That sinking feeling when you find a crack in a “finished” piece? It’s a frustrating, all-too-common experience. But the problem isn’t your skill—it’s a tiny number you might have overlooked: the COE. This number, the Coefficient of Expansion, is the golden rule of glass fusing. Understanding the critical difference in the coe 90 vs 96 debate is the most important thing you can learn. It’s the key to making sure your choices with 90 vs 96 coe glass lead to strong, stable art that comes out of the kiln exactly as you envisioned.

Key Takeaways

• Never Mix Your COEs: This is the golden rule of glass fusing. Combining glass with different COE ratings creates immense internal stress as the pieces expand and contract at different rates, which will cause your project to crack.
• Choose the Right Glass for Your Goal: Use COE 90 for its vast color palette and stability, making it perfect for detailed, intricate work. Opt for the often more affordable COE 96 when your design calls for brilliant, bold colors or you’re working on a larger scale.
• Keep Your Systems Separate: To prevent costly mistakes, physically separate your COE 90 and COE 96 glass in your studio. Just as importantly, always use the specific firing schedule recommended by the manufacturer for the type of glass you are firing.

What is COE in Glass Fusing?

If you’ve spent any time in the world of glass fusing, you’ve definitely heard the term “COE.” It’s one of those fundamental concepts that can make or break your projects—literally. Understanding what COE is and why it matters is the first step toward creating beautiful, stable fused glass art that lasts. Think of it as the golden rule of your studio: know your COE, and you’ll save yourself a lot of heartache. It’s the secret language that helps different pieces of glass play nicely together in the heat of the kiln.

What is the Coefficient of Expansion?

Let’s get straight to it. COE stands for Coefficient of Expansion, which is a fancy way of saying it’s a measurement of how much glass expands when it gets hot and shrinks when it cools down. Every piece of fusible glass has a COE rating. For example, a glass labeled as COE 90 expands 0.0000090 inches for every degree Celsius its temperature is raised. The two main types you’ll work with are COE 90 and COE 96. That tiny difference is a huge deal when you’re firing glass to over 1,000 degrees.

The Science Behind the Number: Measuring Expansion

So, what do those numbers—90 and 96—actually mean? It’s simpler than it sounds. The COE number tells you exactly how much a specific type of glass will expand when heated and shrink as it cools. For example, a piece of COE 90 glass expands at a rate of 90 millionths of an inch for every one-degree Celsius increase in temperature. Meanwhile, COE 96 glass expands just a little bit more, at 96 millionths of an inch. It seems like an incredibly tiny difference, and on its own, it is. But when you’re fusing glass in a kiln that reaches extreme temperatures, that minuscule variation becomes the most important factor in your project’s success.

Here’s why that tiny difference is a huge deal. When you fuse two pieces of glass with different COE ratings, they expand and contract at different speeds inside the kiln. As the piece cools, the glass with the higher COE will shrink more than the glass with the lower COE. This creates an incredible amount of internal stress at the seam where the two types of glass meet. The result? Your beautiful, newly fused piece will almost certainly crack or, in some cases, even shatter as it cools. This isn’t a matter of ‘if’ but ‘when.’ Mixing COEs is the number one cause of failed fusing projects, and it’s completely avoidable.

Beyond preventing cracks, your choice between COE 90 and COE 96 also influences the final look and feel of your art. Because COE 90 glass expands and contracts a bit less, it’s known for its stability and is often favored for intricate, detailed designs that require precision. On the other hand, COE 96 glass, with its slightly higher expansion rate, is celebrated for producing exceptionally brilliant and vibrant colors. Many artists choose it for bold, colorful pieces. Understanding these characteristics helps you not only avoid disaster but also make intentional artistic choices that bring your vision to life.

Why COE Can Make or Break Your Glass Art

Here’s why this number is so important: for a fused piece to be successful, all the glass you use in it must have the same COE. When you mix glasses with different COE ratings, they expand and contract at different rates inside the kiln. This creates immense internal stress in the finished piece. As the glass cools, this tension results in cracking or even shattering. This can happen right away as the piece cools, or it can be a ticking time bomb that breaks days or even weeks later. Sticking to one COE per project ensures all your glass components are compatible.

