When it comes to kiln forming glass, learning glass fusing techniques will unlock new possibilities for your kiln formed glass projects!
These techniques have a wide range of applications and are absolutely essential if you plan on using more than one layer of glass.
Excited to get started? Let’s go!
What is Glass Fusing?
Glass fusing is a group of kiln formed glass techniques that involves heating two or more layers of glass and then allowing them to cool. In the end, these two layers become one, joining together to form a single piece of kiln formed glass.
Your kiln’s firing temperature determines how these layers of glass combine. The hotter the firing temperature, and the longer the hold, the more complete the fuse.
Overview of Glass Fusing Techniques
Below are the three primary types of glass fusing techniques – from the hottest firing temperature to coolest (as well as from most to least uniform!):
- Full Fuse [1450°F to 1490°F (788°C to 810°C) for 90 COE Glass]: A full fuse is involves heating up two or more layers of glass to a high enough temperature that they totally liquefy, merging together to cool into a single, uniform layer.
- Contour Fuse [1400°F to 1450°F (760°C to 788°C) for 90 COE Glass]: Also known as a “soft tack,” contour fusing involves heating up both layers of glass enough that they lose some their initial shape. In contour fusing, both layers become smooth at the corners, while remaining distinct, separate layers.
- Tack Fuse [1350° F to 1400° F (732°C to 760°C) for 90 COE Glass]: A “hard tack” fuse involves heating up two layers of glass so that they only fuse together at the point of contact – while completely retaining their initial shape.
Throughout this article, we’ll be explaining these different glass fusing techniques, providing tips, exploring their applications, and sharing examples!
Applications for Glass Fusing Techniques
Glass fusing techniques are used to achieve a variety of effects. You can play around with different fuses to:
- Create new color combinations, swirls, and patterns.
- Create new textures – both smooth or more pronounced.
- Add depth and dimensions to glass pieces.
- Create new shapes.
- Create scenes and compositions.
You can incorporate fusing glass techniques into a variety of different kiln formed glass projects – both decorative and functional.
These include (but aren’t limited to!):
- Plates
- Glasses
- Bowls
- Coasters
- Jewelry
- Artistic Scenes
- Ornaments
- Sun Catchers
- Picture Frames
- Glass Sculpture
As you can see, glass fusing techniques are an essential part of any glass artist’s arsenal – so let’s help you learn more about these techniques!
Things You Need to Know Before Fusing Glass
Before fusing glass, preparation is key. Below are a couple of things you need to know before firing up your glass kiln:
- Make sure that all of your glass layers are compatible: Fusible glass comes in different COEs. COE stands for “coefficient of expansion.” This number indicates how much glass expands when heated. For glass art, 90 COE and 96 COE are the most common types of fusible glass. But it’s important to pick a single COE for every layer of your project – and stick to it! Attempting to fuse incompatible glass leads to cracks, failed fuses, and having to try to clean up broken glass from your kiln (not fun!).
- Consider creating a sketch of your finished piece before you begin cutting glass: If you’re more experienced, this might not be necessary – but it can be super helpful to sketch out your finished piece on a sheet of paper before you begin cutting glass.
- Decide what type(s) of fuse(s) you want to execute: Based on what characteristics you want your finished piece to have, decide which type(s) of fuse(s) will help you achieve those effects.
- Methodically cut and clean your glass (if applicable): You will want to carefully cut each layer of glass into the appropriate shape before fusing. We recommend investing in a good pair of glass cutters, tracing the outline you want to cut directly on the glass, and then working slowly to avoid any errors. You can also use a tabletop glass grinder to further refine your glass pieces. Afterwards, carefully clean your glass to remove any debris prior to kiln firing.
- Properly prime your kiln shelves – or use fiber paper (or both!): Before firing glass, it’s important to prep your kiln to ensure that your glass doesn’t melt to the inside of your kiln. We recommend priming your kiln shelves with kiln wash (also known as shelf primer) or using fiber paper underneath your project – or, ideally, both! Even if you have a kiln that uses fiber brick, we recommend priming the bottom of your kiln just in case.
- Be careful when loading your project into the kiln – or assemble your glass pieces inside the kiln: Carefully arrange your project on an appropriate kiln shelf and then slowly slide your shelf into the kiln at least 1” from the kiln floor. Make sure to maintain a 2” of clearance from heating elements and the walls of the kilns. Alternatively, depending on your kiln’s configuration, you can assemble your layers directly inside of your kiln.
- Find a firing schedule for your type of glass and the technique you’re trying to achieve: Choosing the right firing schedule (and making sure you enter it into your controller correctly) is essential to achieving the results you want. Take some time to do some research online to see what type of schedules other artists are using – and you may need to do some experimenting if you’re a newer artist. The good news is that the most advanced glass kiln controllers like TAP Kiln Controllers by SDS Industries let you name, save, and easily access an unlimited number of firing schedules. Once you perfect your schedules, you’ll never have to recreate them again!
- Make sure you have a glass kiln controller that’s capable of executing firing schedules of glass: A manual kiln with a kiln sitter or a single setpoint controller won’t be up to the task of precisely executing the specific ramp rates or complex, multi-step firing schedules needed to fuse glass. You will need a programmable digital process controller.
Like any craft, mastering glass fusing techniques takes time, preparation, and practice. There’s a little bit of a learning curve! We encourage you to be patient with yourself, take your time, not be afraid of experimentation, and to learn from your failures as well as your successes.
The Importance of Annealing
Before executing a glass fusing technique, it’s important to remember: You absolutely have to anneal your glass!
