Introduction: Seaming and Patching Silicone Puppets


For those interested in stop motion animation and puppet fabrication: This Instructable showcases a technique to get rid of the visible seam caused by casting a silicone puppet in a two-part mold. I have found very few online resources for this step in the puppet fabrication process. Through consulting with several stop motion industry professionals, and my own trial and error process, I have put together this demo to shed some light on this guarded stop motion secret.

There are so many great demonstrations of puppet mold-making and casting techniques online, so in my tutorial I will provide only a quick overveiw of my molding and casting process for context, and focus primarily on seaming and patching.



Two-part platinum cure silicone for mold (Ex. Smooth-on Smooth Sil 945)

Two-part platinum cure silicone for cast (Ex. Smooth-on Dragonskin 20)

Silicone paint for tinting cast (Ex. Smooth-on Silc Pig)

Sulphur free clay (Ex. Protolina)

Mineral oil

Mixing cups

Stir sticks (Ex. Popsicle sticks)

Vacuum chamber and pump for degassing silicone (or find a low viscosity silicone that doesn't require degassing)

Wax-based mold release (Ex. Ease Release 200)

Mold wall material (Ex. Lego blocks / foam core / cardboard)

Fine cuticle scissors

Rotary tool

Aluminum oxide fine grit grinding stone

Petroleum jelly

Silicone caulking (Ex. GE All Purpose Silicone I Clear Window and Door Caulk)

Silicone solvent (Ex. Dow Corning OS-20 / Naphtha)

Fine-tipped brushes

Matting powder (Ex. Powdered sugar)

Well-ventilated workspace

Step 1: Prepare Your Model/Sculpt for Casting

As I mentioned in the overview, I will be giving a cursory description of the mold-making process in order to focus on seaming and patching.

Once you have your sculpt/model, it's time to plan your two-part silicone mold. The female character for this demo is made out of Magi-sculpt, which is a two-part hardening resin. I like to make the original model out of a hard material in case I need to re-cast it for any reason. However, you can also make your sculpt out of plasticine and spray it with a protective coating of Krylon Crystal Clear.

Note: The general rule of mold-making is hard to soft and soft to hard. Because I have sculpted this model out of a hard material, I will be making the mold out of silicone, so that it releases easily and does not get snagged on undercuts when I de-mold it. If you make your model out of something soft, such as sulphur-free plasticine (sulphur in clay reacts badly with silicone), you can use Hydrocal plaster to make your mold (much more cost efficient). Just be aware that during the de-molding process your original model will most likely get destroyed.

Time to plan your seam. I've spray painted my sculpt in white and then taken a pencil and drawn a line around the halfway mark of the form, especially in between the fingers, trying to get as equal a volume on either side as possible.

The next step is to build up a bed of clay (sulphur-free scrap clay such as Protolina) up to the halfway mark of your seam. Take your time with this part of the process. You want to get as tidy a seam as possible so try and make the surface of the clay meet your model at a 90 degree angle. You can use mineral oil to smooth oil-based clays (see video). Use cotton swabs with mineral oil to clean your sculpt free of clay and smooth the edge where the clay meets your model.

To prepare for pouring the first half your mold, you'll want to make registration keys in the clay. You can use some sort of square object such as a square dowel to make these indentations. I like to make as many keys as possible to keep the mold firmly in its proper place and prevent any slippage during casting.

Step 2: Pouring the First Half of the Mold

Now you're ready to build the walls and pour the first half of your mold.

Note: Make sure you have a nice clean workspace. Keeping an organized work area is tantamount to successful mold-making - and to making most things (figure 2.1)!

You can build your mold walls out of a variety of materials. Lego blocks and foam core work well. For this project I used a combination of Lego blocks and cardboard. Build your walls around the bed of clay. In terms of height, I determined that 1.5 in of silicone would give me .5 in of thickness from the highest point of the model, so the walls needed to accommodate that much silicone. I then hot glued the walls in place and rolled pieces of Protolina clay to seal between the cracks in the walls and where the bed of clay met the wall (see video from Step 1).