Does COE Matter for Traditional Stained Glass?

Now that we’ve covered the absolute necessity of matching COEs for fusing, you might be wondering if the same rule applies to traditional stained glass. The short answer is: not really. In a traditional stained glass project, each piece of glass is an individual component, separated by lead came or copper foil. This metal framework is flexible and can easily accommodate the tiny amounts of expansion and contraction that happen as the glass heats and cools with ambient temperature changes. Because the pieces aren’t melted together into one solid mass, the internal stress that plagues incompatible fused glass simply doesn’t build up. This gives you the creative freedom to mix and match different types of stained glass without worrying about their COE.

Testing for Glass Compatibility: A Quick Guide

So what happens when you have scrap glass and you’re not sure of its COE? While you can’t determine the exact COE without lab equipment, you can test for compatibility. A common method involves using two polarized lenses to check for stress after fusing a sample to a piece of known COE glass. However, the easiest approach is prevention. Keep your COE 90 and COE 96 glass strictly separated in your studio. Label your storage bins clearly. This simple organizational habit will prevent costly mix-ups and ensure your projects come out of the kiln strong and beautiful.

COE 90 vs. 96: What’s the Difference?

At first glance, a sheet of COE 90 glass and a sheet of COE 96 glass might look pretty similar. They’re both beautiful, full of potential, and ready for your next project. But in the world of glass fusing, that small number makes a world of difference. Think of it as a fundamental personality trait of the glass. It dictates how it behaves in the kiln, what other glass it can be fused with, and even the colors you can achieve. This is one of the first major decisions you’ll make as a glass artist, and it shapes your entire collection of materials.

Choosing between COE 90 and COE 96 glass isn’t about which one is “better”—it’s about which one is right for your specific project and artistic style. Many artists end up working with both, but they learn early on to keep their supplies completely separate, often with dedicated shelves and scrap bins for each. Understanding the key distinctions will save you from the frustration of cracked projects and wasted materials, letting you focus on the creative side of things. Let’s break down the main differences so you can confidently choose the right glass for your studio.

Understanding How They Melt and Flow

The most critical difference between COE 90 and COE 96 is how much they expand when heated and shrink when cooled. This is what the COE number actually measures. Because they move at different rates, you absolutely cannot fuse them together. Even that small difference creates immense stress within the piece as it cools down in the kiln. This tension will almost certainly cause the glass to crack, either during the cooling process or, sometimes, weeks or even a year later. To avoid this heartbreak, always keep your COE 90 and COE 96 scraps and sheets clearly labeled and stored separately.

Comparing Texture, Hardness, and Workability

Beyond the chemistry, these two types of glass feel and behave differently in your hands and in the kiln. COE 96 glass is known for being smoother and softer, which many artists find makes it easier to cut cleanly. If you’re new to glass cutting or working on a project with lots of simple curves, you might prefer the feel of COE 96. On the other hand, COE 90 glass often has a slightly rolled texture from its manufacturing process. This isn’t a flaw; it’s just a characteristic. However, this texture can sometimes trap tiny air bubbles between layers, which can be a beautiful design element or a minor frustration, depending on your desired outcome.

This difference in feel extends to their hardness. COE 90 is a harder, denser glass that requires higher temperatures in the kiln to reach a full fuse. Its stiffness and stability at high heat make it the top choice for intricate, detailed work where you want your components to hold their shape without a lot of movement. In contrast, COE 96 glass is softer and melts at lower temperatures. This makes it more fluid and “forgiving,” allowing colors to blend beautifully and fill molds easily. For beginners, the lower firing range and softer nature of COE 96 can make the fusing process a bit more straightforward.

Comparing Color Palettes and Options

This is where your artistic preference really comes into play. COE 90 glass, largely produced by Bullseye Glass, is famous for its incredibly wide and vibrant color palette. If you’re looking for those stunning cranberry pinks, hot magentas, or unique, sparkly iridescent coatings, COE 90 is your go-to. On the other hand, COE 96 offers a fantastic and broad range of colors as well, but it doesn’t include some of those “hot” colors. It’s a workhorse glass with a reliable and beautiful spectrum, perfect for many different styles and designs. Your choice might simply come down to which color family speaks to you the most.

