Some who use two furnaces partly melt the mixture in the first, and
not only re-melt it in the second, but also replace the glass articles there.
Others partly melt and re-melt the material in different chambers of the
second furnace. Thus the former lack the third furnace, and the latter,
the first. But this kind of second furnace differs from the other second
furnace, for it is, indeed, round, but the interior is eight feet in diameter
and twelve feet high, and it consists of three chambers, of which the lowest is
not unlike the lowest of the other second furnace. In the middle chamber
wall there are six arched openings, in which are placed the pots to be heated,
and the remainder of the small windows are blocked up with lute. In the
middle top of the middle chamber is a square opening a palm in length
and width. Through this the heat penetrates into the upper chamber,
of which the rear part has an opening to receive the oblong earthenware
receptacles, in which are placed the glass articles to be slowly cooled. On
this side, the ground of the workshop is higher, or else a bench is placed there,
so that the glass-makers may stand upon it to stow away their products
more conveniently.
Those who lack the first furnace in the evening, when they have accomplished their day's work, place the material in the pots, so that the heat during
the night may melt it and turn it into glass. Two boys alternately, during
night and day, keep up the fire by throwing dry wood on to the hearth. Those
who have but one furnace use the second sort, made with three chambers.
Then in the evening they pour the material into the pots, and in the morning,
having extracted the fused material, they make the glass objects, which they
place in the upper chamber, as do the others.
The second furnace consists either of two or three chambers, the first of
which is made of unburnt bricks dried in the sun. These bricks are made of a
kind of clay that cannot be easily melted by fire nor resolved into powder ;
this clay is cleaned of small stones and beaten with rods. The bricks are
laid with the same kind of clay instead of lime. From the same clay the
potters also make their vessels and pots, which they dry in the shade. These
two parts having been completed, there remains the third.
The vitreous mass having been made in the first furnace in the manner
I described, is broken up, and the assistant heats the second furnace, in order
that the fragments may be re-melted. In the meantime, while they are doing
this, the pots are first warmed by a slow fire in the first furnace, so that the
vapours may evaporate, and then by a fiercer fire, so that they become red
in drying. Afterward the glass-makers open the mouth of the furnace, and,
seizing the pots with tongs, if they have not cracked and fallen to pieces,
quickly place them in the second furnace, and they fill them up with the
fragments of the heated vitreous mass or with glass. Afterward they close
up all the windows with lute and bricks, with the exception that in each
there are two little windows left free ; through one of these they inspect the
glass contained in the pot, and take it up by means of a blow-pipe ; in the
other they rest another blow-pipe, so that it may get warm. Whether it
is made of brass, bronze, or iron, the blow-pipe must be three feet long.
