses to correspond with the tints
on the cartoon. When this process is finished, the worker, desiring to
put in the brightest lights, takes a short thin brush of hog’s bristles
and with it scratches the glass over the light, and removes some of that
coat of the first colour that had been given all over, and with the
handle of the brush picks out the lights on the hair, the beard, the
drapery, the buildings, and the landscapes as he sees fit. There are
great difficulties however in this work; and he who delights in it may
put various colours on the glass, for example, if he trace a leaf or
other minute object over a red colour, intending it to come out in the
fire a different tint, he removes from the glass a scale the size of the
leaf, with the point of a tool that pares away the upper surface of the
glass. This must be the first layer and not more; by so doing, the glass
remains white[274] and can be tinged afterwards with that red[275] made
of many mixtures, which when fused by heat becomes yellow. This can be
done with all the colours, but the yellow succeeds better on white than
on other colours; when blue is used to paint in the ground, it becomes
green in the firing, because yellow and blue mixed make a green colour.
This yellow is never used unless at the back of the glass where it is
not painted,[276] because if it were on the face it would mingle and
run, so as to spoil and mix itself with the painting; when fired however
the whole of the red remains on the surface, this, when scraped away by
a tool leaves the yellow visible.[277]
After the glasses are painted they must be put into an iron muffle with
a layer of sifted cinders mixed with burnt lime, and arranged evenly,
layer by layer, each layer covered with these ashes; they are then put
into the furnace, in which at a slow fire they are gradually heated
through till both cinders and glasses begin to glow, when the colours
thereon become red hot and run and are incorporated with the glass. In
this firing the greatest care must be taken, because a too violent heat
would make the glasses crack and too little would not fix the colours.
Nor must they be taken out till the pan, or muffle, in which they are
placed is seen to be red hot, as well as the ashes, with some samples
laid on the top to show when the pigment is liquefied.
After this the leads are cast in certain moulds of stone or iron. The
leads have two grooves; that is one on either side, within which the
glass is fitted and pressed tight.[278] The leads are then flattened and
made straight and fastened together on a table. Bit by bit all the work
is leaded in many squares and all the joinings of the lead soldered by
means of tin soldering irons. Across it in parts are iron rods bearing
copper wires leaded in to support and bind the work, which has an
armature of irons that do not run straight across the figures, but are
twisted according to the lines of the joinings, so as not to interrupt
the view of the figures. These are rivetted into the irons that support
the whole, and they are made not square but round that they may
interfere less with the view. They are put on to the outside of the
windows and leaded into holes in the walls, and are strongly bound
together with copper wires, that are soldered by means of fire into the
leads of the windows. And in order that boys and other nuisances should
not spoil the windows, a fine network of copper-wire is placed behind
them. These works, if it were not for the too fragile material, would
last in the world an infinite time. But for all this it cannot be said
that the art is not difficult, artistic, and most beautiful.