OVERSPRAYS AND ADHESIVES
Oversprays are solutions which are applied to the
surface of the glass prior to firing. Commonly called "devit
sprays," they are used to prevent devitrification, the scummy white layer
that can crystallize on the surface of the glass. They are available
commercially under several different names (Spray "A", Clear Coat
Overglaze, Super Spray) or you can mix up your own version using borax and
water. Some of these products contain lead and are not safe for food-bearing
surfaces, while others are food-safe.
Applying overspray can be done with a brush or by spray. In either case, it’s
important to apply the spray evenly to minimize "puddling." Applying
too much may result in a dull appearance, while not applying enough will keep
the spray from doing its job. Be sure to allow the overspray to dry thoroughly
before firing.
Many devit sprays will destroy or degrade the iridescent coating on glass, so
fire with the coated side down if you are using a spray. Sometimes you can mask
off the iridescent coating so that the spray doesn’t come into contact with
the glass. This can also be a useful design technique.
ADHESIVES
Adhesives are often used to secure one piece of glass to another prior to
fusing. The purpose is to make sure the two pieces stay in place until the glass
heats enough for fusing to take place. Aside from its adhesive quality, the main
characteristic desired of glues used for this purpose is to burn out without
leaving a trace.
Standard PVA white glues (such as Elmer’s brand in the US) or
"carpenter" glues work well, as do other glues such as Aleene’s
thick designer "tacky glue." Many fused glass artists report better
results when they mix the glue with water (a 50-50 mixture, or even more
diluted). You may also
purchase glues especially made for securing one piece of glass to another prior
to fusing.
A totally different kind of adhesive is used to permanently attach one piece
of glass to another. This is done outside the kiln and may also be useful for
creating shapes and sculptures that would be impossible to create in the kiln.
The strongest adhesive in this class is an epoxy called Hxtal. Quite
expensive, and requiring precise measurement to use, this epoxy must be
thoroughly mixed and applied to scrupulously clean surfaces. It takes up to a
week to cure completely, but is nevertheless favored for its strength and
clarity.
A second kind of permanent adhesive is ultraviolet (UV) glue, which cures
under ultraviolet light (sometimes the sun can be used). It dries clear in a
relatively short time, resists yellowing, and forms a strong bond.
Unfortunately, since it relies on light to activate and cure the glue, it can
only be used on transparent glass. Also, UV glues have a relatively short
lifespan and should be protected from sunlight.
One final type of commonly used glass adhesives are the silicones. This glue,
which was one of the first strong glues developed for glass, bonds firmly but
flexibly. The slight movement it allows helps keep the glass from cracking from
being held too tightly. Some silicones have a tendency to yellow, however, so
test the variety you use before doing extensive gluing.
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