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\technote{2}{Dan Ports}{2004/02/19}{drkp@mit.edu}
\tntitle{Some Plastics for Scenic Use}
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In addition to the wood and metal commonly used for constructing
scenery and props, plastics can be used in the building of many scenic
elements. There are a variety of plastic products useful in the
theater, far too many to describe in detail here; this note explores
the applications of a few of them.

\section*{Foam}
Many types of foams, or expanded plastics, are available. Perhaps the
most common is expanded polystyrene, generally known (if not
necessarily correctly) as Styrofoam or blue foam. This sort of foam is
very useful in other industries because of its compressive strength,
buoyancy, and thermal insulation. However, these properties are not
especially useful in the theater; instead, it is used because it is
lightweight (being composed mostly of air) and can be sculpted easily.
It can be used to create shaped three-dimensional scenic elements that
would be difficult to create using other materials.

Traditional tools such as knives and saws can be used to cut and
sculpt polystyrene foam, but a hot knife, capable of melting the foam,
can be used to make cuts more easily. This simple tool can be created
by connecting a power source (a couple batteries will serve as a
simple power supply) to a resistive nichrome wire, then mounting it on
an appropriate frame. This type of cutter can also be used by forming
the wire into the desired shape, then pushing the foam board through
it to shape it. 

Urethane foam is available in many forms, rigid and flexible foams of
various densities and sizes. Urethane foams often come as two-part
expanding mixtures, which can be sprayed or poured; when combined with
an appropriate mold, these can be very effective at forming many
complex shapes.

Polyethlene foam can be convenient for scenic decorations because it
is available as rounds rods of various diameters. It can be sliced and
used to make round moldings.

Working with these products introduces a set of safety concerns. Foams
can be flammable and can produce dangerous gases in a fire, so it is
important to use a flame-retardant, or purchase foam products that are
already treated. When working with foam, especially when using a hot
knife, toxic vapors may be released, so it is important to have
sufficient ventilation. Polystyrene foam is easily dissolved by many
chemicals, including many adhesives, spray paints, etc, so it is
important to use a coating (e.g. Sculpt or Coat) to prevent this. The
coating can also be used for texturing.


\section*{Thermoplastics}
Thermoplastics are materials which can be easily shaped when
heated. These materials were developed for the medical industry, and
in the theater can be useful for details on scenery and props. Their
high cost as compared to other materials makes it difficult to use
thermoplastics on a larger scale, though it is sometimes possible to
heat, reshape, and reuse old pieces. They are generally easy to work
with and do not release toxic fumes when heated.

When cold, thermoplastics can be manipulated using saws and sandpaper
and other conventional tools. When heated, they become flexible and
can be easily molded. Generally, hot water is used to make the plastic
shapable; it can then be shaped freehand or poured into a mold before
being allowed to cool and set. For reshaping smaller sections or
joining multiple pieces, a heat gun can be used to make them pliable.

Protoplast pellets and sheets are some of the most useful forms of
thermoplastic materials for construction: the sheets for constructing
rigid structures or smooth surfaces, and the pellets for shaping
details or for use in molds. Thermoplastic-covered fabrics and meshes
are also available, and are useful for texturing.

\section*{References}
\begin{itemize}
\item http://upstagereview.org/StagecraftArticles/chemical.pdf
\item http://www.pnta.com/thermots.html
\end{itemize}
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