Now, one of the things that was the least stressful for me, stone molds. The basics of making a mold (no undercuts, mold line, the dreaded clay wall…) are covered in the fiberglass mold tutorial, so check that out first, I’m just sticking to what makes a good stone mold in this.
As with the fiberglass molds, make sure there is a key in the stone part of the mold, to help line up the mold with the inner piece when you’re casting. Put a layer of clay covered with saran wrap under your sculpture so that the details aren’t ruined by laying on the table, and make sure to mark out your mold line with a sharpie.
Cover the clay with a few layers of Krylon Crystal Clear- stone isn’t as sensitive to moisture as fiberglass is, but still use at least 4 layers if you’re using WED clay, and two or three if you’re using oil clay. Next, spray it with a layer of Krylon Dulling Spray- you can find this at art stores- to help keep the ultracal from sliding down and not sticking to the sculpture.
Start building a wall, and make sure to put a vertical wall at the top of your sculpture if it’s cut off like ours, as you can see in the above picture.
Also put a vertical wall, 2-3 inches thick, all around your clay wall. Another very important thing, KEYS. We totally did our keys wrong in our first stone mold. We made the edges of the keys 90 degrees, where they should have been slanted so that there was absolutely no chance of there being any undercuts. We did have some keys break off in our first mold, but it still fit together perfectly, and still baked just fine, just made for a bit of a headache when they were falling off.
Important! If you have any exposed stone at ALL, rub that stuff down with some vaseline, otherwise you aren’t going to get that mold apart.
After the clay wall is done and the keys put in, spray the clay again with some Crystal Clear and dulling spray, and we’re ready to start with the stone.
We used Ultracal 30, and followed a tutorial from the book I can’t talk enough about, Special Makeup Effects for Stage and Screen. Seriously, you guys would learn way more from this book than I could ever put into a tutorial.
The book says to do a thin detail coat first, mixing up a small amount of ultracal into a ‘thin milkshake consistency’. In case you’re wondering about what a thin milkshake looks like, pretty much it’s just not so thin that it’s watery, but not so thick that it doesn’t pour easily. Pretty much what it looks like in the picture. Take a chip brush, and gently cover the sculpture with about a 1/4 inch thick layer of the thin ultracal. Wait about half an hour and let it set up, cutting up small pieces of burlap while you’re waiting, and then mix up a larger batch of ultracal (it takes some time to learn exactly how much for each side you’ll need, I think we ended up mixing up more a few times while we were learning). Also, WEAR GLOVES when working with this with your hands, it will dry out your hands and also it’s very bad for your skin.
This part is easiest with two people, but you can still do it with one. Dip the pieces of burlap into the ultracal, and make sure they’re thoroughly saturated. Then, carefully place one piece at a time over the first layer of ultracal, gently using a brush and your fingers to make sure there are no air bubbles! This is very important, air bubbles are bad because you will get holes in that first layer if you aren’t careful. Continue covering in burlap until you get 4-5 layers.
Let this set up maybe an hour, just until it’s set, and then go on to the ‘beauty layer’. This layer just makes the mold easier to hold on to, strap together, and stronger.
Mix up a slightly thicker (think, milkshake that is easy to drink through a straw, but not thin at all) batch of ultracal. You may need to wait a bit for it to thicken more to work with it, and cover the entire sculpture with it, slowly smoothing it out with a kidney tool that you’d use to smooth clay, until it’s nice and smooth.
The top coat should look like this. You can take a rasp and clean up the edges later, after you do the other side.
I think it’s pretty important to let the stone harden enough for you to be able to handle it, I like to wait at least three hours before doing the other side of the mold.
Flip the mold over, and start to gently remove the clay. If you did a good job on releasing it, you should be able to remove the clay easily. If not, water and a soft brush should help.
After you’ve removed the clay, build another 2-4 inch thick vertical wall around the other half of the stone mold, and put in-this is very important- pry points. These are little holes that will be in the mold along the mold line that help you to open the mold. We did not do these on our first foot mold, but luckily the broken out keys helped us to open it up. Just make little rectangles of clay, just thick enough to get a screwdriver into, and press them along the edge of the wall, as you can see above. The pry points are those little square pieces you see. Make sure to put a pry point at the top of your stone middle piece, too! It makes it a lot easier to take out.
Again, spray all clay with Crystal Clear and dulling spray, and don’t forget to release all stone with vaseline! Get it down into the keys, too.
Now repeat the three layers from the other side, the detail layer, burlap layer, and beauty layer. I like to let the finished mold sit overnight to fully dry out and strengthen before I try and open it.
To open the mold, taking your time is the most important thing. If you try and rush it, you will end up cracking or breaking the mold, and having to start all over, possibly with having to resculpt your piece as well. Remove the clay wall if you haven’t already, and gently insert a screwdriver into the pry points you made, while carefully wiggling the screwdriver until there is an opening large enough to stick a popsicle stick into. This is easier with two people, but you could do it alone if you wanted. Work your way all the way around the mold, gradually stacking popsicle sticks until the mold pops open.
Most likely, your middle piece is still stuck in there, and if you put in a pry point, you should be able to carefully loosen the top part, but you may have to remove some clay to get the rest of it loose to take it out. Make sure to take it slow and be careful! Try to save the clay you take off the stone that you used to sculpt it, so you can measure it and figure out how much foam latex you’ll need, if you’re using foam latex.
After that, all that’s left is to clean it out, and I find D-Limonene works really well if you use it with a chip brush. Make sure to store your molds strapped together!
We did our two feet molds and the head and face mold in stone. The face mold was done as a one part mold, so you’d lay it down on a smooth surface that the stone wouldn’t stick to, and do your three layers just as we did before. The head mold was three pieces, which is a bit more difficult than two, but it’s all about putting your mold lines in the right places.
Thanks for reading, next post is on the wings! How exciting, right? It might take two weeks to get that one up since I’ll need Mario’s help on it, he did design them, so we’ll see. Happy crafting!