What is kiln formed glass? When exposed to heat, glass becomes soft and malleable. This allows glass artists to alter its shape or fuse multiple layers of glass together to create new textures or color combinations. At high enough temperatures, glass even liquefies, allowing artists to pour it into (or over) a mold or contour to create new forms.
Once the artist has achieved the desired effect, the glass is allowed to slowly cool and stabilize (or anneal). And the result is kiln formed glass!
9 Types of Kiln Formed Glass Techniques
One of the most exciting parts of being a glass artist is combining various kiln formed glass techniques to create unique, one-of-a-kind glass art. Once you understand these different glass firing techniques, the only limit is your creativity (as well as the capabilities of your glass kiln and glass kiln controller)!
Below is an overview of nine different kilnforming techniques – to give you inspiration for your next kiln formed glass art project!
1. Fused Glass
Fusing glass is a kilnforming technique that involves heating two or more layers of glass, and then allowing them to cool, so that they join together to form a single piece of kiln formed glass.
How fully the multiple layers of glass fuse together depends on your firing temperature. The hotter the kiln, the more uniform the fuse! Below are several different types of glass fuses:
- Full Fuse: The layers of glass are heated up until they liquefy and completely merge together, cooling to form a single, smooth piece of kiln formed glass. Full fusing can be used to create unique and beautiful color combinations.
- Contour Fuse: Contour fusing uses a lower firing temperature than a full fuse. In contour fusing, the different layers of glass are heated up enough to fully join together while remaining distinct separate layers. In contour fusing, both layers of glass get hot enough to lose some of their initial shape, becoming smooth at the edges.
- Tack Fuse: Tack fusing involves even lower temperatures than contour fusing. In tack fusing, different pieces of glass are heated up just enough to join together at the point of contact, with both layers retaining their original shape. Tack fusing can be used to create new textures or shapes.
As you can imagine, glass fusing is a versatile kilnforming technique that lets you craft new textures, colors, and even shapes! However, it’s important to make sure that the different layers of glass are compatible. Fusible glass has a higher quality grade than standard glass. Additionally, the different layers of glass need to have compatible viscosities (which isn’t always indicated by matching COEs!).
2. Glass Draping
Glass draping is another popular kiln formed glass technique. Glass draping uses heat and gravity to change the shape of a sheet of glass. For glass draping, you “drape” the glass sheet on top of a convex mold and heat up the glass until it at least partially liquefies. Gravity ensures the molten glass drapes around the convex mold. Higher temperatures lead to more dramatic results. Glass draping can be used for everything from creating conventional plates and bowls to producing abstract, other-worldly shapes!
3. Slumped Glass
Slumping is just like draping, only inversed! For slumping glass, a glass sheet is placed inside a concave mold. The glass is then heated up until it partially liquefies, taking on the shape of the mold. Since slumping glass occurs within the mold, it leads to more predictable results, and is used to create plates, bowls, cups, or decorative molds. The higher the temperature, the more fully the glass takes on the shape of the mold.
4. Glass Casting
Glass casting is similar to slumping. However, with glass casting enough glass is placed within the mold to fill it entirely – so that when the glass melts and then cools, it anneals into a solid object. Glass casting is a kiln formed glass technique that’s used to create ornaments, paper weights, and standalone glass art.
5. Glass Crackle
Glass crackle is a decorative kilnforming technique that most typically involves fusing together three layers of glass. The middle layer of glass is then shattered in a controlled method – or you can create the “crackled” middle layer using glass frit and fiber paper to create a crackled effect once it’s heated and allowed to melt. During glass crackling, the three layers of glass are fused together, and the outer layers are left intact so that the final piece retains a smooth (and safe!) outer layer.
There are also several alternative methods to create a crackle effect, some of which use distilled water and glass powder, which you can read about here!
6. Pot Melting
Pot melting is another decorative kilnforming technique that involves allowing glass to melt through a hole in the bottom of a pot – onto a primed kiln shelf or into a contained mold – to create swirls and ripples and other textured effects!
Watch our partners at Delphi Glass walk you through how to incorporate pot melting into your kiln formed glass projects.
7. Fire Polishing
Fire polishing is a “finishing” technique. Typically used after cold working glass, the glass is then heated up until it returns to its original shiny and smooth state.
