You can buy a variety of molds for kiln casting (as well as other glassworking techniques). But maybe you want to save some money, expand your skills, or open up your creative options.

If so, making your own glass molds is a great way to advance all these goals. So let’s explore what it takes to make glass molds for kiln casting in this beginner’s guide.

The Possibilities of Kiln Casting

Image Source: Etsy: PuttinOnTheFrits

The kiln glass casting process involves placing glass pieces in a mold. Then you melt the glass pieces in a kiln. The molten material takes the shape of the mold.

As a result, you can make lots of different shapes including:

• Bowls
• Vases
• Sculptures
• Pendants
• Lots more

It all comes down to the shape of your mold. In this article, we’ll look at how to make three basic types: lost wax, open faced, and sand casting molds.

Making Lost Wax Casting Molds

You’ll sometimes see the lost wax method called “investment casting” or the French term, “cire perdue.” It’s a traditional technique for creating detailed glass sculptures, art pieces, and functional objects.

Lost wax casting involves creating a mold shell around a wax model. You melt the wax away in the kiln, leaving a cavity for the molten glass to fill.

Materials

• Modeling wax
• Refractory mold mix powder, such as Zircar Luminar Mold Mix 7
• Water
• Spatula and stick mixer for mixing
• Small brush
• Mold release agent, such as dish soap or silicone spray
• Acetylene torch

Steps

1. Create your wax model sculpture.
2. Mix water into the mold mix powder per the manufacturer’s instructions. For Mold Mix 7, it’s 4.8 pounds of water for the 1 gallon bucket.
3. Use a spatula and stick mixer to remove all clumps and make it smooth.
4. Apply a thin, even coat of mold mix with a small brush. Be sure to get into all the crevices and corners. Allow the first layer to dry.
5. Apply multiple coats, drying each time. With Mold Mix 7, aim for up to 1/8 inch thick (~8 coats). Other mixes may require greater thickness.
6. Let the mold dry for up to 48 hours.
7. Place the mold on a grate over a metal container. Use your torch to burn out the wax.
8. Your mold is now ready for casting!

Here’s a look at the process in action:

Making Open Faced Molds for Glass Casting

The glass casting process with an open-faced mold is straightforward. Once you’ve acquired or made your mold, you place your glass pieces inside. Then put the mold in the kiln. The glass becomes molten and takes the shape of the mold.

Open-faced molds often have a small cavity for shallow glass objects such as plates, trays, and bowls. But what you make comes down to the mold’s shape. You can build your mold around just about any shape when you make your own!

Materials

• Plaster
• Silica flour
• Water
• Containers for mixing the mold material and housing the mold as it dries
• Mold release, such as silicone spray
• N95 respirator for working with silica – breathing the dust is toxic!
• Small brush

Steps

1. Select or create the object on which you’ll base your mold. Apply mold release spray and let it dry.
2. Mix 1 part plaster and 1 part silica flour.
3. Add the dry mix to 1 part water all at once. Let it sit for 3 minutes as the water begins to absorb the mix.
4. Mix by hand for 2 minutes.
5. Apply a thin face coat to the mold base with a small brush. Be sure to push the mix into all the small details. NOTE: If you’re doing a simple plate without intricate details, you can skip this step.
6. Check if your mix is thickened to the consistency of whipped cream. That’s about what you need to keep the mix from running off your base.
7. If it’s ready, you can begin applying it by hand. Apply evenly to a thickness of 2 – 2.5 inches. Achieving this thickness may take a few layers.
8. Let the mold cure for up to an hour, then remove from your base. Allow it to dry for several days.
9. A final step that can strengthen your mold is called bisque firing. Place the mold in your kiln. Consult with your material supplier on the right bisque firing schedule. Here’s a general guideline:
1. Ramp up at 200 °F per hour to 1,100 °F.
2. Increase the ramp rate to 400 °F per hour up to 1,900 °F. Hold for 10 minutes.
3. Turn off the kiln and allow the mold to cool to room temperature.
10. Your mold is now ready to use!

Watch an expert demonstrate building an open-faced mold:

Making Molds for Glass Sand Casting

Sand casting is a classic hot glass technique. There’s a key difference from the two methods we’ve already discussed.

In this case, you’re completely melting glass pieces into a liquid—requiring at a higher temperature than other casting methods. Then you remove the liquid from the furnace and pour it into the mold to harden.

The sand casting process is often used for larger-scale projects and art installations. It can involve both top and bottom mold sections (called a cope and drag). But for our beginner purposes, let’s look at a simple open-faced sand mold.

Materials

• Fine-grain silica sand
• Binder, such as sodium silicate, which helps the mold hold its shape
• Model or pattern if you’re using one
• Mold release spray
• Container called a flask in which to create the mold
• Ramming tool
• Acetylene torch

Steps

1. Prepare your model with mold release spray.
2. Mix your silica sand and binder. Depending on the type of sand and binder you use, a good ratio is between 5:1 and 10:1 sand to binder.
3. Embed the model in a thick layer of your mixture. Pack it in around all the edges. Use the ramming tool if necessary.
4. Remove the model.
5. Burn the surface of the model with your torch. This creates a barrier to prevent molten glass from seeping through.
6. Your mold is now ready to accept the liquified glass material!

Watch artisans demonstrate this fascinating process at an art museum workshop: 

Final Thoughts on Glass Moldmaking

As you can see, making your own glass molds takes patience and practice—whatever method you’re using. 

But with a bit of time and effort, making your molds can spark your creative spirit and elevate the excitement of kiln casting. To get great results, make sure you have a kiln that’s safe, precise, and easy to use, like the casting companion from Hot Shot.

Now, where will your imagination lead?