To conserve silicone, you can determine the volume of your mold before mixing and pouring (see fig.. If it's a box shape mold, it's a simple formula of L x W x H. Since I was working with a trapezoidal shape in order to conserve silicone, I determined the volume by: L(the average of the top Length and bottom Length) x W x H. Math! Yikes! (figure 2.4)

Ready to mix and pour... I used Smooth-on's Smooth Sil 945, which is a very firm platinum cure silicone. It can be mixed by volume or weight. Through my calculations I determined I would need approximately 2000 g of silicone for the first half of the mold. Lucky for me this was about the exact amount of a trial sized batch of silicone from Smooth-on.

Mix the silicone by equal weight and then use a vacuum chamber and pump to degas the silicone, getting rid of as many bubbles as possible (see video).

Note: When the silicone is ready to be poured I like to take a small cotton swab and dribble some silicone over the more detailed parts of the mold, such as the eye sockets to ensure that the silicone reaches every corner and crevice without trapping any air.

Raising the bucket of silicone high above your model, start to pour a very thin line into the lowest part of your mold. Pouring from a great height in a very thin stream is another method of preventing air bubbles in your silicone. Slowly fill your mold up to the desired height and then let set overnight (figure 2.5).

Step 3: Pouring the Second Half of the Mold

Once the first half of your mold has fully cured, remove the mold walls and peel back the clay (figure 3.2). There will be some clay residue on the back half of the mold, which can be cleaned up with some mineral oil. When the mold and back half of the sculpt is clean, spray it thoroughly with a mold release such as Ease Release 200. Spray a preliminary coat, holding the can 12 in away from the mold. Then take a clean brush and brush the mold release into any crevices and corners, and then spray one more coat. Build up the walls again around the first mold half, repeating the process of filling the gaps with Protolina. The volume of silicone should be the same as the first batch. Mix another batch and repeat the process of degassing and pouring performed in step 2. Let cure overnight (figure 3.4).

Step 4: Casting Your Puppet and Setting Your Armature in the Mold

Time to de-mold your model/sculpt. Dismantle the mold walls and gentle peel apart the two parts of your mold. Gently pull your model/sculpt out, being careful around the undercuts so as not to tear the silicone. You can now clean the mold with cotton swabs and isopropyl alcohol.

Since silicone only sticks to silicone it's important to use a mold release again. Use the same method as was used in step 1. Spray a coat of mold release and then use a brush to make sure the mold release reaches every corner of the mold. Spray a second coat.

Now it's time to set the armature inside the mold and cast your puppet!

Note: This Instructable doesn't cover armature construction but there are many great tutorials for making wire armatures out there on the web.

I use a two stage casting process, which helps fix the armature in place so that none of the wires show through the silicone.

Part I: First Impression Beauty Coat

Mix a small batch of Dragonskin 20, which is mixed by equal volume or weight. Mix a tiny amount of Silc Pig coloring into the batch. De-gas silicone. There is a limited pot life, so the next step should be done with expedience but also caution. Dribble a line of silicone throughout the base of each half (figure 4.3). Using a cotton swab or brush, coat the mold with a thin layer of silicone, making sure you don't paint over the lip of the mold. This silicone layer will serve as a beauty coat and make sure that the coloring is cohesive and even. It will also ensure that the wires stay in the center of the mold. There is a 30 minute pot life, so I usually wait an hour to start the second part of the process; this will mean the beauty coat will be firm enough to hold the armature but still uncured enough to bond with the second batch of silicone.

