Many props and figurines are cast using a two-part urethane resin that takes great detail and cures quickly. Air bubbles can be an issue with both molding and casting. With molding it is best to use a vacuum chamber if you have one available, and with resin casting it is best to have a pressure chamber to avoid air bubbles on the surface of your cast. For RTV rubber molds, a good technique sans vacuum chamber is to pour the rubber from about 6 feet high so it forms a tiny stream devoid of bubbles. You then patiently fill the mold cavity and wait for the rubber to cure. Good casts can be obtained from resin even without a pressure chamber by pre- paring the surface of the rubber mold before casting. Air bubbles tend to be attracted to the rubber surface, but you can break that attraction by coating the surface with marble dust or spraying the surface with a plastic paint primer. The advantage of the
primer method is that it not only helps to eliminate bubbles but also bonds to the slick resin and primes the surface so that you can paint the cast as soon as it comes out of the mold. To mix urethane resin, you just add equal amounts of parts A and B by volume and pour the mixture into the mold. Tap the mold while the resin is still liquid to force air bubbles to the surface and away from the figure area. When the mixture starts to cure it will generate a bit of heat, so care should be taken at this stage. After about 5 to 15 minutes, you can easily remove the cast and start the painting process.
Painting Materials
A tremendous variety of paint material is available today. For the sake of brevity, I’ll mention only a few that I feel are quite useful.
Figure 9.11 Two-part resin is a fast and easy casting material. This material can also be found atmonsterclub.com.
Primer
A primer coat is a substance that seals a surface and aids in the ability of paint to stick to an object. Wood, for example, is a porous substance that can be difficult to paint as it will absorb the solvent in paint and disrupt its ability to dry and cover adequately. A primer seals the wood and gives the paint something to adhere to. If you use a wood stain, there is no need for a primer as you are relying on the porosity of the wood to absorb the stain and bring out detail. Materials such as urethane resin have the opposite effect and are so slick and resistive that paint will not stick to them unless you use a primer. Some paints that have come on the market are self-priming, allowing you to skip this step.
Acrylic
For model building and figure painting, an inexpensive basic color kit of acrylic paint works very well. Liquitex makes a variety of kits that can be found at your local art store (visit www.liquitex.com). Acrylic is water soluble, is easy to work with, dries fast, and adheres well to most surfaces. The paints come in tubes in a variety of base colors. This paint can be used as is or diluted with water to create watercolor-style washes. The product was developed as an alternative to traditional oil paint.
Oil Paint
Traditional oil paint has been used for years as the primary medium for fine art paintings. It is so versatile that visual effects artists such as
Albert Whitlock chose to use this medium for their matte painting work. Because it has a slow drying time, the artist has the ability to do soft blends and feathering without having to worry about the paint drying before the artist finishes. Once the paint dries, the artist can paint transparent tones and glazes on top of the painting to add another dimension to the image. Whereas oil has been the medium of choice for many artists, others have been frustrated by the slow drying times and have also found themselves allergic to the oil and turpentine needed for its implementation.
Genesis Heat-Set Oil Paint
A new product called Genesis Heat-Set Artist Oils, manufactured by AMACO, addresses the toxicity and long drying times that have been the drawback to traditional oil paints. This terrific paint comes in a wide assort- ment of colors along with a thinning medium. The main advantage of using Genesis paint is that it will not dry until it is exposed to heat reaching 265°F to 280°F (130°C to 138°C) for several minutes. Once the paint
has dried, you can paint another layer and build up effects at your leisure, just as with traditional oil paint. The painted object can either be placed in a home oven or be exposed to hot air from a heat gun to cure the paint. You must be careful to ensure that what you are painting can withstand this temperature and not be destroyed by the heating process.
Enamel Paint
Enamel is the paint most commonly used for styrene plastic model kits. It comes in small vials in an assortment of colors. The paint is thinned with a solvent and can generate a smooth, even finish. Be aware that these paints are not uni- versally friendly to all plastics. If you use enamel paint on Sculpey, for example, the paint will lose its ability to dry and remain permanently tacky, spoiling both the paint job and the model. If you are unfamiliar with paint, be sure to test it on a scrap piece of the material you wish to paint.
Spray Paint
A trip to the local hardware store will expose you to a wide assortment of wonderful spray paint options. Today we have spray paint specifically designed to adhere to plastics and not attack them as I mentioned with enamel paint. Some paints are formulated to generate texture within the paint, such as Fleck Stone manufac- tured by Plasti-Kote (www.plasti-kote.co.uk). Texture paints are great tools for creating rough stone surfaces quickly. Some spray paints even simulate metal and chrome as long as it is sprayed on a smooth enough surface. Be sure to spray in a well-ventilated area or outdoors. If you do spray outdoors, be aware of the wind, as it is easy to get carried away spraying your model with white paint and ignore the fact that the wind is depositing some of your paint onto your neighbor’s black car.
Preval Paint Sprayer
Even with all the colors offered by spray paint manufacturers, I have often been frustrated with not finding an exact tint I need. This is especially true for the myriad of skin tones used for a variety of characters. A good tool for solving this problem is the Preval paint sprayer (www.prevalspraygun.com). This is a clever device that essentially lets you create your own spray paint can. You mix your paint or any other liquid in the glass canister provided, screw on the charged canister, and you have an instant paint sprayer for your custom color.
Faux Painting Kits
There are also many paint kits for simulating marble and other materials. One of the more successful material mimics is a kit manufactured by Sophisticated Finishes called the Bronze Antiquing Set (www.patina.com). This paint consists of actual powdered metal in a liquid binder. It offers an extremely effective way to simulate Figure 9.13 Genesis heat set oils has all the advantages of the tra-
a bronze figure. The other plus about the kit is that it has a second ingredient that acts as an oxidizer. Once the base coat of metal becomes tacky, you can apply the oxidizer and it will attack the metal to create an authentic patina finish.
Painting Rubber
It has always been a challenge to paint rubber, as the material flexes and therefore prevents many paints from sticking to it. Although there are specialty industrial paints formulated for rubber, such as Rubberbond (www .parasolinc.com), most model makers choose the less expensive solution of blending acrylic art paints, such as Liquitex, with rubber cement. The paint adds the color and the cement adds the bonding and flexibility. It is usually a good idea to add pigment to the foam rubber mixture to create the base color in the cast. After curing, the fine details can be added using the acrylic/rubber cement mixture. www.silpak.com recommends using vinegar to prime the latex surface and xylene to thin the rubber cement and acrylic paint mix. Alter- natively, you can blend acrylic paint with raw latex and use that combination to paint the model.
Brushes
It is most cost affective to purchase a kit of fine art brushes made from synthetic nylon. The kits are relatively inexpensive, come in a variety of brush sizes, and are easily cleaned. It is best to start with student brush kits until you are comfortable with painting techniques. You can then decide if you want to move on to the more expensive sable brushes. In the majority of situations, synthetic materials work just fine. Inexpensive synthetic brushes are a must when working with latex rubber, as they can easily be destroyed using this material.