8. Bubble Squeezing
A bubble squeeze is a “preparatory” technique before kilnforming glass. Bubble squeezing is used to create more even fuses by slowly heating up glass to allow trapped air to escape. Bubble squeezing reduces the number of bubbles, as well as their size, resulting in more uniform (and structurally sound!) kiln formed glass.
Finally, we get to annealing, which is the final step in kilnforming glass. Annealing glass is less of a technique, and more of a necessity! Annealing is a controlled cooling process. If you allow kiln formed glass to cool too quickly, it leads to all kinds of issues – like thermal shock, breakage, shattering, stress fractures, and structural weakness. An advanced glass kiln controller like TAP or TAP II by SDS Industries automatically (and precisely) cools glass at a controlled, highly specified ramp rate – keeping both glass and artists from being exposed to unnecessary stress!
Glass Supplies for Kilnforming Glass
Excited to get started? Before getting started on your next kiln formed glass project, you’ll need the right supplies! Below are brief explanations of the different glass supplies you’ll need for kilnforming!
Glass Kilns and Glass Kiln Controllers
Of course, to kiln form glass, you’ll need a kiln – and a kiln controller – that’s capable of glass firing. Glass kilns are specifically designed to heat glass to very precise temperatures so it can be fused, slumped, or cast.
(Some glassblowing artists also use a dedicated annealing kiln to slowly cool down blown glass that’s been heated outside of kiln to improve its durability and prevent the glass from experiencing thermal shock).
However, in addition to your kiln, it’s important to choose the type of kiln controller. TAP Kiln Controllers by SDS Industries provide glass artists with an advanced programmable digital controller that’s precise, simple, and easy-to-use. TAP Controllers are capable of executing complex schedules with multiple ramp rates to ensure your kiln formed glass comes out just the way you wanted! With TAP Controllers, you can store an unlimited number of firing schedules – so you always have all your glass firing schedules on-hand for when you need them. And with TAP Kiln Control Mobile, you have the convenient option to control and monitor your kiln formed glass firing right from your phone or tablet!
Types of Accessory Glass
Once you have the right kiln and the right kiln controller, you’ll also need glass. Glass used for kilnforming – also known as accessory glass – comes in several forms:
- Glass Frit: Glass frit is ground fusible glass that is used for filling spaces or creating crackled, mosaic, grainy textures, or for adding fine details to glass art.
- Sheet Glass: Available in a variety of sizes, sheet glass is used for kilnforming, fusing, and mosaics.
- Glass Rods, Noodles, Stringers, and Ribbons: Glass rods, noodles, and stringers are long, narrow strips of glass that are fused to other pieces of glass to create patterns, textures, or other artistic effect. Glass ribbons are a flatter, wider alternative that are perfect for fusing.
- Glass Confetti: Glass confetti consists of small, irregular, ultra-thin flakes of glass and are used for adding touches of color to your kiln formed glass.
- Glass Billets: Billets are precisely cut sheets of fusible glass that are the perfect size for casting.
Accessory glass comes in all sorts of colors and levels of translucence – so that you can create the perfect effects for your kiln formed glass projects. Just make sure that when you’re shopping for accessory glass, that the glasses you choose are compatible. A good place to start is by making sure that the glasses have matching COEs – or coefficients of expansion – which means they’ll expand or contract at the same rates when heated up or cooled down. However, there are other factors that affect compatibility, so it’s always recommended that you do plenty of research before purchasing glass and start by doing a test fuse for glasses you’re not familiar with!
Explore Glass Kiln Controllers by SDS Industries
The TAP and TAP II Controllers by SDS Industries provide artists with the most advanced, precise, and easy-to-use glass kilns controllers on the market today. With responsive touchscreen controls, an intuitive graphical UI, and integration with the TAP Kiln Control Mobile app, TAP Kiln Controllers can pair with any relay-controlled kiln or oven.
We invite you to explore our selection of programmable kiln controllers, standalones, and conversion kits on our online store. You can also purchase TAP Digital Controllers or TAP Controlled Kilns and Heat Treat Ovens through one of the following distributors:
- Hot Shot Oven & Kiln
- Mobile Glassblowing Studios, LLC
- Jen-Ken Kilns
- Kiln Frog
- Sheffield Pottery
- Delphi Glass