Mold Making Tutorial: Silicone Mold of Clay Sculpture

Clay sculpture for mold is very important of the figure .today we talk about the detailed sculpture casting process and the mold making.

Make a conclusion about the process ,it is like the below .

Step 1: Select a Mold Making Method & Mold Rubber
Step 2: Construct Mold Box & Prepare Sculpture
Step 3: Measure, Mix & Pour Silicone Mold Rubber
Step 4: Demold
Step 5: Cut the Mold

Step 6: Rotational Casting

 Step 1: Select a Mold Making Method & Mold Rubber

Mold Making Method

For this sculpture, we select the “poured block mold” method.

Here are the reasons that we are eliminating other methods:

Brush-on Mold: We are concerned that air bubbles may form in the intricate details on the base of the sculpture. Also, brush-on molds tend to have thick and thin spots – thin spots end up being weak points in the mold.

Poured Blanket Mold: One of the steps in the poured blanket mold process is to form a layer of clay on top of the original model (review a poured blanket mold tutorial here). This step would most likely deform the clay original.

Based on the shape of the sculpture, we also know that the mold will require a cut in order to remove the original sculpture and subsequent castings.

 Mold Rubber

For this particular project, we also know that we want to use a silicone mold rubber because it does not require release agent when casting polyurethane resin. Release agent can be difficult to apply in intricate areas and it may be difficult to remove from the casting. Residual release agent can prevent paint from sticking to castings.

Platinum-Cured vs. Tin-Cured Silicone Rubbers

Polytek silicone falls into two general categories: platinum-cured and tin-cured.

Step 2: Construct Mold Box & Prepare Sculpture

To begin, a plywood mold box is constructed at the proper dimensions (i.e., at least 1″ beyond the sculpture in all directions) and then sealed with petroleum jelly.

NOTE: It is a good idea to taper the inside of the mold box so the mold can be removed more easily when the mold box is turned upside-down.

Based on the new dimensions of the mold box, we determine that approxi ents are measured by weight and then mixed thoroughly.

NOTE: Do not attempt to measure products with 1A:10B mix ratios by volume – always measure by weight.Because of the quantity of rubber needed for this project, we mix two separate batches using a turbo mixer.The rubber is mixed until a uniform color is reached.

NOTE: Avoid hitting the sides of the mixing pail with the turbo mixer as this can introduce air into the mixture.The batches are then mixed by hand with a Poly Paddle.

 NOTE: It is important to scrape the sides and bottom of the mixing container several times, as this is where unmixed material tends to cling.The silicone is poured into the lowest point of the mold box and allowed to rise.

The rubber is poured until it reaches at least 1.0″ above the highest point on the sculpture.We allow the rubber to cure at room temperature for ~24 hours. Heat lamps can help speed the cure.

NOTE: Demold times vary by product. Check product Technical Bulletins for this information.

Step 4: Demold

Before demolding, the locations of the mold box walls and block-outs are marked with a pen. This is done so that the mold box can be put back together correctly for casting later.All mold box walls and block-outs are carefully removed.All edges of the mold are loosened from the baseboard with a putty knife before the entire mold is removed.Upon removal of the mold from the baseboard, the sculpture splits in half, leaving the top half in the mold.

Step 5: Cut the Mold

To remove the remainder of the sculpture and subsequent castings, we prepare to make a cut on one side of the mold. Pictures of the sculpture are printed to determine a good location for the cut.

NOTE: If possible, it is best to cut along a line that already exists on the sculpture or in an inconspicuous location (i.e. avoid the face).

 Step 6: Rotational Casting

The mold is placed back into the mold box and then secured.the mold is removed from the rotational casting machine and then the casting is removed from the mold.For the next run, we mix EasyFlo 120 + Brown PolyColor Dye + Bronze Powder to produce a cold cast bronze copy.Hollow castings such as these can be backfilled with a number of products, including less expensive resin or polyurethane foam.