How to Make Resin Castings

Casting, or the act of making positive copies from the negative impression left in a mold, is often done in materials like latex, plaster and resin, all of which suit different purposes. Casting resin is usually polyester or polyurethane, the former of which is used in most figurine or prop casting, while the latter is most suitable for making dolls and other hollow toys. Learn how to use polyester resin to create a basic cast from a 2-part mold.

Things You'll Need

• Model object Latex gloves Safety goggles Protected workspace with forced ventilation Vapor respirator Stirring tools Plastic cups Silicone RTV rubber and catalyst Rubber bands Razor blade Polyester casting resin and catalyst Legos Modeling clay Small wooden craft balls Sandpaper Acrylic paints and brushes Polyvinyl alcohol

Instructions

Molding

1. Create a molding box for the object you want to copy. Build a square or rectangle of Legos that gives your object a clearance of at least 1/4 inch at the top, bottom and all sides. Roll out a length of modeling clay to use as the bottom of the box, and leave the top open. If you are making a large molding box, you will need to build it of wood instead.

2. Mix about half your silicone RTV rubber and catalyst together in a cup, following the mixing directions on your particular product's packaging. Pour the silicone rubber mixture into the molding box, stopping at the halfway point.

3. Press the model object into the rubber, until it is half-covered. Around the object, also press several wooden craft balls half into the rubber, to create keying depressions. Let the silicone rubber cure for 12 hours, or overnight.

4. Remove the wooden craft balls from the rubber. Mix together the rest of your silicone rubber and catalyst, and pour the mixture into the molding box, over the rest of the object. Fill the box completely, and let it cure for 12 hours.

5. Disassemble the molding box and pull the mold apart so that you have 2 halves. Remove the object from the mold, then place the halves back together and strap them in place with rubber bands. Cut a pouring hole into the bottom of the mold with a razor blade.

Casting

1. Prepare your casting area by covering all surfaces with plastic and increasing the ventilation in the room by opening doors and windows. Put on a vapor respirator, safety goggles and latex gloves, and keep a bottle of polyvinyl alcohol nearby to clean up any spills.

2. Mix together your polyester casting resin with its catalyst, following the mixing directions on your packaging. Make sure the mixture is free of air bubbles.

3. Pour the casting resin into the hole in the bottom of the mold, slowly to avoid air bubbles. Fill the mold completely, and let it cure for 5 to 12 hours. Curing time will depend on your particular brand of resin.

4. Remove the rubber bands from the rubber mold, and separate the mold halves. Pull the new resin copy of your object from the mold.

5. Sand the resin smooth by holding your new object underwater, so that the toxic dust does not get in your lungs and eyes. Paint and finish the figure as desired.

References

• The Prop Builder's Molding and Casting Handbook; Thurston James; 1990

Resources

• Alternate Casting Tutorial