Activity 001: Kiln Fusing — Designing and Firing a Fused Glass Tile

Activity ID: U12M3-ACT-001 Duration: 45 minutes (plus kiln firing time outside class)

Overview

Students design a small fused glass tile using pre-cut soda-lime glass pieces, prepare the kiln for firing, program a complete fusing schedule, and load their project. This activity applies knowledge of CTE compatibility, kiln preparation, firing schedules, and annealing to produce a finished full-fused piece. Kiln firing occurs outside class time; results are reviewed in the following session.

Materials & Equipment Needed

• Pre-cut soda-lime glass pieces (tested compatible, same COE 90 or COE 96):
• Base pieces: 4" x 4" clear, 3mm thickness (one per student)
• Accent pieces: assorted colors, pre-cut shapes (strips, circles, triangles)
• Programmable kiln with digital controller
• Kiln shelves (clean, properly sized)
• Kiln wash (alumina hydrate) and brush (if shelves need re-coating)
• Kiln shelf paper (fiber paper) — alternative to kiln wash
• Kiln posts/stilts for shelf positioning
• Isopropyl alcohol and lint-free cloths for cleaning glass
• Tweezers for positioning small pieces
• Firing schedule worksheet (one per student)
• Kiln log sheet (shared)
• Safety glasses
• Thermal gloves (for kiln loading if kiln is warm)
• IR-rated safety glasses (for kiln viewing)

Instructions & Procedure

Part 1: Design and Glass Preparation (15 minutes)

1. Students sketch their tile design on paper at actual size (4" x 4")
2. Select accent pieces that complement the design — instructor confirms all pieces are compatible (same COE)
3. Clean ALL glass pieces with isopropyl alcohol and lint-free cloth:
4. Both sides of every piece
5. Allow to dry completely
6. Handle only by edges after cleaning (fingerprints cause devitrification)
7. Arrange accent pieces on the clear base piece according to the design
8. Verify no pieces extend beyond the base edges (overhang causes uneven fusing and shelf contamination)

Part 2: Kiln Preparation (10 minutes)

1. Inspect kiln shelf for cracks, old kiln wash buildup, or glass residue
2. If shelf needs re-coating: apply three thin crossed layers of kiln wash, allow to dry between layers
3. Alternative: place fiber paper (shelf paper) on shelf — cut to size, no overlap
4. Position kiln shelf on posts at appropriate height (centered in kiln, away from elements)
5. Instructor demonstrates kiln loading:
6. Place shelf with kiln wash/paper
7. Position prepared tiles on shelf with 1-inch spacing between projects
8. Close kiln lid carefully — do not bump loaded pieces

Part 3: Firing Schedule Programming (15 minutes)

1. Students complete the firing schedule worksheet for a standard full fuse:

Segment	Rate	Target Temp	Hold Time	Purpose
1	300°F/hr	1000°F	0 min	Initial ramp — prevent thermal shock
2	400°F/hr	1250°F	0 min	Process ramp through softening range
3	400°F/hr	1375°F	20 min	Bubble squeeze — release trapped air
4	AFAP	1490°F	10 min	Full fuse — pieces merge completely
5	AFAP	960°F	30 min	Crash cool to annealing point, then soak
6	100°F/hr	800°F	0 min	Critical cool — prevent stress formation
7	300°F/hr	100°F	0 min	Final cool to room temperature

1. Instructor reviews each student's worksheet and discusses modifications:
2. Why is segment 5 a crash cool? (Minimize devitrification zone time)
3. What would happen if we cooled at 300°F/hour through the critical range?
4. How would this schedule change for a 12mm thick piece?
5. Instructor programs the kiln controller with the agreed schedule
6. Students record the schedule and expected total firing time in the kiln log

Part 4: Results Review (following session)

1. After kiln has cooled to room temperature, instructor removes pieces with thermal gloves
2. Students examine their finished tiles and evaluate:
3. Is the fuse complete? (Smooth surface, no visible seams)
4. Any devitrification? (White haze or scummy patches)
5. Any bubbles? (Trapped air pockets)
6. Any cracking? (Thermal stress or CTE issues)
7. Does the piece match the original design intent?

Discussion Points

• Why must the kiln cool to room temperature before opening, even though the glass looks solid at 400°F?
• What visual differences would you expect between a tack fuse and a full fuse of the same design?
• If your tile has devitrification on the surface, what would you change in the firing schedule?
• Why is the bubble squeeze segment placed before the full fuse temperature rather than after?
• How does the 6mm rule affect your design decisions?

Expected Outcomes

• Students produce a fully fused 4" x 4" glass tile with smooth surface and no visible defects
• Students can write a complete firing schedule with appropriate ramp rates, holds, and cooling
• Students understand the purpose of each firing segment and can modify the schedule for different scenarios
• Students demonstrate proper kiln preparation including shelf coating and piece spacing

Assessment Rubric

Criteria	Excellent (4)	Proficient (3)	Developing (2)	Beginning (1)
Firing schedule	Complete, accurate schedule with all segments justified	Schedule complete, minor errors in rates or holds	Missing segments or incorrect temperatures	Unable to construct a firing schedule
Glass preparation	All pieces cleaned, compatible, properly arranged	Mostly clean, minor handling after cleaning	Some pieces not cleaned, arrangement issues	Pieces contaminated or incompatible glass used
Kiln preparation	Shelf properly coated, correct height, pieces spaced	Minor issues with shelf prep or spacing	Shelf coating inadequate or pieces too close	Kiln prep steps skipped or incorrect
Results analysis	Correctly identifies all success/failure indicators	Identifies most indicators, minor misdiagnosis	Partial analysis, some factors missed	Unable to evaluate finished piece

Safety Considerations

• Wear safety glasses when handling glass pieces throughout the activity
• Clean glass with alcohol in a well-ventilated area — alcohol is flammable
• Wear thermal gloves when loading a warm kiln or handling recently fired pieces
• Wear IR-rated safety glasses when viewing kiln interior during or after firing
• Never open the kiln above 200°F — thermal shock will destroy pieces and hot air rushes out
• Do not touch kiln exterior during firing — surfaces may be extremely hot
• Only the instructor operates the kiln controller and loads/unloads the kiln

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Last Updated: 2026-03-19