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How To.. Contents

• Powder Coating Technique

• Metal Cold Casting

• Cast Marble Effect

• Adding Color Tints

• Wood Grain Effect

Powder Coating Technique Yields Paint-Ready Castings

Dreams To Reality Studios (Norristown, PA) does production resin casting for a number of clients around the U.S. and Canada, and is always looking for innovative ways to reduce costs and save time. One technique that DTR uses involves Ease Release 200 mold release agent, which continues to be our best seller for rapid prototyping and casting.

The Specifics – DTR Studios recently secured a job to produce a few hundred model horses using a fast set polyurethane resin.

The horse model was sculpted in clay and molds made using silicone rubber. Prior to casting the resin, Ease Release 200 is applied to the mold followed by a powder coating of ATH (aluminum trihydrate).

An air hose is used to blow any excess powder from the mold. The urethane resin is then cast into the mold and demolded in about 10 minutes.

The casting comes out of the mold perfectly dry with a matte finish, and shipped to another location for painting. An auto body primer is applied, followed by an acrylic paint and finally an acrylic sealer. The major advantage to powder coating is that there is no release agent to remove when the casting comes out of the mold. Models can be immediately primed and painted.

DTR President, Michael Kryger, selected the Ease Release 200 for two reasons: 1) applying the release agent to the silicone mold resulted in longer mold life and 2) the ER200 does not go on heavily and is readily absorbed by the ATH powder.

The labor and time savings realized by employing this technique is significant.

Metal Cold Casting With Smooth-Cast™ 325

There are different techniques used to achieve a metallic finish with a resin. “Cold-Casting” is a term used to describe the process of mixing metal powder with a resin and applying the mixture into a mold.  The finished casting gives the appearance and weight of solid metal. The metal cold-cast process is faster and much less expensive when compared with foundry casting of molten metal (lost wax process).  Different metal powders such as bronze, brass, nickel-silver and copper can be used depending on the desired effect. 

Overview - To make a metal cold-casting, metal powder is mixed into the resin until the mixture is thick and creamy. The mixture is then “slush-cast” (poured into a mold and rolled around) or brushed onto the mold surface (gel coat) until the resin cures. The gel coat is then back-filled with straight resin, resin mixed with metal powder, resin mixed with lead shot (for weight) or Foam-iT! 5 rigid foam.

Specifics - Cold Cast Bronze - Our example will detail making a cold-casting using bronze powder (also referred to as “bonded bronze”) by first applying a “gel coat” layer and then adding more resin on top of the gel coat (back filling).

Materials Needed:    A. Bronze Powder*    B. Casting Resin    C. Liquid Pigment (Black)

A. Bronze Powder - Recommended metal powder mesh size for mixing with resin is –325.  Metallic powders are available from Smooth-On and its distributors.

B. Casting Resin - Smooth-Cast 325 Colormatch works best because it is a neutral clear amber and readily accepts metal powders and/or pigments.  Also, SC 325 has no odor.

C. Liquid Pigment - Adding a dark pigment (black or dark brown) to the resin/bronze powder mixture will give the final casting added definition and dimension.

Also required: Rubber Mold;  Mold Release Agent; measuring and mixing containers; mixing paddles; 1” paint brushes.

Amount of resin, bronze powder and pigment required will vary depending on the desired effect.  The mixing ratio can be as low as 1A : 1B : 1 Metal Powder.   Using more metal powder gives the finished casting greater weight thereby simulating the weight of real metal castings (i.e. 1A : 1B:  3 Metal Powder).   However, the addition of steel or lead beads to the “back-fill” resin can also be used to add weight at a much lower cost than the metal powder. For this example, we will use the following:

        Part B of Resin:  1 Part             Bronze Powder:  1 Part

          Part A of Resin:  1 Part             Liquid Pigment:   0.1 Part (small amount)

1.  Apply Release Agent to Rubber Mold** - To prevent resin mixture from sticking to rubber mold, thoroughly spray mold release agent over entire mold surface.  Brush into all surface detail and follow with second light mist coating of release agent and let dry for 15 minutes.

2.  Mix Metal Powder and Pigment with Part B of Resin - To allow ample mixing time, mix metal powder and pigment thoroughly with Part B of SC 325 (Blue Label) prior to adding Part A (Yellow Label).  Dispense 1 part of Part B into clean mixing container.  Add 1 part of bronze powder and 0.1 (small amount) part of black pigment to Part B and mix thoroughly. 