Part II: Locking the Armature in Place and Casting the Remaining Silicone

To lock the armature in place, use the GE silicone caulking. Mix a tiny amount of Silc Pig coloring with a dab of silicone caulking. You can add a little solvent such as naphtha to the mix to make it a little more viscous. Make sure the wire armature fits correctly in the mold and then dab the caulking onto key parts of the armature, such as the back of the hands and neck, and then position it in the mold (figure 4.4). The caulking dries very quickly, so the armature will be locked in place within about ten minutes.

Mix a larger batch of silicone and tint it with the same ratio of Silc Pig as the first batch. Pour it slowly into each half of the mold. Make sure no air gets trapped underneath the armature, so go slowly and shake and tap the mold periodically to dislodge air bubbles. Fill the silicone to the top of each mold (figure 4.5). Let the bubbles rise to the surface for a few minutes and then join the two mold halves together.

Smooth Sil 945 is such a firm silicone that it can be weighted down heavily to create as thin a seam as possible. You may have to experiment with how much weight creates the thinnest seam, but too much weight can distort the cast. For two mold halves, both 1.5 inches thick, I used about 9 bricks to compress the two mold halves (figure 4.6 and 4.7). Let cure overnight.

Step 5: Trimming the Silicone Flashing

Gently peel apart the two parts of the mold. When you take your puppet cast out it will be circled by silicone flashing. Using cuticle scissors, trim the flashing as close to the base of the seam as possible. Be careful not to cut a trench however.

Step 6: Buffing and Grinding Down the Silicone Seam

When the silicone flashing is trimmed, it will still have a visible seam (figure 5.1). To get rid of this seam you can use a rotary tool with an aluminum oxide grinding stone to grind away the flashing.

Note: I was able to track down a fine grit aluminum oxide grinding stone online, which will make a difference. The reason aluminum oxide works well is that it is a composite of smooth round particles; jagged or sharp particles, such as silicon carbide grinding stones, will tear the silicone.

Grinding away the seam takes practice, so before jumping in, practice on a part of your puppet that will be hidden in the final version, either underneath clothing or hair.

Set your rotary tool to the highest setting. It's important to keep the silicone constantly lubricated with petroleum jelly. Take a dab of petroleum jelly and rub it into the seam at intervals, applying light pressure with the grinding stone in short, circular motions (see video). This process takes patience; going too fast or applying too much pressure can tear or dent the silicone.

The final result can be good enough for camera (Figure 5.3 and 5.4) but sometimes dings, dents and tears happen, or there might still be a slight crease remaining where the seam was. Step 6 goes over patching these imperfections.

Step 7: Patching Imperfections in Silicone

You can use the GE silicone to patch any imperfections. Mix the GE Silicone with a solvent (Dow Corning OS-20 or Naphtha will work). Add a dab of the Silc Pig coloring to match the color of the puppet's skin. The mixture should have a low viscosity to make it easier to blend.

Dab a small bit of the mixture over the imperfection. Using a small brush, dip it in solvent and use the solvent to blend and fade the edges of the patch (see video). The silicone caulking dries quickly, so you can only patch small segments at a time.

Above you can see before and after photos. Figure 7.2 shows a slight crease. Figures 7.3 and 7.4 show the crease is gone after being patched. Figure 7.5 shows a hole in the nose caused by an air bubble during casting. Figures 7.6-7.9 shows the nose after being patched.

This technique also requires some patience and practice, so be prepared to spend some time practicing before you get the results you want.

After patching, it's time to matte the silicone!

Step 8: Matting Silicone

As soon as you've patched the silicone, it's time to use a matting powder, otherwise the silicone will be glossy when it dries. There are silicone matting powders on the market, such as the one made by FuseFX, however, I've had good success with powdered sugar.

Dip a brush into a bag of powdered sugar and blow the powder onto the silicone (see video). Make sure it's thickly coated (figure 8.2).

Now your puppet has a clean skin surface on which to paint and add details!

This Instructable ends here but perhaps in the future I will post a demonstration of silicone painting. To see these puppets in different stages of development you can check out my instagram page: @blakedouglasyoung

Happy fabricating!