Which is More Budget-Friendly? Price and Availability

Budget is always a factor, especially when you’re starting out or working on a large-scale piece. Generally, COE 96 glass tends to be a bit less expensive than COE 90. This often makes it a popular choice for beginners who are building their initial supply collection or for artists creating larger architectural pieces where the cost of glass can add up quickly. Both types are widely available, so you won’t have trouble finding what you need, but if you’re looking to make your dollars stretch a little further, COE 96 is a great place to start your glass fusing journey.

How They’re Sold: By the Pound vs. By the Square Foot

When you’re stocking up on glass, you’ll notice a key difference in how COE 90 and COE 96 are priced and sold, which can definitely impact your budget. COE 90 glass is typically sold by the pound. This means the cost can vary depending on the thickness and type of glass you’re buying. When you do the math to convert it, the price often lands somewhere between $10 and $15 per square foot, making it a slightly more premium option. In contrast, COE 96 glass is usually sold by the square foot, with prices generally ranging from $8 to $12. This straightforward pricing makes it a popular and often more budget-friendly choice, especially if you’re working on larger pieces or just building up your studio’s inventory. Understanding this distinction helps you plan your projects and purchase materials wisely.

Key Differences in Firing Temperatures

Because they expand and contract differently, COE 90 and COE 96 glass also need to be fired at different temperatures and according to different schedules in your kiln. You can’t use the same firing schedule for both and expect perfect results. Each manufacturer provides specific firing guides for their glass, and it’s essential to follow them for the best outcome. Always check the recommended temperatures for slumping, tack fusing, and full fusing. Keeping a detailed logbook for your kiln firings is a great habit to get into, especially when working with different types of glass.

What the Manufacturers Say

The term COE stands for Coefficient of Expansion, which is the technical term for measuring how much the glass moves when its temperature changes. Manufacturers like Bullseye (COE 90) and Wissmach (COE 96) have perfected their formulas to ensure all the glass within their COE family is compatible with each other. This is why you can confidently fuse a Bullseye red with a Bullseye blue, but not with a Wissmach red. The manufacturers provide these numbers so you can build a reliable system in your studio and create strong, stable, and beautiful fused glass art without any unwelcome surprises.

COE 90: The World of Bullseye Glass

When artists talk about COE 90, they’re almost always talking about Bullseye Glass. This company has built its reputation on producing a stunningly diverse and rich color palette that is a dream for detailed work. If your project calls for specific, vibrant shades like cranberry pinks, hot magentas, or unique textures like sparkly iridescent coatings, COE 90 is where you’ll find them. This glass is often the top choice for artists creating intricate glass sculptures, custom jewelry, and other fine art pieces where color precision and visual depth are essential. The consistency and quality of Bullseye make it a reliable and inspiring medium for anyone looking to push their creative boundaries with kiln-forming. Exploring the world of COE 90 glass opens up a massive spectrum of color and possibility for your studio.

COE 96: Oceanside, Wissmach, and Brand Compatibility

Think of COE 96 as the versatile workhorse of the fusing world. While it also offers a beautiful and broad range of colors, it’s known for its reliability and inter-brand compatibility. Unlike COE 90, which is dominated by one manufacturer, you can find COE 96 glass from several companies, including Wissmach and Oceanside. The best part? As long as the glass is rated COE 96, you can mix and match brands within the same project without worrying about compatibility issues. This gives you more flexibility in sourcing your materials and can sometimes be a more budget-friendly option. This makes COE 96 glass a fantastic choice for everything from large architectural panels to everyday functional art like plates and bowls, where consistency and strength are key.

How to Choose the Right Glass for Your Project

Picking the right glass is one of the most important decisions you’ll make for any project. It affects everything from the colors you can use to the structural integrity of your final piece. Think of COE as the “language” your glass speaks—if you want different pieces to fuse together happily, they need to speak the same language. Let’s break down when to reach for COE 90 versus COE 96, so you can feel confident in your choice every time you start a new creation.