3.  Add 1 part of Part A - to the Part B/bronze powder/pigment mixture and mix thoroughly.  

4.  Gel Coat – Brush mixture into the mold cavity. The objective is to coat mold surface thoroughly until mixture begins to set up or “gels”.  Continuously brushing mixture up onto all vertical surfaces until mixture begins to thicken will ensure a uniform coating.   Allow gel coat to cure 15 minutes.

5.  Back-fill - with resin, resin mixed with metal powder, or Foam-iT! 5. 

     Tip:   Adding steel or lead beads to this mix gives the finished piece the weight 
ne  necessary to simulate the feel of a real solid bronze casting.   Fill almost to top,
     leaving3/8” (0.95 cm) headspace.  Let this mixture gel and cap remaining headspace
     with SC SC 325 resin pigmented with dark brown pigment or SC 325 resin and bronze
      powder to closely match the color of gel coat.

6.  Entire casting should be thoroughly cured before demolding - Remember: the resin/bronze mixture or filled resin will take longer to harden than unfilled resin.  Cure time depends on size of casting, mold configuration, amount of fillers used, etc.  Generally 30 to 40 minutes is a sufficient amount of time. Applying mild heat will accelerate cure time.   Let cool to room temperature.

7.  Demold the casting from mold - Lightly abrade casting with medium/fine steel wool until the desired metal shine and luster is attained. 

8.  Highlighting surface with dark brown shoe polish will give casting added depth and dimension.

9.  Patina effect can be achieved with patina paints available through Sur Fin Chemicals:  Tel. (323) 262-8108 (Super Antique 40, Berde, Rusty Brass, and Easy Brown)

10. To prevent oxidation of the metal, spray finished casting with two coats of clear gloss spray  (acrylic works well) available at most hardware/DIY stores.

* Recommended metal powder mesh size for mixing with resin is: -325 to -225. Metallic powders 
are available from Smooth-On and its distributors. Click on link at top of page or call our toll-
free hotline to find your nearest distributor.

** Use only a release agent specifically made for mold making and casting such as Universal Mold Release™ or Mann Ease Release 200™ (both available from Smooth-On and its distributors).

             Achieving a Cast Marble Effect Using Smooth-Cast 325™
                                            

 Overview – Creating a realistic cast marble effect is possible with Smooth-Cast 325 liquid plastic. Calcium carbonate (also known as “marble dust”) is mixed with SC 325 casting resin until the mixture is thick and creamy.  This mixture is then simultaneously cast with black pigmented  Smooth-Cast 325 to create the “veining” effect commonly found in marble.   Getting the effect you want will take practice and we offer the guidelines below as a step by step outline to get you started.

      Products Needed:     A. Calcium Carbonate (moisture free)     

                                            B.  Smooth-Cast 325 Casting Resin    

                                   C. Liquid Color Pigment (black & white) 

A.  Calcium Carbonate – Calcium  Carbonate (marble dust) should be completely free of moisture.  Calcium Carbonate is available from many Smooth-On distributors.  Call our technical help line to find your nearest distributor.

B.  Casting Resin -  Smooth-Cast 325 Colormatch is recommended because it is “color neutral” and readily accepts powders and/or pigments.  

C.  Liquid Pigment - Adding a pigment to the resin/calcium carbonate mixture will give the final casting added definition and dimension.

Also required: Rubber Mold; Mold Release Agent; measuring and mixing containers; mixing paddles; Gram scale or triple beam balance for weighing components.

     Amount of resin, calcium carbonate and pigment required will vary depending on the t    desired effect.  You will have to experiment by varying the amounts of resin, 
     calcium carbonate and pigment used in combination to attain an effect that suits
     your application. This example, we will use the following proportions:

     Part B of SC 325 Resin:  100 Parts  Calcium Carbonate:  100 Parts

     Part A of SC 325 Resin:  100 Parts  Liquid Pigment:   Black & White (1/2 Part Each)

     Measuring can be done by volume.  Greater accuracy is achieved with a gram scale.

1.  Apply Release Agent to Rubber Mold** - If casting into a urethane rubber mold, prevent resin mixture from sticking to rubber mold with application of a spray mold release agent (Smooth-On Universal Mold Release™) into mold cavity and all surfaces that will contact the resin. Brush lightly and follow with second light mist coating.  Let dry for 20 minutes.

       Create Calcium Carbonate Pre-Mix - mix calcium carbonate thoroughly with Part B of SC 325 (Blue Label).  Dispense 100 Parts of Part B into clean mixing container.  Add 100 Parts of calcium carbonate and mix thoroughly.  The consistency of the mixture will be very thick.

3.  Create White Pigmented ‘Part A’ Pre-Mix – Dispense 100 parts of Smooth-Cast 325 Part A into mixing container and add ½ part of white pigment.  Mix thoroughly. 

