Introduction

Ready to Begin!
The following 5-step instructions will guide you step-by-step through the mold-making process:

DO NOT cut the mold all the way around.  Cut it just far enough to slip the part out. A mold cut in this manner is referred to as a "cut mold", "split mold" or "glove mold".

Using the glue of your choice, attach a 1/4" thick wooden dowel rod to your object.  The dowel must be long enough to extend out of the containment cup when the object connected to it is suspended mid-way in the cup.

STEP 3:  FASHION AND PREPARE AN ARMATURE

Next, rig a stand to hold the dowel with the attached object suspended in the center of the cup.  This stand can be something as simple as a bent-up wire coat hanger duct taped to the dowel.  You can also drill a hole in the dowel to slide a smaller dowel or wire crossbeam through it, resting on the lip of the cup. A simpler option may be to glue the dowel (at a shorter length) to the base of the cup, holding the piece suspended upright  (not pictured).

I use a homemade wooden stand (shaped like a Stonehenge formation with a hole in the center crossbeam for the dowel).

On the dowel, mark a perpendicular line about 1/4" away from the attached object.  This will serve as your "pour-to" depth line.

Also, mark a vertical line on both sides of the part.  This will be your "cut" line, where the mold will have a seam.

STEP 4:  POUR YOUR MOLD

Now you're ready to mix the liquid rubber compound and pour your mold!  Follow the "Shake Well" instructions on the bottle(s) and grab two more plastic cups identical to your containment cup.

Any way you build it, the armature's purpose is to ensure that the object does not touch the sides of the containment cup and hold it from floating around when the liquid rubber is poured.

Since wood is a porous material, you'll have to coat the dowel with the SuperSeal sealer included in the mold-making starter kit.  If your prototype part is made out of an air-drying clay, it too is pourous and must be sealed.  Next, coat both the prototype part and the dowel with the universal mold release agent.  This is important, as without the mold release, the mold would fuse to your part and separating the two would destroy the mold itself. When applying both the the SuperSeal and Universal Mold Release agents, DO NOT use the spray pump that comes with them, as the spray is very ineffective and wasteful.  Instead, using a soft-bristle paint brush, GENEROUSLY brush the agent onto the part you are going to put into the molding rubber.  Make sure that the entire surface of the part gets good coverage.

Pour some of the release agent into one of the 7-ounce plastic cups--enough ONLY to cover the botom of the cup*.  Roll the cup around so that the release agent coats the entire inside of the cup. This cup will be your "containment box" into which the mold is poured.  I recommend using disposable plastic cups, as they are non-porous, flexible and of course... disposable.  Get the transparent kind so that you can measure through them easily (the red or blue translucent 'party' cups work great because they're sturdy too).

When the cup is completely coated, pour any excess release agent back in its bottle and replace the cap as it evaporates quickly. Set the containment cup aside for now and allow the the mold release coating to dry (about 5 minutes).

STEP 1:  PREPARE THE MOLD-CONTAINER *Step 1 is not necessary when using silicone-based rubber such as Oomoo.

The two-part mold-making rubber is a 1 to 1 mix ratio, so pour equal amounts of  parts  A & B  into  each  of  the  two cups.  Pour  enough  of  each  so that, when  combined  and  poured  into the containment cup,  the total amount will completely submerge the part you are casting.

Take your time to measure carefully for a good mold--compare the cups side-by-side.

When you have measured equal parts, mix parts A & B together in one cup.

Finally, pour the rubber down the side of the containment cup so it fills the space underneath the part.  Continue pouring slowly until the liquid completely covers the part by at least 1/4" (your line marked on the dowel).  To reduce the occurrence of bubbles in the mold, pour a THIN stream of liquid VERY SLOWLY.   The dowel that is left sticking out of the rubber will serve as your plastic pour hole later.

Using a plastic fork, stir thoroughly. Three to five minutes of stirring is usually enough when using Oomoo 25. Remember, it's "pot life" is only 15 minutes! After that, it begins to cure.

The Oomoo 25 rubber cures in 75 minutes. Let it set firmly... this takes patience, but a well-cured mold is very important.

Once the rubber has cured, work the mold out of its containment cup. It is likely that you will need to cut the cup away from the mold.

Slit down to the part inside.

Using a hobby knife, slit the rubber mold along the "cut" lines on both sides of the dowel.

On the dowel, locate the "cut" lines (from STEP 3).

If you used a liquid mold release, its residue may leave your original part feeling slippery. You can rinse the residue away with tap water.

Now you have a finished rubber mold -- an exact inverse or negative of your original part. This mold is what you will use to create duplicates of your original part.   The mold is reusable, and if used with care, will last through many plastic castings.

SAFETY FIRST!!! Mold-making & casting can be a fun hobby, but remember that you are working with chemicals.  Please take the time to read all MSDS (Material Safety Data Sheet) information provided by the product manufacturer and take all possible safety precautions.

Mold-Making

Painting & Finishing

STEP 2:  PREPARE THE PROTOTYPE PART

*Do not pour an exessive amount of release into the cup or let it sit too long before pouring the liquid out of the cup----the release would eventually eat through the plastic cup.

* NOTE:  The following steps were performed using Smooth-on's Evergreen20 mold rubber.                 The colors will differ from that of an Oomoo mold, but the procedure is identical.

Again, the color of your mold depends on which rubber product you are using.

Example of Evergreen 20 mold color.

This tutorial describes the moldmaking process using products from Smooth-On, a company specializing in liquid rubbers, plastics & foams since 1895. Their products are widely used for in the film industry, architecture, and doubtless by many a toy customizer such as yourself! Their products are available to order online at www.smooth-on.com where you can also look up local distributors.
For first-timers, Smooth-On offers a discounted starter kit (see item #8 above), complete with everything you'll need to make molds AND to cast resin plastic parts. The discounted kit is only available once per customer (after that, you have to order each item individually at its full price) and contains the following:
- Oomoo 25 liquid mold-making rubber
- Smooth-Cast 300 liquid plastic resin for casting
- Ease Release 205 mold release agent *contrary to Smooth-On's instructions, I have found that mold release is not necessary when using silicone-based rubber such as Oomoo.
- SuperSeal sealer for pourous surfaces
- "How-to" materials

STEP 5:  DEMOLD THE ORIGINAL PIECE  (Prepare your mold for plastic castings)

Example of Reoflex mold color.

Customizer's Start-to-Finish Tutorial Guide:

Plastic Casting

Sculpting