Perfect Projects for COE 90 Glass

Think of COE 90 glass as your go-to for projects that need to be strong, stable, and full of intricate detail. Because it expands and contracts less when heated, it’s incredibly reliable during the firing process. This makes it perfect for kiln-forming, detailed glass sculptures, and delicate jewelry where precision is key. If your design involves fine lines, sharp angles, or complex patterns, COE 90’s stability will help you achieve crisp, clean results. Its rich color palette also lends itself beautifully to sophisticated, gallery-quality work.

Perfect Projects for COE 96 Glass

When your project is all about brilliant, eye-catching color, COE 96 glass is your best friend. Its higher coefficient of expansion allows for some of the most vibrant and luminous colors available. This makes it an excellent choice for stained glass panels, colorful mosaics, and bold fused pieces where you want the colors to truly pop. COE 96 is also known for being a bit more forgiving and is often more affordable, which makes it a fantastic starting point for artists who are new to glass fusing or working on a budget.

A Guide to Working with Specialty Glass

Here’s the golden rule of glass fusing: you cannot mix glass with different COEs. Fusing a piece of COE 90 with a piece of COE 96 might seem fine at first, but their different rates of expansion and contraction will create immense internal stress. This tension, known as incompatibility, will almost certainly cause your piece to crack as it cools—or even weeks, months, or a year later. This rule applies to all fusible materials, including frits, stringers, and dichroic glass. Always double-check that every single element going into your kiln has the same COE.

How Cost Affects Your Choice

Your budget can definitely play a role in which glass you choose. Generally, COE 96 glass is less expensive, making it a practical option for beginners, students, or artists creating large-scale installations. You can experiment more freely without worrying as much about the cost of materials. On the other hand, COE 90 glass tends to be more of an investment and is often sold by the pound. While it costs more upfront, its reliability and suitability for complex, high-end pieces can make it a worthwhile choice for professional artists or anyone working on a special commission.

Setting Up for Success with COE 90 & 96

Once you’ve chosen the right glass for your project, the real fun begins. But a beautiful finished piece depends on more than just great design—it requires a solid process. Working with COE 90 and COE 96 glass isn’t complicated, but it does demand attention to detail. From setting up your kiln to storing your sheets, these practical steps will help you handle your glass with confidence and get the results you’re looking for.

Setting Up Your Kiln

Think of your kiln as your creative partner—it needs to be prepped and ready to go. Before you even think about firing, make sure your kiln shelf is clean and coated with a fresh layer of kiln wash or lined with shelf paper. This prevents the glass from sticking. Remember, COE 90 and COE 96 glass require different firing times and temperatures. Always check the glass manufacturer’s website for their specific firing guides, as these are your most reliable source of information. A proper setup is the foundation of a successful firing, so taking a few extra minutes here will save you a lot of headaches later.

Firing Different COEs in the Same Kiln Load

This is a question that comes up all the time: can you fire your COE 90 and COE 96 projects in the same kiln load to save time and energy? The answer is yes, but with one critical rule: the projects must be completely separate. You can never fuse glass with different COEs together in the same piece, as their incompatible expansion rates will cause it to crack. However, if you have two distinct projects—one made entirely of COE 90 glass and another of COE 96 glass—you can fire them simultaneously. The trick is to use a slow, conservative firing schedule that is gentle enough for both, especially when the pieces are similar in size. Just make sure they are separate items on your kiln shelf, never touching.

Controlling Kiln Temperatures Like a Pro

You can’t fuse glass with different COEs, like COE 90 and COE 96, together. Even a tiny difference in how they expand and shrink creates immense stress, which can cause the glass to crack as it cools—or even months later. This is why your firing schedule is so important. Following the manufacturer’s recommended schedule ensures the glass heats and cools at the right pace. The slow cooling phase, or annealing, is especially critical for relieving internal stress. Precise temperature control in your kiln is what gives your piece strength and stability, turning a fragile design into a durable work of art.