Annealing glass requires a controlled cooling process. To anneal glass, hold it at a steady temperature to allow the glass to stabilize and strengthen. COE 90 glass is typically annealed at 900°F (482°C).
For glass fusing techniques, annealing is essential for getting the fuse to hold and for two separate pieces of glass to become one! If annealing isn’t done properly, fused glass is susceptible to breaking where the layers meet due to stress. This can happen suddenly or further down the road.
To protect your piece from breakage, make sure your fusing glass firing schedule includes an annealing hold in the cooling stage.
Examples of Glass Fusing Techniques
A picture is worth a thousand words. We’ll be sharing some visual examples of different fused glass techniques. Hopefully this will help you visualize which technique(s) is right for your next project!
Full Fuse Example
In this project, manufactured swirly glass was fully fused on top of a layer of white glass to achieve this effect. Notice how the two layers are completely merged to achieve a single, smooth piece of kiln formed glass.
A full fuse can be used to create new color combinations, swirls, and patterns.
Contour Fuse Example
For a contour fuse, the different layers of glass are smooth and rounded while retaining some of their initial shape. This creates a sense of dimension, depth, and can be used to create smooth textures.
This glass fusing technique can be used to create compositions like the butterfly and leaf in this example.
Since the layers of glass don’t get as hot, the separate layers remain distinct while being smooth to the touch.
Tack Fuse Example
For a tack fuse, each layer retains its initial shape.
In this composition of a desert landscape, notice how the different layers are tacked together and retain their edges.
Tack fusing can be used to create rough textures, compositions with a greater degree of depth, or two connect two different pieces of glass to create new shapes.
Power Your Kiln with The Most Advanced Glass Kiln Controllers
Whether you’re using glass fusing techniques, slumping, or casting, choosing the right kiln controller can help you execute your kiln formed glass firings with more ease, precision, and consistency.
The TAP II and TAP II Pro Controllers by SDS Industries provide users with intuitive touchscreen controls, PID-driven precision, and the ability to name, save, and access and unlimited number of firing schedules with an unlimited number of steps. They even include tools to help streamline managing your glass art studio!
With integration to the TAP Kiln Control Mobile app, you will be able to monitor your projects in real-time, receive real-time alerts, and enjoy remote kiln control through your smartphone or tablet! 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:
- Evenheat
- Hot Shot Oven & Kiln
- Paragon Kilns
- Mobile Glassblowing Studios, LLC
- Jen-Ken Kilns
- Kiln Frog
- Sheffield Pottery
- Delphi Glass
Fused Glass Techniques FAQ
What type of kiln controller will I need for fusing glass?
Fusing glass requires an automatic process controller that’s capable of executing complex, multi-step firing schedules with precise ramp rates and hold times.
With a manual kiln or kiln sitter, you simply won’t have the precision you need to successfully fuse glass.
Furthermore, we recommend using a PID temperature controller. That way, your kiln adheres as close to the programmed schedule as possible, resulting in more consistent and precise glass fuses.
You can learn more about different types of kiln controllers to find the right ones for your glass fusing projects at 14 Types of Electric Kiln Temperature Controllers.
Can I fuse 90 COE glass with 96 COE?
No, you should not attempt to fuse layers of glass that have a different coefficient of expansion. Doing so is likely to result in failed fuses or breakage since the different layers of glass will expand (and contract) at different rates.
When planning a fused glass project, make sure to make sure all of your glass layers are 1.) fusible and 2.) have compatible COEs.
What are good brands for fusible glass?
As a former full-time glass artist, my go-to brand is Bullseye Glass. Bullseye sells a wide array of high quality 90 COE accessory glass in sheets, rods, stringers, ribbons, billets, and more.
Additionally, Bullseye glass sells molds and casts, and provides tons of great glass firing resources, making them a great one-stop-shop for glass supplies.
Delphi Glass is another great place to shop for glass supplies, where you buy supplies from Bullseye Glass, as well as other reputable art glass suppliers.
How do I make sure the glass fuse is successful?
To ensure a successful glass fuse, here are a few steps you can take:
- Only use compatible glass with the same COE.
- Research firing schedules to find one that works with your type of glass.
- Clean all debris from the glass prior to attempting a fuse.
- Make sure that your glass firing schedule includes an anneal during the cooldown phase.
Additionally, it can be super helpful to use a controller that includes error reports and advanced diagnostics – as well as to document all of your projects in a kiln notebook. That way, you can pinpoint errors if things go wrong and become a more consistent artist over time!
Can you fuse glass in your oven?
No! Fusing glass requires using a specialized kiln or oven that utilizes an automatic kiln controller.
Attempting to fuse glass in a standard kitchen oven is a terrible idea for the following reasons:
- A standard kitchen oven won’t be able to reach high enough temperatures for glass to fuse.
- Kitchen ovens won’t be able to execute the precise ramp rates or hold times that are necessary for firing glass.
- When heated to high temperatures, glass liquefies and can drip onto the floor or walls in your oven – which would be an absolute nightmare to clean up.
We understand you’re excited to get started! But please make sure you have the right type of kiln to safely and successfully execute these glass fusing techniques!
Can any type of glass be fused?
Technically, any type of glass can be melted and then fused back together. However, attempting to fuse a random piece of glass to a different piece of glass has an astronomically small probability of a successful fuse.
That’s because every piece of glass has a different melting point and coefficient of expansion.
Purchasing glass that’s marketed as “fusible” means that it will melt at a specified setpoint and expand at a specified coefficient, allowing for successful glass fuses with other compatible glasses.
Trying to mix and match glasses will result in cracks, failed fuses, and a lot of wasted time.
Some artists take things a step further and only use compatible glass from a specific brand – since different brands might have slightly different specs.
