Glass fusing and slumping are some of the most captivating techniques in kilnforming, but the real magic happens inside the kiln, where temperature, timing, and patience converge. Understanding your kiln firing schedule is critical for achieving strong, beautiful, and structurally sound glasswork.

At Make Santa Fe, we want every member to feel confident working in the glass studio. Based on Bullseye Glass’s industry-standard research, this guide breaks down how and why different firing schedules work and how to adjust them for your project.

🔥 What Is a Firing Schedule?

A kiln firing schedule is a series of temperature changes — how quickly you heat or cool your glass, how long you hold it at specific points, and when to let it rest. Each step affects the piece’s final look, strength, and stability.

Bullseye Glass recommends thinking of your firing schedule as eight stages:

1. Initial Heat (room temp to 1000°F)
2. Pre-Rapid Heat Soak (optional, around 1225°F)
3. Rapid Heat (to process temp)
4. Process Soak (tack, slump, or full fuse)
5. Rapid Cool (down to anneal temp)
6. Anneal Soak (usually at 900°F)
7. Anneal Cool (900°F to 700°F)
8. Final Cool to Room Temperature

Each stage is carefully designed to avoid cracking, stress, devitrification (crystallization on the surface), or trapped bubbles.

🧩 Tack Fusing (1290–1435°F / 699–779°C)

Tack fusing joins pieces of glass just enough to stick them together while retaining their original shape and texture. Edges soften, surfaces may gloss over, but the glass doesn’t flatten.

Use it when:

• You want texture or dimension
• Working with layered designs or decorative elements

Common signs of a tack fuse:

• Edges round but footprint remains
• Surface tension begins to pull glass together
• Devitrification risk starts to increase after ~1350°F

📌 Example hold: 10–20 min at 1375°F (depending on glass and desired texture)

🌊 Full Fusing (1480–1550°F / 804–843°C)

Full fusing melts multiple layers into a single, flat, unified piece. This is the ideal choice for functional or smooth decorative objects like coasters, jewelry, or blanks for slumping.

What happens:

• Glass flows into a single thickness (~6mm if unconstrained)
• Surface becomes smooth and glossy
• Air between layers can expand and rise — timing is crucial

📌 Typical hold: 10–15 min at ~1490°F; adjust based on glass thickness and kiln behavior

🥣 Slumping (1100–1300°F / 593–704°C)

Slumping involves taking a pre-fused piece and reheating it just enough to let gravity gently shape it into a mold.

What to watch for:

• Too hot = over-melt and loss of form
• Too cold = glass won’t fully settle into the mold
• Mold type and shape affect results

📌 Soak temp: usually 1200–1250°F, held for 10–20 minutes or until desired shape is achieved

🧠 Heatwork: It’s About Time and Temp

Bullseye emphasizes that glass behavior is based on heatwork — a balance between temperature and time. You can get similar results from:

• Lower temperatures held longer
• Higher temperatures held shorter

This interplay means no single “magic number” — every project may need small adjustments.

Sample Schedule: Full Fuse

🧼 Safety Tips & Studio Best Practices

• Always wear PPE: eye protection, heat-resistant gloves, and a mask when handling powders or frit
• Never open the kiln above 500°F — this can cause thermal shock and injury
• Clean shelves and molds properly — devitrification is more likely on dirty or contaminated surfaces
• Keep a firing log: track your kiln, your setup, and your results

📍Learn with Us at Make Santa Fe

Firing glass is both an art and a science; the best way to learn is by doing. Join a Glass Fusing or Kiln Badge class, or ask about our open studio sessions where you can experiment safely with the support of staff and fellow makers.

• 👉 View Upcoming Classes
• 👉 Explore Track Courses
• 👉 Become a Member

✨ Final Thought

When you understand your firing schedule, you unlock a new world of precision and possibility in kiln-formed glass. Whether you’re going for texture, flow, or form, it all starts with the right timing.