Your Must-Have Tools for Glass Fusing

Having the right tools makes your process smoother and more enjoyable. Beyond your basic glass cutter and pliers, consider adding a pair of polarized lenses to your kit. By holding one lens over your glass and looking through the other, you can spot the tell-tale signs of stress that are invisible to the naked eye. This is a simple way to check for compatibility issues before you fire. And of course, don’t forget the equipment that brings your vision to life, like high-quality molds for slumping and draping. Equipping your studio with the right gear helps you work smarter and create with more precision.

Your Studio Safety Checklist

Your safety is the most important part of any project. Always wear safety glasses when cutting or handling glass, and make sure your studio has good ventilation, especially when a kiln is running. Before starting a large project, it’s a great idea to do a few small test pieces to ensure everything is working as expected. And it bears repeating: always read the instructions from the glass manufacturer. They provide essential guidelines that are specific to their products. Following these simple safety practices protects you and helps ensure your projects turn out just the way you planned.

The Right Way to Store Your Glass

Good organization is key to a happy studio, especially when you work with different types of glass. If you use both COE 90 and COE 96 glass, you absolutely must keep them separate. Store them in clearly labeled bins, on different shelves, or even in separate areas of your studio to avoid accidental mixing. A small, unmarked scrap of the wrong COE can ruin an entire piece you’ve spent hours creating. This simple habit is one of the most effective ways to prevent frustrating and costly mistakes, letting you focus on your creativity without worrying about compatibility.

A Simple Tip for Keeping Your Glass Organized

Here’s a simple but non-negotiable habit for your studio: dedicate separate, clearly marked storage for your different glass types. This isn’t just about being tidy; it’s about protecting your art. A single, unidentified scrap of COE 96 glass mixed in with your COE 90 supply can cause a beautiful piece to crack. Use different shelves, labeled bins, or even separate rolling carts to keep them apart. Some artists use a color-coding system—like red tape for COE 96 and blue for COE 90—on their storage containers and even on the glass sheets themselves. This small organizational step is the best insurance against the heartbreak of incompatibility, ensuring your projects are strong and stable.

How to Avoid Common Fusing Problems

Working with fusible glass is incredibly rewarding, but a few common issues can trip up even experienced artists. The good news is that most problems are completely avoidable with a little bit of know-how. Understanding the science behind why glass behaves the way it does is your best defense against cracked projects and unexpected results. Think of it as learning the rules of the road before you start your car—it just makes for a smoother, safer, and much more enjoyable ride. By paying attention to a few key details like compatibility and temperature, you can save yourself a lot of frustration and ensure your beautiful ideas come out of the kiln exactly as you envisioned.

Why You Can’t Mix COEs

This is the golden rule of glass fusing: never mix glass with different COEs in the same project. It might seem tempting to use that perfect scrap of glass you have lying around, but if it’s a different COE, it’s a recipe for disaster. Here’s why: glass with different COE ratings expands and contracts at different rates when heated and cooled. Even a tiny difference between COE 90 and COE 96 glass creates immense internal stress. This stress will cause your piece to crack, either during the cooling process in the kiln or, heartbreakingly, weeks, months, or even a year later. Always stick to one COE for every single element in a single piece to ensure its strength and longevity.

Beyond COE: Other Factors in Compatibility

While matching your COE is the non-negotiable foundation of any successful fusing project, it’s not the only detail that matters. Think of it this way: even if two pieces of glass speak the same language (the same COE), they might have slightly different dialects. Each manufacturer provides specific firing guides for their glass, and it’s essential to follow them for the best outcome. A full fuse for a Bullseye COE 90 sheet might require a slightly different temperature or hold time than a tack fuse for a Wissmach COE 96 piece. Paying close attention to these recommended schedules for your kiln ensures that you get the exact result you want, whether it’s a smooth, fully fused piece or a textured, tack-fused design. This simple habit of checking the manufacturer’s guidelines will prevent unexpected outcomes and help you master your craft.

