the change is only every twelve hours, with suitable time for
The English blower works about forty-eight
or fifty-four hours; and the French, seventy-two hours per week.
The most important department of
Glass-making is the manufacture of the melting-pots.
For this purpose, the best
Stourbridge clay, in the lump, should be selected, and only that part
ground which is free from impurity: this peculiar fire-clay is usually
found in iron districts; the best is from Stourbridge, in Worcestershire;
it may be termed a silicate of alumine. Too much of the latter would
render it too fusible; and if in excess of silica, it would fail to cement
the mass efficiently, so as to bear the weight of the fluid Glass, viz.,
about eighteen hundred weight. Rather too much alumine is usually found
in this sort of clay, and pots stand better by having about one-fifth
in quantity of old pots ground, and used with four-fifths of new clay,
which mixture retains sufficient tenacity. The ground potsherd not
only assists to dry the pots more regularly, but it renders the whole
body more porous, and less likely to split by sudden heat. Very few
manufacturers use pots made from new material only.
The chamber where the clay is kneaded,
and the pots are