Molding And Casting Rocks

My last post dealt with creating rocks by hand modeling. So this time I thought I'd touch on a couple ways of making rocks by casting them from molds.

Sometimes while walking the beach I'll find a rock or small piece of driftwood that calls to me. I don't know where I'll use it but if it is the perfect scale for using in a sculpture I'll hang onto it.

On occasion I'll make a mold of these found rocks. The rock I'm holding in the photo had barnacles adhering to it which I thought would make an interesting addition to a marine diorama.

Generally the materials I'll use for simple molds are liquid latex or 100% clear silicone caulk. For my mold separator I take a glass baby food jar and put a blob of Vaseline petroleum jelly in it.

To this I add a few drops of Naphtha. I keep adding the fluid and stirring the mixture till the Vaseline is thinned down to a brushable consistency.

If the model isn't too intricate another economical separator to use is neutral colored shoe polish. You apply it to your model and then buff it with a soft cloth.

On rocks I stick with the Vaseline mixture and just take an old bristle brush and apply it directly to my model.

After the separator I brush on multiple coats of liquid latex. Usually about 8 coats though that can vary due to the size of the mold. When the latex has cured I apply a bit of my separator to the outer surface of the mold and make a mother mold which will support my flexible latex mold. Sometimes on small molds I'll use Apoxie clay to make my mother mold. On larger molds I'll use Bondo Auto body filler.

Once the mother mold has hardened it is removed and the latex mold peeled away from the model.

The above photo shows a latex mold of the rock and its two piece mother mold. The rock was cast using a mixture of casting resin and Bondo auto filler.

The yellowish casting in my hand was made using Polytranspar Liqua-Cast from Wasco: WASCO -- Wildlife Artist Supply Company

When I don't have time for the multiple coats required for building up a latex mold I'll use 100% clear silicone caulk.

I'll use the same Vaseline mold separator on my model and apply a small amount of the silicone with a caulking gun.

Using a disposable brush I smooth the silicone over my rock model. Because the silicone is so thick this technique doesn't work well on highly intricate models. But for this river rock it worked fine. I try to get an even application of about a 1/4" thick.

The mold I'm holding is made of silicone caulk with a two piece mother mold of Bondo Auto filler.

When it comes time to cast the molds I'll brush a bit of separator in and use Apoxie Sculpt clay pressed carefully into the mold.

Other times I'll cast a mixture of casting resin/Bondo into the mold to make my rock. This is a picture of a small latex press mold and my cast rock.

In the photo below the lighter colored rock is Apoxie Sculpt while the darker one was made by pressing stoneware clay into the river rock mold. The size difference in the rocks is caused by shrinkage during the firing process.

Another option when it comes to making molds is to use the type of materials offered by companies such as Smooth-On - Mold Making and Casting Materials for a World of Applications!

The photo below shows a mold of the same barncle covered rock made using Smooth-On rubber in a plastic container in one pour.

After it cured the mold was partially cut apart to free the model. This method leaves much less seam line to clean off your casting then a traditional two piece mold would.

Creating Water Effects With Resin

I'm in the process of designing a sculpture which will have either a water dragon or sea serpent as its subject. With the last serpent I created I used Apoxie Sculpt clay to model waves around the creature.

Another method of creating realistic looking water effects is to use clear resin. I first used resin on a project in the early 1990's. That sculpture depicted two men hauling a net full of mackerel into their dory. Unbeknownst to them a Mako shark had been zeroing in on that school of mackerel and breached right next to their boat.

The creation of that sculpture was detailed in an article I wrote about sculpting and mold making titled Mako Antics for issue 32 of Breakthrough Magazine Spring 1993 . The resin I used for that project is Polytranspar Artificial water distributed by Wildlife Artist Supply Company.

Unfortunately I don't have digital pictures to share of Mako Antics but here is a photo of a recent sculpture I did where I used similar techniques to create the resin water.

If you are familiar with the film The Old Man And The Sea you may remember this scene where Santiago is bringing in his catch lashed to his skiff.

This piece required sculpting clay waves around the skiff and Marlin. Making a rubber mold of the water. And casting tinted resin in the mold to get my resin waves.

Another product I find useful for creating water effects is Envirotex. If you've ever been in a pub and seen a coin embedded on the table top under a clear coat of material likely it was EnviroTex!

I prefer using it over resin to create still water. It doesn't give off the awful fumes that resin does. Another advantage over resin is the surface dries completely tack free.

In this sculpture of a Gorgosaurus coming upon a dead dinosaur in a burned out section of the forest I used EnviroTex to make the water in the shallow creek.

In the close up photo you can see the stones and moss that line the creek bed. After gluing everything in place I drizzled a thin layer of EnviroTex over it. When it cured I poured subsequent layers till I achieved the depth I wanted.

If you've ever wanted to add water effects to your work using resin I'd encourage you to go for it. Just be sure to follow proper safety precautions in using it. And expect to go through some trial and error experimentation before using it on anything important!

One tip I would pass along is to keep a work journal and detail everything. And I mean everything! Right down to the temperature and humidity on the day you make your resin pours. You'd be surprised how it can effect how the resin behaves.

And I can't stress enough to test the compatibility of everything that is going to come in contact with the resin. It can be nasty stuff and attack certain materials

I'd also advise you to keep a dated record of the age of your resin. It definitely has a short shelf life. For that reason I always make a point of mixing up a small test batch before adding it to my project. Trust me you don't want the hassle of trying to remove uncured resin from your project!

A Tongue for the Styracosaurus

In his film Kessler wanted the downed Styracosaur to have its tongue ripped out by attacking raptors. This would require a flexible tongue, jaw and neck area.

I began by sculpting the tongue out of Super Sculpey polymer clay. Next I made a two piece Plaster of Paris mold of the tongue. Several days later when the plaster had dried I was ready to cast the flexible tongue.

I chose latex from the Monster Makers . They carry a high quality latex used for mask making. I mixed a small amount of latex with acrylic paint till I had a suitable fleshy tone. I brushed two light coats of this latex/paint mixture inside my mold. When it dried I clamped my mold halves together and carefully inserted a braided section of aluminum wire down the center. I then filled the rest of the mold with pure untinted latex. When the latex dried a few days later I had my flexible tongue.

Casting Kong's Head

After I finished building up the latex rubber mold to about an 1/8" thick I made a mother mold. A mother mold is made of a rigid material and supports the flexible latex mold while it is being cast to prevent distortion. For this piece I used plaster of Paris and strips of burlap to make the mother mold.

The casting material I used is called Polytranspar Liquid Cast. It is a two component product which requires mixing together equal amounts of Part A and Part B. The reason I like it is because it sets up within 3 minutes, has little odor and can be removed from the mold in a short time.

I sprayed the inside of the two mold halves with a light coat of mold release and clamped the mold together. After mixing the Polytranspar liquid cast I slowly poured it into the mold trying to avoid causing air bubbles. When I had poured about 8 oz. into the mold I began to rotate the mold by hand to make sure all the surfaces of the mold were evenly covered. I continued doing this for several minutes till the material set up.

Here is a picture of Kong's head fresh from the mold and ready to be cleaned of the flashing left on the casting from the mold seam. Next post I'll get down to installing some teeth in Kong.