4.  Create A Black Color Concentrate For Veins – Dispense ½ part of Smooth-Cast 325 Part B into a separate mixing container.  Add ½ part of black liquid color dispersion. Mix thoroughly.  This color concentrate will be added to the calcium carbonate mixture prior to pouring.

       Combine Part A (with pigment) & Part B (with calcium carbonate and mix   thoroughly.

6.  Pour Mixture While Adding Pigment - Slowly pour the SC325/calcium carbonate mixture into mold cavity.  At the same time, pouring the black pigmented resine.  This dual pouring technique will create the swirl or “veining” effect that is commonly found in marble.   As we said earlier, achieving an acceptable veining effect may take some practice.

7.  Allow Casting To Cure Before Demolding - Remember: the resin/calcium carbonate mixture or filled resin will take longer to harden than unfilled resin.  Cure time depends on size of casting, mold configuration, amount of fillers used, etc.  Generally 30 to 40 minutes is a sufficient amount of time.  Applying mild heat will accelerate cure time. Let cool to room temperature

8.  Demold the casting from mold - Lightly polish casting with a wax until the desired luster is attained. 

** Use only a release agent specifically made for mold making and casting such as Universal Mold Release™ or Mann Ease Release 200™ (both available from Smooth-On and its distributors).

Smooth-On liquid rubber, liquid plastic and castable epoxy products are commonly used by artists and movie professionals to create an endless variety of special effects. Movies such as Jurassic Park, Free Willy, E.T., Star Wars, Ghostbusters, Star Trek Series, etc. have all used Smooth-On Products to turn ideas into vivid reality. These effects are achieved by adding various fillers (see technical bulletin on adding fillers or metal powders), color pigment dispersions and also by painting the cast pieces.

Pigmenting
We manufacture most liquid rubber and liquid plastic materials neutral in color so that they can be pigmented using So-Strong™ color Tints. Urethane Rubber products like PMC-724, PMC-744, PMC-746, and the 121 Series as well as plastic (and epoxy) products such as The Smooth-Cast ColorMatch™ Series, SC 320 and 20-136 readily accept pigments for color effects.

Smooth-On offers concentrated So-Strong™ Color Tints  in a non-reactive carrier that are compatible with most Smooth-On urethane rubbers and plastics. Pigments are packed in 2 oz. containers and available colors are Red, Black, Brown, Orange, Yellow, Green, Violet and Blue. Note: Avoid powder pigments or pigments dispersed in oils, resins, polyols or water because they may add moisture to your mix (foaming) or cause cure inhibition of the rubber or plastic product.

A small amount of pigment goes a long way. As little as 0.2 parts per 100 parts (of the Part B) may produce the desired effect while as much as 3 parts per 100 parts (of the Part B) can be added without significant effect on the Smooth-On product. Some experimentation on the part of the user is necessary to achieve desired effect. More than 3 parts dispersion may result in softening or oily exudation of the cured product.

Pre-mix the pigment into Part B (Yellow Label) of the Smooth-On product before adding Part A (Blue Label).

Painting A Cast Plastic/Epoxy Piece or Figure
Castings made with Smooth-On liquid plastic or epoxy products can be painted after being removed from a rubber mold. For best results, the release agent used (if any) to release the plastic from the rubber mold should be removed from piece with a strong detergent (dishwashing detergent) or solvent (acetone, mineral spirits or toluene).

Tip: Minimize Post Production Clean Up By Coating Your Mold With ATH…
Prior to casting plastic into the mold, Mann’s Ease Release 200 is applied to the mold followed by a powder coating of ATH (aluminum trihydrate). An air hose is used to blow any excess powder from the mold. The liquid plastic is then cast into the mold and allowed to cure. Once the plastic has fully cured it can be removed from the mold.
The casting comes out of the mold perfectly dry with a matte finish. An auto body primer is applied, followed by an acrylic paint and finally an acrylic sealer. The major advantage to powder coating is that there is no release agent to remove when the casting comes out of the mold.

Painting Your Cast Piece . . .
Our customers use a variety of paint products to paint their models. "Railroad Model Paint" (available at hobby/model stores) can usually be applied without a primer coat. If using acrylic or similar paint product, a primer coat may be necessary. Apply a base coat of auto body primer (available at most auto supply stores) evenly over the model surface. Let dry. Apply a second coat of primer if necessary.

After primer has dried, paint can be applied.

