A question has
been asked that relates to draping over a face mask mould, but this response relates to any drape with compound or multiple shapes.
The rate of
advance should be a steady one all the way to the forming
temperature. This should be 150C/hr or less. Thicker glass requires
a slower rate of advance to allow the glass to heat all the way
through. The point is to get the glass all the same temperature by
the time it reaches the forming temperature.
Draping
over an undulating mould takes more heat or time or both than simple
drapes, because there is a much greater variety of form for the glass
to conform to.
You have a
choice about the top temperature and soak times. You can choose a
low temperature with a long soak time, which most often leads to a
minimum of marks on the underside of the piece, but requires long
vigils at the kiln to determine when the drape is finished. The
other strategy is to go for a higher temperature and shorter soak,
which leads to more marks, but less time observing the firing. The
higher temperature may be as much as 720C.
Note that there
are a group of considerations about the size of the drape and the
thickness of the glass being draped.
There are some
things you can do to assist the progress of the drape. One, already
mentioned, is to increase the forming temperature.
Use a longer
time, or as much time as required. Watch the draping progress
because it is never certain how long the piece will take to conform
to the mould sufficiently.
Use props.
Place the props where the glass first starts to form just barely
supporting the edge of the glass. As the glass begins to bend, it
will slip off the supports - assuming they are well covered in
separators, even pieces of kiln paper. This means the folds will
start somewhere else than at the nose on a face mould or other high
point on any other form.
Manipulate the
glass. Reach in with wet wood sticks and push the glass about.
One stick will be needed to keep the glass in place while the other
pushes the glass about. The sticks do need to be both wet and
strong. If you use dry sticks they will mark the glass as well as go
on fire. Of course, you need protective gear to avoid burns to your skin and hair if you
do this.
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