Troubleshooting Common Temperature Issues

Just as you can’t mix the glass itself, you also can’t use the same firing schedule for both types. COE 90 and COE 96 glass have different working properties and require specific temperatures and timing to fuse properly. Using a COE 96 schedule for a COE 90 project can lead to an under-fired, weak piece, while the reverse could cause your glass to overheat and lose its shape or detail. The best practice is to always refer to the manufacturer’s specific firing guides for the glass you’re using. Your kiln’s performance can also vary, so keeping a journal of your schedules and results is a fantastic way to dial in the perfect settings for your specific setup.

Simple Compatibility Tests You Can Do Today

What do you do with that mystery piece of glass in your scrap bin? While you can’t determine an exact COE without laboratory equipment, you can perform simple compatibility tests to see if it plays nicely with your other glass. One common method involves using two polarized lenses to check for stress between a sample of your known glass and the mystery piece after they’ve been fused together. Another great tool is a “Fuse It Test card,” which helps you visually check for stress lines. These tests are perfect for confirming that your glass is all from the same COE family before you commit it to a larger project, giving you peace of mind and saving your valuable materials.

Your Quality Control Checklist

Creating a simple quality control checklist for yourself is the best way to prevent COE-related mishaps. Before you even start cutting glass, get in the habit of running through these steps. First, confirm the COE of every piece of glass you plan to use. Second, keep your COE 90 and COE 96 glass stored in separate, clearly labeled containers to avoid accidental mix-ups. Finally, do one last check before you load the kiln. This simple, three-step process takes only a few moments but can be the difference between a stunning finished piece and a cracked one. Making this a routine part of your workflow will help you create beautiful, stable glass art every time.

Ready for the Next Level? Advanced Techniques

Once you’re comfortable with the basics of glass fusing and understand the key differences between COE 90 and 96, you can start exploring more creative and complex projects. Moving into advanced techniques means working with new materials, planning more intricate designs, and getting even more precise with your kiln schedules. It’s all about building on the foundation you’ve already set. Let’s look at a few ways you can push your glass art skills further.

How to Fuse with Dichroic and Other Specialty Glass

Working with specialty glass is one of the most exciting ways to add unique flair to your work. Dichroic glass, with its mesmerizing, color-shifting metallic coating, can transform a simple piece into something spectacular. Because COE 90 glass is often handmade, you’ll find a wide variety of specialty options, including dichroic, designed specifically for this system. When you introduce any new glass, always double-check that its COE matches your project’s base glass. Experiment with layering dichroic glass on top of or between other pieces of glass to see how the colors and reflections interact after firing.

Expert Tips for Tackling Complex Projects

As your projects become more ambitious, planning becomes essential. The most important rule remains the same: never mix different COEs. If you combine glasses with different expansion rates, they will shrink and cool differently, which can cause your beautiful work to crack or shatter. For intricate designs, sketch your ideas first. Consider the thickness of each piece of glass and how it will flow when melted. Using molds can help you achieve specific shapes and add three-dimensional qualities to your art. For large or layered pieces, it’s always a good idea to run a small test fire with scraps to predict how your glass will behave.

How to Master Complex Firing Schedules

While basic firing schedules work for simple projects, advanced designs often require a more customized approach. Both COE 90 and COE 96 glass need different firing temperatures and times, so it’s crucial to check the manufacturer’s specific firing guides. A project with multiple layers or significant thickness needs a slower heating and cooling cycle to prevent thermal shock. You might need to add longer holds at certain temperatures to ensure the glass fully fuses and properly anneals. Keeping a detailed log for your kiln is a great habit. Document your schedules, the glass you used, and the results to refine your process over time.

How to Choose Materials for Advanced Designs

Your choice of glass has a huge impact on the final look of your piece. Think about the aesthetic you want to achieve. If you’re aiming for bold, brilliant colors, COE 96 glass is often an excellent choice due to its vibrant palette. If your design calls for richer, deeper colors or interesting textures, COE 90 offers a wider range of options, especially for kiln-forming techniques. Don’t forget about accessory glass like frits, powders, and stringers. These materials are fantastic for adding fine details, creating gradients, or introducing delicate patterns that can take your advanced designs from great to truly exceptional.

