It is natural that
we should want to put as much onto the shelf as we can to maximise the number of pieces
from each firing. But, when you are placing
the pieces remember that glass expands as it heats up. When the glass is at its
maximum expansion, it will be much less viscous than at lower temperatures and
so will stick very easily to any neighbouring piece it touches.
Although the final
size of a two-layer piece is the same at the end as the beginning, they do
expand to a larger size during the fusing process. My experience shows me that a 6mm piece can
expand as much as 5mm, depending both on temperature and size. This means that I treat 10mm as the absolute
minimum space between pieces. But, because of the size of my fingers, my normal
minimum placing is 20 mm apart as that is a comfortable space between my fingers and the other glass.
Thicker pieces
expand to become larger after fusing than they were at the start. These pieces
spread more during the firing than the 6mm piece. A 9mm piece may expand by about 3mm at the
finish – depending on size and temperature.
But during the firing, it may expand as much as 9mm. This means that
20mm is an absolute minimum between pieces that are 9mm thick at the edges,
even though they may be only 6mm over most of the area.
The tip is to avoid
over-filling your kiln shelf. By trying
to get too much production in one firing you may find a number of pieces stuck
together at the end, thus eliminating any savings on glass or space.
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