DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.11365#0036
25
the manufactures.
53. Among the furnace-waste were many pebbles
of white quartz. These had been laid as a cobble
floor in the furnace, and served as a clean space on
which to toast the pats of colour, for scraps of the
paste of frit were found sticking to one side of the
pebbles. This floor also served to lay objects on for
glazing, as the superfluous glaze had run down and
spread over the pebbles as a thin wash of green.
Doubtless this use of the pebbles was two-fold ; they
provided a clean furnace floor, and they became dis-
integrated by the repeated heating so that they were
the more readily crushed for mixture in the frits
afterwards.
The half-pan of uncombined frit shews exactly the
size and form of the fritting-pans, about 10 inches
across and 3 inches deep. Among the furnace-waste
were also many pieces of cylindrical jars, about 7 inches
across and 5 inches high. These jars almost always
had glaze run down the outside of them, from the
closed end to the open end ; the glaze is of various
colours, blue, green, white, black, etc., evidently leaked
from the pans of glass. Hence they must have stood
mouth downward in the furnace, to support the
fritting-pans and glass crucibles above the fire, as
shewn at the bottom of PL. XIII, 62.
54. Of the furnaces used for glass-making we have
no example ; but a furnace that was found near the
great mould and glaze factory was apparently used
for charcoal-burning, as a great quantity of charcoal
was found in it, but no trace of pans, jars, or glass.
This furnace (see Pl. XLII) was an irregular square
varying from 43 to 57 inches at the sides. It was
originally about 35 inches high, but the roof was
destroyed. The northern door was 29 high and 15
wide, to admit the north wind, and to serve for tend-
ing the furnace on the windward side. While the
south or exit door was 16 high and 13 wide, for the
gases to pass off. Probably the glazing furnaces were
on the same principle ; and perhaps even the same
furnace would be used for varying purposes.
55. Of the stages of production of the glass we
have a continuous series. The crucibles in which it
was melted were deeper than the fritting-pans ; being
about two or three inches in depth and diameter.
The form is shewn by the outlines of the pieces of
glass, and most fully by piece 40, Pl. XIII, which
gives a section of the vessel in which it cooled. Many
such pieces of glass are found retaining the rough
surface, and even chips of the crucible adhering to
them ; while the old top surface shews the smooth
melted face, with edges drawn up by capillary attrac-
tion. The upper part is often frothy and worthless.
This proves that the materials were fused in these
vessels, as the froth of carbonic acid expelled by
combination was yet in the vessel. If the glass had
been made eleswhere and then merely remelted here
it would have been clear. Moreover, by the manner
in which the crucible has in all cases been chipped off
the lump of glass after cooling, it is certain that the
glass was left to cool in the crucible ; so as to
gradually let the scum rise, and the sediment sink, as
is now done with optical glass. If the glass had been
poured out, we should not have found such pieces as
these; on the contrary we ought then to have found
masses of cast glass, which have never yet been dis-
covered. It is therefore plain that the glass after
melting was left to stand in the crucibles until the
furnace was cool; the blocks were then removed, the
crucibles chipped away, the defective parts of the
glass—scum and sediment—were chipped off, and a
clear lump of good glass was thus obtained for
working up.
While the glass was being made samples were
taken out by means of a pair of pincers, to test the
colour and quality ; and many of these samplings (as
PL. XIII, 41, 42) were found, shewing the impress of
the round-tipped pincers.
56. After obtaining the lumps of clear glass these
were broken up into suitable sizes, and heated to
softness. They were then laid on a fiat surface, and
rolled by a bar worked diagonally across them. This
method prevents flattening in the roll, which is liable
to occur in a pasty material if rolled at right angles
to the length. Also a rolled paste is liable (like
hammered iron rods) to become hollow in the middle
owing to over expansion of the outside, and so to
crack up lengthways. But by pressing only a short
length at once in rolling, by a diagonal bar, the rest
of the material holds it together and tends to prevent
splitting. Again, by rolling only a small area at once,
much greater pressure can be applied, and hence the
glass could be rolled cooler, and without such risk of
flattening. The marks of the diagonal rolling are
seen on the finished rolls, as on Pl. XIII, 43.
The next, stages, after thus obtaining thick rods of
glass, were to draw this out, as in producing what is
now known as " cane" ; or to flatten it into strips,
which were polished and used for inlaying, or else
drawn out like the rods, thus forming thin glass
ribbon. A third variety of drawn glass are the tubes,
Pl. XIII, 51, 52. How these were first made is un-
certain, probably by heavy rolling of the rods, so as
the manufactures.