Your Go-To Resources and Firing Schedules

Once you’ve chosen your glass, the next step is firing it correctly. Think of a firing schedule as a recipe for your kiln—it tells you how hot to get it and for how long. Getting this right is key to a successful project. While every kiln and project is a little different, these resources will give you a solid foundation for creating beautiful, durable fused glass art.

Getting the Most from Manufacturer Guidelines

The single most important rule in glass fusing is to follow the manufacturer’s guidelines. Each type of glass, whether it’s COE 90 or COE 96, has a recommended firing schedule designed to get the best results. Sticking to these instructions is your best defense against common problems like cracking or incomplete fusing. Before you even think about turning on your kiln, find the specific recommendations for the glass you’re using. This simple step will save you a lot of time, materials, and frustration down the road.

Sample Firing Schedules for COE 90 and 96

Because COE 90 and COE 96 glass have different chemical makeups, they require different firing times and temperatures in the kiln. You can usually find detailed firing guides on the glass manufacturers’ websites, which are an excellent starting point. These schedules will give you specific temperature targets and hold times for each stage of the fusing process, from the initial heating to the final annealing. Use these as your baseline, and remember that you may need to make small adjustments based on your specific kiln and the size of your project.

The Best Way to Document Your Kiln Tests

To really understand how your glass behaves, it’s helpful to document your tests. This doesn’t have to be complicated. You can analyze your fused test pieces using two polarized lenses to check for stress, which can show you if your annealing schedule was successful. Some artists also use tools like a ‘Fuse It Test card’ to see how different temperatures affect the glass. Taking notes on what you see helps you analyze the results of your experiments and fine-tune your firing schedules for future projects.

Why You Need a Glass Fusing Journal

A project journal is one of an artist’s best tools. Before you commit to a large piece, it’s always a good idea to run small test pieces to make sure everything fuses as expected. Use a simple notebook to jot down the type of glass you used, the firing schedule, and the final result. Did the colors stay true? Was the fuse level what you wanted? Keeping a journal helps you track your findings, repeat your successes, and learn from any pieces that didn’t quite turn out. Over time, this log will become your personal guide to glass fusing.

Frequently Asked Questions

I have a bunch of scrap glass and I’m not sure what COE it is. Can I still use it? It’s best to avoid using mystery glass in any project you care about. The easiest way to prevent this issue is to get into the habit of labeling your glass and keeping your COE 90 and COE 96 scraps in completely separate, clearly marked bins. If you absolutely must identify a piece, you can perform a compatibility test by fusing a small sample to a piece of glass with a known COE and checking for stress lines with polarized lenses.

I’m just starting out with glass fusing. Should I begin with COE 90 or COE 96? There’s no single right answer, as it really comes down to your personal goals and budget. Many new artists start with COE 96 because it tends to be a bit more affordable, which allows for more experimentation without a huge investment. On the other hand, COE 90 is known for its exceptionally wide and unique color palette, which might be more appealing to your artistic style. The most important thing is to pick one system to start with and build your collection from there.

What really happens if I mix a tiny piece of the wrong COE into my project? Even a very small piece of incompatible glass can ruin your entire project. Because the two types of glass expand and contract at different rates, they create immense internal stress as the piece cools. This tension will almost always cause the glass to crack. The break might happen right away in the kiln, but it can also happen days, weeks, or even a year later, acting like a ticking time bomb in your finished art.

Can I use the same firing schedule for both COE 90 and COE 96 glass? No, you need to use different firing schedules for each type of glass. Because they have different chemical properties, they melt, fuse, and cool at different temperatures and rates. Using a schedule designed for COE 96 on a COE 90 project can result in an under-fired piece, while the reverse could cause your design to lose detail. Always refer to the specific firing guidelines provided by the glass manufacturer for the best results.

Is one COE considered higher quality or better than the other? Neither one is inherently “better”—they are simply different systems. Both COE 90 and COE 96 are high-quality materials used by professional artists to create stunning work. The choice between them is based on artistic preference and project requirements. COE 90 offers a vast and unique color range, while COE 96 is known for its brilliant colors and affordability. The best glass is the one that is right for your specific design.