Static Dispersing Glazing - Picture Framing Magazine

areas in the framed paper would heat up most rapidly,
since dark materials absorb heat more than light ones
and that such differential heating would result in a pattern
that would show up in the salt that forms from the
sodium that is driven from the glass by water. This pattern
can be seen on glass that has been left on frames for
many years. However, this salt will cling tightly to the
glass and should not pose much of a physical problem
for the framed paper. The static
that built up on the glass would
pose a problem for media such as
pastel and charcoal, but physical
contact and transfer were a
greater threat.
In the past, knowledge of this
problem led to unusual techniques.
For example, framers in
the 19th century were well aware
of the fact that pigment could
transfer from the art design to the
glass. They understood that the
greatest risk came from the possibility
that pigment might be
moved from one part of the
design to another, blurring it.
One solution they had for this
problem was placement of the
pastel directly behind the glass.
To ensure that there was minimal
movement of pigment among parts of the drawing, they
kept the pastel snug to the glass by placing cotton
between the back of the paper and the wooden backing.
Even though this resulted in a certain quantity of the
pigment moving from the design to the glass, it guarded
against loss of clarity in the design.
Modern framing has used deep matting and spacers
to address the contact transfer issue and until recently,
went on the assumption that the static potential of glass
was not a significant problem. That view was altered
when staff at the Tate Gallery in London observed that
the process of taking tape off of glass created a significant
static charge. This meant that the tape that had
been used to prevent shattered glass from coming loose,
if there was breakage during shipment, presented a
problem. In short, to maintain safety, the pastel would
have to be unframed, before the tape could come off of
the glass. Museums have used laminated glass to avoid
both breakage and taping issues. Such glass has been
88 PFM _ December 2004
An anti-reflective,
static dispersing acrylic
can be cut with hand
tools or a wall cutter.
Cutting the material
with a saw may cause
some of the brittle
surface coatings to chip.
expensive and hard to work with, since few have had the
ability to cut it to size.
A simple solution to both problems comes from
shatter-resistant acrylic sheet that has a static dispersing
coating of metallic material on its surface. Both glass
and acrylic can be coated with different materials, for
different purposes. Alternating layers of silicates and
titanium dioxide can be used to change the phase of
reflected light as it leaves the glazing.
This makes the reflected light opposite
in phase to the incoming light
and thus, the reflection is cancelled.
This produces the anti-reflective
coatings that are so useful for glazing
dark items.
There are two processes for
applying such coatings. The sheets
can be dipped in a bath and the
material can be baked onto the surface.
Such coatings can also be
applied with an ionic sputter coater.
The first process can only be done
with glass, while the second process
can be done with either glass or
acrylic sheet. To keep the acrylic
from warping at the elevated temperatures
inside the sputter coater, the
use of acrylic that has abrasion resistant
coating on it has been shown to
work well. If another coating of a metallic compound
such as indium-tin oxide is added, these metal oxides
disperse any static that the sheet may encounter, rendering
it static free.
Static dispersing acrylic can be found in sizes up to
48"x96" and thicknesses as great as 1 /4". It is used in
clean rooms, where critical scientific and technical tasks
are carried out. (This product can be found in the
online catalog of McMaster Carr.) Another, even more
useful form of static dispersing acrylic comes 41"x71"
and as thick as 3 /16"; it has the advantage of anti-reflectivity
and it is available with UV filtration. This material
was developed for use in flat screen electronic devices,
where the potential for static is quite high and the
client’s investment warrants the use of premium materials.
This latter material is available from Tru Vue, under
the name Optium. Both the non-UV filtering and UVfiltering
sheets of Optium are available in 1 /8" and 3 /16"
thicknesses; the thinner of the two can serve the needs