Achieving a Woodgrain Finish Effect

A wood grain finish can be attained by mixing urethane resin with various colors of pigment and Ure-Fil™ 5 filler.   Finished castings will have the appearance of natural wood.  Different wood finishes such as oak, pine, maple and mahogany can be achieved by varying the color and amount of pigment and/or Ure-Fil™ 5. 

Castings can be stained and finished by spraying with a clear coating.  Duplicating wood pieces with the following casting method offers the benefits of being fast, realistic and less expensive (labor, time, materials) than hand carving.

Overview - A rubber mold (negative) must be made of a natural piece of wood to capture the wood grain.    The liquid rubber (Mold Max™ 30 Silicone or  ReoFlex™ 30 Dry Urethane) will duplicate the finest wood grain and yield that detail into finished castings.  For information on general mold making, visit www.smooth-on.com.   Once a working mold has been completed, we can begin preparing our casting resin mixture.  This mixture consists of urethane resin, pigment and/or Ure-Fil™ 5. Once the desired color effect is achieved, the mixture can be poured into the mold.  In less than one hour the casting may be removed from the rubber mold.

Materials Needed:      

A. Smooth-Cast™ 320 Casting Resin         B. SO-Strong Brown Tint*           
C. Ure-Fil™ 5                                                     D.  Universal™  Mold Release

Our Smooth-Cast™ 320 Urethane Resin works well because it is inexpensive, has extremely low viscosity (pours like water), and sets up quickly.  Adding a dark pigment (brown or dark brown) to the resin/Ure-Fil™ 5 mixture will give the final casting added definition and dimension. If casting into a urethane mold, a mold release agent is required.  Other items that are needed include the rubber mold, measuring / mixing containers, mixing paddles and an accurate gram scale for weighing components.

Amounts of resin, Ure-Fil™ 5 and pigment required will vary depending on the desired effect.  Most customers will experiment by varying the amounts of resin, Ure-Fil™ 5 and pigment used in combination to attain a desired effect.   For this example, we will use the following:

Part A of Resin:  100 Parts          Ure-Fil™ 5: 100 Parts
Part B of Resin:  100 Parts          Liquid Pigment (Brown):  1 Part

1.  Apply Release Agent To Rubber Mold** - If using urethane rubber, you must apply a release agent to the mold cavity to prevent resin mixture from sticking to rubber mold.  Brush into all surface detail let dry and follow with a second coat.  Let dry.

2. Mix Ure-Fil™ 5 And Pigment With Part B Of Resin – If using Ure-Fil™ 5 in the urethane resin, it is necessary to bake the Ure-Fil™ 5 (150° F for at least three hours) to eliminate any residual moisture. Let Ure-Fil™ 5 cool to room temp. before using.  To allow ample mixing time, mix Ure-Fil™ 5 and color tint thoroughly with Part B of Smooth-Cast™ 320 (Blue Label) prior to adding Part A (Yellow Label).  Dispense 100 parts of Resin - Part B into clean mixing container.  Add 100 parts of Ure-Fil™ 5 and 10 parts of brown pigment to Part B and mix thoroughly.  Mixture will be very thick.

3. Add 100 Parts Resin - Part A to the Part B/Ure-Fil™ 5/pigment mixture and mix thoroughly.  

4. Pour Mixture into the mold cavity.  For best results, pour the mixture in a single spot at the lowest point of the mold.  Let the resin seek its level inside the mold.  A uniform flow will help minimize entrapped air.

5. Entire casting should be thoroughly cured before demolding. Remember, the resin/Ure-Fil™ 5 mixture or filled resin will take longer to harden than unfilled resin.  Cure time depends on size of casting, mold configuration, amount of fillers used, etc. Generally, 30 to 40 minutes is sufficient.  Applying mild heat will accelerate cure time.  Let cool to room temperature.

6. Demold - remove casting from mold. 

7.  Post Finish – Remove release agent from casting with Cascade dish washing gel & water or acetone.  Dry the casting.  Next, lightly abrade casting with fine steel wool to promote better surface adhesion of stain and shellac.  Apply desired wood stain or brown shoe polish thinned with alcohol onto the surface of your finished casting.  Let this coat dry thoroughly and apply a second coat.  After drying, apply two coats of clear gloss shellac spray to prevent scratches or nicks on the surface of the casting.

*Liquid tint used for this illustration is Smooth-On SO-Strong Brown Tint.  Using other pigments may vary results.  Some experimentation may be required.

**Use only a release agent specifically made for mold making and casting such as Universal™ Mold Release or Mann Ease Release™ 200 (both available from Smooth-On and its distributors).

For technical help or to find your nearest distributor:
Telephone: (800) 762-0744 • (610) 252-5800 • Fax: (610) 252-6200