Your first week of glass fusion

Glass fusion's learning curve is mostly about the kiln — understanding firing schedules, COE compatibility, and what heat does to glass. Here's how your first week actually goes, from your first score to your first successful firing.

By The JustBeginning Editors · Published June 1, 2026

Glass fusion has a reputation for being intimidating — kiln, compatible glass, ramp speeds, annealing. The terminology sounds like chemistry class. But the actual experience of your first week is simpler than the vocabulary suggests. Most of what you need to understand fits in a single afternoon of reading, and the rest you learn by doing.

Here’s what your first week actually looks like, day by day, with the decisions that matter and the things you’ll be tempted to worry about but shouldn’t.

Day 1–2: Understand COE before touching a kiln

The single most important thing to get straight before buying anything is COE compatibility. COE stands for Coefficient of Expansion — it’s a measure of how much glass expands when heated. Every piece of fusible glass is manufactured to expand at a specific rate, and glass from different COE systems expands at different rates.

The two systems you’ll encounter are COE 90 and COE 96. They are not compatible. Put COE 90 and COE 96 glass in the same piece, fire it, and the stress from unequal expansion will crack the piece — sometimes immediately, sometimes days later as the glass continues to settle. Pick one system before you buy a single sheet of glass, and commit to it.

Which one? For most beginners, COE 96 (formerly called System 96, now carried primarily by Oceanside and Wissmach) is slightly easier to find at craft stores and online retailers. COE 90 — associated with Bullseye Glass Co. — has a larger selection and a deeper community of resources, but it’s harder to find on short notice. Either is a fine choice; the commitment is what matters.

Once you’ve chosen, make a simple rule for yourself: everything in your studio is one COE. No exceptions, no “just this one piece.”

Day 2–3: Your first cuts

Glass cutting is less scary than it looks, and more precise than it feels at first. The tool is a glass cutter — a small handheld wheel that scores a line into the surface of the glass. You then flex the glass slightly along that score line and it snaps cleanly along the path.

A few things make the difference between a clean break and a disaster:

Score once, firmly. Run the wheel from edge to edge in a single continuous stroke with consistent pressure. If you hear the wheel grinding rather than a clean scratching sound, you’re pressing too hard. The score should sound like a zipper being pulled. If you hesitate or lift mid-stroke, you’ll get a jagged break.

Break immediately. Don’t let a scored piece sit for more than a few minutes — the score can heal slightly as stress redistributes. Score, then snap.

Use running pliers for straight breaks. Center the pliers over the score line and squeeze gently until the glass snaps. You’ll feel it give before it breaks. It’s satisfying in a way you don’t expect.

For your first projects, stick with straight cuts. Squares, rectangles, triangles. Curves come later. The goal in your first week isn’t to make beautiful shapes — it’s to understand how the glass behaves.

Day 3–5: Understanding firing schedules

A kiln schedule is the recipe that tells your kiln how fast to heat up, how long to hold at peak temperature, and how to cool down. Get it right and you get a beautiful, stress-free piece. Get it wrong and you get cracking, devitrification (a milky haze on the surface), or an underworked piece where the glass didn’t fully fuse.

The basic schedule for a full fuse has four phases:

1. Ramp up — heat climbs at a controlled rate (usually 300–500°F per hour for thin pieces). Heating too fast can crack cold glass.
2. Process temperature hold — for a full fuse, this is typically around 1480–1500°F held for 10–20 minutes, until the glass edges round and the pieces merge completely.
3. Flash cool — drop temperature quickly to around 1050°F to stop devitrification.
4. Anneal and slow cool — hold at ~1000°F for 30–60 minutes to relieve internal stress, then drop to room temperature at 100°F per hour or slower.

Your kiln almost certainly came with a programmable controller. Enter this schedule as a program before your first firing. Bullseye and Warm Glass both publish free firing schedules online; start with one of their beginner templates rather than trying to write your own.

One rule above all others: don’t open the kiln until it’s fully cooled. Room temperature. If you open it at 400°F because you’re curious, the sudden temperature shock will crack your piece. A fully programmed anneal-and-cool cycle takes 8–12 hours. Do something else while you wait.

Day 5–7: Your first firing

Before you load the kiln, make sure:

• Thinfire shelf paper is cut to size and laid under every piece
• Pieces are clean and free of fingerprints (oils can cause surface defects)
• Glass pieces are arranged and designed — once the kiln closes, you’re committed
• Safety glasses are on whenever you’re handling raw glass

Load the kiln, close it, start your program. Walk away. The hardest part of glass fusing is not interfering.

When the kiln has cooled to room temperature — open it slowly. The transformation is genuinely astonishing the first time. Edges that were sharp and angular are now soft and rounded. Colors have shifted slightly, deepened. The pieces have merged into something that looks like it was always one object.

You’ll notice a few things:

• Edges are soft — this is correct and beautiful for a full fuse
• Surface might be slightly textured — depending on how you prepped the glass and how long you held at temp
• Color may have shifted slightly — some colors are affected by the firing atmosphere; this is normal and part of the medium

Your first piece will probably surprise you — either better than you expected, or with a specific flaw you now know how to fix. That’s exactly right. Glass fusing teaches you through each firing.

The mistakes everyone makes

Every beginner hits the same set of problems. You will too. Knowing them in advance doesn’t prevent them, but it takes the sting out:

• Mixing COE accidentally. You buy a beautiful sheet of glass without noticing it’s a different COE than the rest of your stock. It cracks. Label everything. If you don’t know the COE, don’t fuse it.
• Rushing the cool. Opening the kiln too early is the most common way to crack a finished piece. Your kiln is programmed to do this correctly — trust the program.
• Trying curves too early. Tight curves require a grinder and a lot of practice. Stick to straight cuts for your first 10–15 pieces.
• Firing pieces that aren’t flat. Thick glass stacked unevenly creates uneven stress. Aim for uniform thickness across each piece until you understand how glass moves in the kiln.

None of these mistakes are disasters. You lose a piece, you learn something specific, you fire again.

What you have after one week

After seven days of cutting and one or two firings, you’ll have:

• A clear understanding of COE compatibility (the single skill that separates beginners from crashers)
• Decent control over straight cuts and basic shapes
• One or two finished fused pieces — probably small, probably asymmetrical, probably genuinely beautiful

You’re not a skilled glass fusionist yet. You’re something more useful: someone who understands what the kiln is doing and why, and can now start developing real intuition through repetition.

The medium rewards patience and iterative improvement in a way that’s unusual — every firing is a small experiment, and every experiment teaches you something specific about how glass, heat, and time interact.

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Ready to buy your kiln, glass, and supplies? See our glass fusion gear guide for exactly what to get first, what to skip, and how much to budget.