Going back to the ancient Egyptians, artisans have been making beautiful, functional objects via glass casting. Combining technical and artistic challenges, the versatile process of melting and molding glass can create jewelry, decorative objects, or lots of different practical items. It’s a fun, fulfilling hobby, but it’s more complex than other glass working techniques you may already know. So get to know the basics with this step-by-step guide to glass casting for beginners.

Glass Casting Definition

Glass casting involves melting glass in a furnace or kiln to make it molten and malleable, then allowing it to cool and harden in a mold.

Cast Glass Projects and Applications

As a hobbyist, exploring glass casting offers great opportunities for artistic growth. Bring your creative vision to 3D life by casting glass that’s transparent, translucent, or opaque, with a range of textures, colors, and visual effects

Images sources left to right, top to bottom: Morganica, marjorieanns, Mark Abildgaard, OLaLaVintage, Tiffany Price Coley

Here are a few glass casting project ideas to get you started:

• Sculptures
• Paperweights
• Bowls
• Vases
• Pendants and other jewelry components

What You Need to Cast Glass

Here’s a look at the most important materials and equipment you need for glass casting.

Image Source: Bullseye Glass Co.

Casting Molds

Learning how to make glass molds is the first key to success. It’s how your project takes shape. Molds can be made from plaster, ceramics, metal, or refractory fiberboard. You’ve also got a range of mold types to choose from, including:

Molds are available through a wide array of online retailers of glass working supplies.

• Open-faced, with a flat side or shallow cavity, often used for simple, shallow glass forms like plates, tiles, or shallow bowls.
• Closed, with two or more parts that fit together to create more complex and detailed glass objects, such as figurines or sculptures.
• Lost-wax, with a wax model of your desired shape encased in a mold shell. When the mold is heated, the wax melts away, leaving a cavity that can be filled with molten glass.
• Sand, in which a model is pressed into a mixture of sand and a bonding agent to create a mold cavity—commonly used for larger glass objects or artistic installations.
• Graphite molds, for casting glass at extremely high temperatures.
• Inclusion molds, allowing for additional materials or elements, such as metals or different colored glass, to produce unique designs.

Your choice depends on how complex your project vision is, as well as the type of glass you’re using and your casting technique (more on that in a bit).

Glass Casting Kiln

You’ll need a kiln large and powerful enough for your projects. That means something that can accommodate the size of your molds as well as the temperatures required by your chosen techniques.

For example, Hot Shot Ovens make a glass kiln we call the Casting Companion, which heats up to 2,000 while staying cool to the touch on the outside. So it’s perfect for small casting projects right on the bench in your home studio!

Casting Glass

There’s a specific type of glass, unsurprisingly called “casting glass,” that’s ideal for the process.

To facilitate melting, casting glass comes in smaller pieces such as frits, stingers, or even powder.

It has a lower melting temperature than other types of glass, which helps prevent damage to your molds and reduces the risk of thermal shock. It’s also usually formulated to have low viscosity when melted, which means it can flow easily into your molds and fill in the fine details.

In addition, it may have a higher coefficient of expansion, so it expands more when heated and contracts more when cooled—helping to ensure that the glass cools and solidifies uniformly without cracking.

Different glass manufacturers have different casting glass specs; talk to your preferred supplier about the exact type that’s best for your project.

Safety Gear & Considerations

• Respirator for mixing materials
• Insulated gloves and protective clothing
• Workspace with good ventilation

This is by no means an exhaustive list of materials and tools. Other helpful items include a scale, various cleanup materials, and more. Consult suppliers and experts on the needs for your particular project.

Basics of the Casting Process

Transforming molten glass into a solid three-dimensional object takes several key steps. These vary depending on your project, materials, and casting technique. Here’s a general overview of the process.

1. Design. What’s your inspiration? Clarify your vision, including factors such as shape, size, texture, and any desired inclusions. If you’re making your own mold, you can shape your design in wax and create a plaster mold over that. Or acquire a mold in your desired shape.
2. Mold preparation. You may need to coat the interior surface of the mold with a mold release agent to facilitate the removal of the cast glass later on. Position any desired inclusions or materials within the mold, such as metal wires, glass shards, or other decorative elements.
3. Firing. Preheat your kiln to the desired casting temperature, which can range from 1,300 °F to 2,000 °F depending on the technique and the glass used. Place your glass materials in a crucible or other heat-resistant container and place it in the furnace to melt the glass. Melt times vary by material and other project parameters. 
4. Filling the mold. Once the glass is completely molten, remove the material from the kiln (carefully and with all appropriate safety gear!). Pour into your prepared mold, filling the entire cavity. Watch for air bubbles or empty void spots. Let the material settle, gently tapping the mold to release any air bubbles if needed.
5. Cooling and annealing. Controlled, gradual cooling is essential to minimize internal stresses and prevent cracking or breakage. Glass annealing involves holding or soaking the glass at a midpoint temperature (Bullseye Glass currently recommends 900 °F), followed by slow, steady cooling to room temperature.
6. Removing and finishing. Carefully remove the glass from the mold. Clean the casting to remove any residual mold material, release agents, or other debris. Grind, polish, or add surface treatments as desired.

Inside the Different Glass Casting Techniques

Glass casting involves either melting glass into the mold while inside the kiln, or pouring the liquified material into your mold, where it hardens and takes shape.

Kiln Casting

Place your casting glass in your mold, then place the mold in the kiln. Fire the mold at your target temperature, depending on the type and thickness of your glass and your mold.

Pâte de Verre

Glass pasting (the term above is French) uses finely crushed glass as well as water and other materials to produce a textured or frosted look. Fire the mold at 1300 °F to 1400 °F.

Lost Wax Casting

Also known as investment casting, this technique involves building a mold around a wax shape. Melt away the wax and allow the mold to cure. Then fire the mold up to ~1525 °F, melting the glass and allowing it to flow into the cavity created by the wax.

Sand Casting

In this classic and still popular technique—well suited to larger-scale projects—you create or carve your mold using a mixture of sand and a binder material. Then pour the molten glass into the mold to cool and harden.

Tips, Tricks & Troubleshooting

From mold preparation to safety precautions, you’ve got plenty to consider when embarking on a glass casting adventure. Here’s a rundown of key pointers to keep in mind.

• Handle with care. You’re dealing with glass, after all. Never shortcut the cooling and annealing process. Practice your pouring technique. Use gloves and protective equipment.
• Minimize air bubbles. Vibrate or tap the molten glass in the mold to get trapped air out and avoid the frustration of finding these imperfections when it’s too late to fix them.
• Get the shape you want. Take the time to select or design / create the mold with all the details you envision. Don’t be afraid to try some of the different techniques described above.
• Control the temperature. Consistent, accurate firing is key to avoid incomplete melting or cracked glass. Use a reliable glass kiln with precise control.
• Keep learning. Glass casting is tricky business. What we’ve presented here is just the beginning! Give yourself every opportunity to develop your skills, whether through classes and workshops, books, or online tutorials and forums.

Closing Thoughts

As a glass caster, you can create one-of-a-kind pieces that reflect your artistic sensibilities. Each casting has its own personality, embodying the delicate balance of design, technique, and the unique and fascinating properties of glass.

Glass casting is far from the easiest glass working hobby. But the joy of holding a finished glass casting in your hands, knowing it’s an original creation, is hard to beat. Now go cast your heart out!