53. Among the furnace-waste were many pebbles
of white quartz. These had been laid as a cobble
floor in the furnace, and served as a clean space on
which to toast the pats of colour, for scraps of the
paste of frit were found sticking to one side of the
pebbles. This floor also served to lay objects on for
glazing, as the superfluous glaze had run down and
spread over the pebbles as a thin wash of green.
Doubtless this use of the pebbles was two-fold ; they
provided a clean furnace floor, and they became dis-
integrated by the repeated heating so that they were
the more readily crushed for mixture in the frits
afterwards.
The half-pan of uncombined frit shews exactly the
size and form of the fritting-pans, about 10 inches
across and 3 inches deep. Among the furnace-waste
were also many pieces of cylindrical jars, about 7 inches
across and 5 inches high. These jars almost always
had glaze run down the outside of them, from the
closed end to the open end ; the glaze is of various
colours, blue, green, white, black, etc., evidently leaked
from the pans of glass. Hence they must have stood
mouth downward in the furnace, to support the
fritting-pans and glass crucibles above the fire, as
shewn at the bottom of PL. XIII, 62.
54. Of the furnaces used for glass-making we have
no example ; but a furnace that was found near the
great mould and glaze factory was apparently used
for charcoal-burning, as a great quantity of charcoal
was found in it, but no trace of pans, jars, or glass.
This furnace (see Pl. XLII) was an irregular square
varying from 43 to 57 inches at the sides. It was
originally about 35 inches high, but the roof was
destroyed. The northern door was 29 high and 15
wide, to admit the north wind, and to serve for tend-
ing the furnace on the windward side. While the
south or exit door was 16 high and 13 wide, for the
gases to pass off. Probably the glazing furnaces were
on the same principle ; and perhaps even the same
furnace would be used for varying purposes.
55. Of the stages of production of the glass we
have a continuous series. The crucibles in which it
was melted were deeper than the fritting-pans ; being
about two or three inches in depth and diameter.
The form is shewn by the outlines of the pieces of
glass, and most fully by piece 40, Pl. XIII, which
gives a section of the vessel in which it cooled. Many
such pieces of glass are found retaining the rough
surface, and even chips of the crucible adhering to
them ; while the old top surface shews the smooth
melted face, with edges drawn up by capillary attrac-
tion. The upper part is often frothy and worthless.
This proves that the materials were fused in these
vessels, as the froth of carbonic acid expelled by
combination was yet in the vessel. If the glass had
been made eleswhere and then merely remelted here
it would have been clear. Moreover, by the manner
in which the crucible has in all cases been chipped off
the lump of glass after cooling, it is certain that the
glass was left to cool in the crucible ; so as to
gradually let the scum rise, and the sediment sink, as
is now done with optical glass. If the glass had been
poured out, we should not have found such pieces as
these; on the contrary we ought then to have found
masses of cast glass, which have never yet been dis-
covered. It is therefore plain that the glass after
melting was left to stand in the crucibles until the
furnace was cool; the blocks were then removed, the
crucibles chipped away, the defective parts of the
glass—scum and sediment—were chipped off, and a
clear lump of good glass was thus obtained for
working up.
While the glass was being made samples were
taken out by means of a pair of pincers, to test the
colour and quality ; and many of these samplings (as
PL. XIII, 41, 42) were found, shewing the impress of
the round-tipped pincers.
56. After obtaining the lumps of clear glass these
were broken up into suitable sizes, and heated to
softness. They were then laid on a fiat surface, and
rolled by a bar worked diagonally across them. This
method prevents flattening in the roll, which is liable
to occur in a pasty material if rolled at right angles
to the length. Also a rolled paste is liable (like
hammered iron rods) to become hollow in the middle
owing to over expansion of the outside, and so to
crack up lengthways. But by pressing only a short
length at once in rolling, by a diagonal bar, the rest
of the material holds it together and tends to prevent
splitting. Again, by rolling only a small area at once,
much greater pressure can be applied, and hence the
glass could be rolled cooler, and without such risk of
flattening. The marks of the diagonal rolling are
seen on the finished rolls, as on Pl. XIII, 43.
The next, stages, after thus obtaining thick rods of
glass, were to draw this out, as in producing what is
now known as " cane" ; or to flatten it into strips,
which were polished and used for inlaying, or else
drawn out like the rods, thus forming thin glass
ribbon. A third variety of drawn glass are the tubes,
Pl. XIII, 51, 52. How these were first made is un-
certain, probably by heavy rolling of the rods, so as