Glues
have two major uses in fusing. One is to stick things together after
being fused (cold fusing). The other is to hold things together
before fusing.
Holding
things together while preparing the piece to be transferred to the
kiln is a major use of low tack adhesives and glues. All of these
burn off a lot lower than the temperature at which the glass begins
to stick together. So, if you are gluing overhanging pieces, for
example, they can move after the glue has burned off. If you
are assembling pieces that will not stay in place while you are
putting it together, glue will not help get the final result you
want. If you are gluing to keep things stable while you move it
to the kiln, you may find everything is ok.
However,
glue tends to boil off if the temperature is raised too fast. During
this process, the effect of the boiling will move the glass pieces
that are most unstable. This also occurs if you use too much glue.
You should only use as much as will stick the pieces together. Also
too much glue leads to black spots and sometimes bubbles between the
layers of glass.
The
adhesives commonly used are the Bullseye product “Glastac”,
Elmer’s glue, diluted PVA - or school - glue. All of these take
varying times to dry and hold the glass pieces in place. So, a
popular alternative is hair spray. This is a lacquer which dries
almost instantly. It provides a thin film of adhesive and burns off
in the kiln with no residue. You should use the varieties with no
additives.
Glue
most often leads to problems or unexpected results, so several ways
have been used to achieve the desired results.
One
way to deal with unstable components on small pieces is to make a
large piece with a repetition of the design and cut it up after
fusing in to the sizes you want. Clean the pieces very well,
and then fire them again to at least fire polish to remove any
cutting or grinding marks.
An
alternative to using glue, especially at the edges where the pieces
are likely to move, is to use dams. My practice is to make the dams
slightly taller than the unfired piece and line with fibre paper. I
put 3 mm fibre paper against the dam, and thinfire against the glass.
Both of these should be 3 mm narrower than the final height of the
fused piece will be. This is to allow the glass to make a rounded
edge as it will not be able to stick to the fibre as it sinks down to
its final height.
Another
alternative to using glue is to fire the piece upside down, so that
the pieces do not have to be supported. This does require some
planning and forethought. You can draw the design in reverse on
thinfire, using different coloured pencils for the various layers to
help in building the piece up in reverse. You then cap the assembled
pieces with the piece that will become the bottom. Take the whole to
a tack fuse. Then clean very well to remove any residues from the
shelf. It is possible to sandblast and then clean to make sure there
are no residues left. Of course this is not possible if you are
using dichroic or iridised glass. Also note that iridised surfaces
and thinfire do not get on well – there is extreme pitting in the
iridised surface.
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