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TIPS
FOR USING CLEAR CASTING RESIN
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| Clear
cast is a low exotherm mass casting polyester resin used for clear
solid castings, imbediments and for coating table and bar tops.
This resin can be pigmented with translucent or opaque pigments if
desired. Clear cast cures with a surface tack which will cross
link with any subsequent layers that may be cast (poured). |
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| MOLD
SELECTION |
| In
order to gain casting experience the novice can utilize simple
molds of plastic food storage containers. These containers do not
need any release agent, as the resin does not stick to food grade
plastic containers such as Tupperware. With this type of mold the
casting is done face side down, so any objects that are to be
encapsulated are placed in the mold facing the bottom of the mold.
The usual procedure is to pour a shallow face layer of resin and
let it gel, add the imbediments and pour the mold full, let cure
and demold.
Custom
made molds of polyurethane rubber or RTV silicone are utilized to
duplicate original objects such as figurines, plaques or other art
objects. The rubber molds are excellent for reproducing detail and
are an accepted process for reproduction. The major drawback to
the rubber molds is that they act as a heat sink (absorb exotherm)
when polyester resin casting. This heat sink tendency creates a
condition on the surface of the casting called surface
degradation, (SD). SD is a sticky textured finish caused by a lack
of exotherm on the surface of the casting. Preheating of the mold
to 150 degrees F prior to casting will help to alleviate this
condition.
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| CATALYZING |
| Excessive
exotherm (heat) can result in unacceptable levels of resin
shrinkage and possible cracking. The degree of exotherm can be
controlled by the following variables: percentage of catalyst
used, volume of resin poured as a function of surface area, and ,
ambient temperature. In other words, for large volume pours with
little surface area, catalyst must be reduced significantly vis-à-vis
the same volume of resin spread over a much larger surface area.
Additionally, using the same example, a pour in cool conditions,
will require more catalyst than in warmer or hot ambient
temperature conditions.
In
order to control excess temperature and shrinkage, we suggest the
resin catalyzed as follows:
For a 1" or thicker poured layer, 2 drops of catalyst per
ounce of resin.
For a ½" to 1" thick poured layer, 4 drops of catalyst
per ounce of resin.
For ½" or less poured layer, 8 drops of catalyst per ounce
of resin.
The aforementioned catalyst levels assume there will be a surface
area of at least 6" x 6". Some trial and error testing
would be prudent for various shapes and sizes. The end result of
manipulating the catalyst level based on the size of the casting
is to minimize resin exotherm and shrinkage yet still cure to the
proper hardness.
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| IMBEDIMENTS |
The
variety of objects that can be imbedded in castings is limited
only by one's imagination. However, many objects require some
preparation prior to imbedding .
Porous materials will most likely vent air bubbles when submerged
in resin. Sealing the surface with a coat of the casting resin
(catalyzed) and allowing to cure before casting will usually
eliminate air bubbles. The specific gravity or density of an
imbediment is often overlooked when casting. If the object is
buoyant or lighter than the casting resin the imbediment will
probably float. To prevent embediments from floating they must be
glued down using the casting resin in small quantities. Allow the
resin to cure before continuing with the remainder of the casting.
Material that is dyed or painted should be tested for color
fastness before casting as the color may bleed into the casting.
Photographs, fabrics, paintings, prints and similar materials
should be tested for compatibility with the casting resin prior to
casting.
Any material that has a damp surface or damp consistency, such as
fresh plaster may inhibit the cure of the casting resin, test
before casting.
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| PIGMENTS
AND DYES |
Opaque
castings of various colors can be achieved by the use of pigments
formulated for use with polyester resins. When adding pigment to
casting resin add only enough pigment to make the liquid opaque.
Opaque pigments usually slow the curing process of casting resin,
so additional catalyst may be needed to get a proper cure. Too
much pigment can retard the curing process altogether so use
pigments sparingly.
The use of translucent pigments can give resin castings the unique
quality of color and clarity. Translucent pigments are available
from various manufacturers throughout the country. As a
substitute, a drop or two of opaque pigment dissolved in an ounce
of Aliphatic Alcohol (2-Propanol) will make a passable translucent
pigment. Once the opaque pigment is well dissolved into the
alcohol, add while mixing the colored alcohol into your casting
resin in small quantities until the desired hue is achieved.
Catalyze the resin as explained above. The colored alcohol will
most likely have a slightly grainy look due to the grind of the
selected pigment. Keep in mind that most pigments come from the
earth and are only colored dirt and are not completely
dissolvable.
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| FINISHING |
| For
flat level castings such as tabletops 5 mil Mylar film placed onto
the wet resin mass and carefully smoothed so no air bubbles or
wrinkles are between the Mylar and the resin. The Mylar film
allows the resin to cure in the absence of air, to completely
cross link and cure with a high gloss.
For
irregular shaped castings in a mold, a final thin layer of Clear
Cast resin with surfacing agent added will produce a slightly hazy
cured surface. The haze can be buffed away with a polishing
compound.
For
super high gloss for artistic castings the final layer of Clear
Cast can be blended with 50% Duratec Clear High Gloss Additive for
a tack free high gloss finish. The Clear Cast Duratec blend should
not exceed 1/8" thickness. All of the above techniques
require the addition of MEKP as described in the Catalyzing
section.
Certain
epoxy products, such as the Pro-Glas Deco epoxy, and System 3
Mirror Coat, provide excellent alternatives to polyester with the
caveat that ultraviolet exposure is not an issue (inside use
only). In addition, you will likely find these products much
easier to use.
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| THESE
TIPS ARE PROVIDED IN GOOD FAITH AND TO THE BEST OF OUR KNOWLEDGE
ARE ACCURATE. WE ASSUME NO RESPONSIBILITY FOR FAILURES RESULTING
FROM ADHERANCE TO THE ABOVE TIPS. ABOVE ALL HAVE FUN AND TEST,
TEST, TEST! |
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