Using Casting Resin 
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TIPS FOR USING CLEAR CASTING RESIN

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).

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.

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--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 " to 1" thick poured layer, 4 drops of catalyst per ounce of resin.
For " 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.

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.
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.
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.

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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