Flamework & Borosilicate Glass

What It Is

In flamework, glass rods and tubes are heated in a torch flame until soft, then shaped using gravity, breath, and hand tools. The torch produces a flame from approximately 1,200–3,000°C depending on fuel mixture (propane/oxygen, natural gas/oxygen). The artist manipulates the softened glass in real time — pulling, winding, fusing, and sculpting.

Glass Types — COE Compatibility

COE (Coefficient of Expansion) measures how much glass expands when heated. Glass types with different COEs cannot be fused together — as they cool, they contract at different rates, creating internal stress that causes cracking.

• COE 33 — Borosilicate (Pyrex-type): High thermal shock resistance, high strain point (~760°C), requires very high flame temperature. Ideal for large sculptural work, scientific glass, hollow forms. Used at Berlin Flame Studio.
• COE 104 — Soft glass / Soda-lime: Lower working temperature, more accessible for beginners, commonly used in bead-making. Cannot be combined with COE 33.
• Scientific glass: Borosilicate glass used in laboratory equipment — rods, tubes, flasks. The same glass type used for flamework sculpture, worked with the same torch techniques.

Tools

• Bench torch (minor burner for COE 104; larger surface mix torch for COE 33)
• Didymium / Sodium flare glasses — eye protection specifically for flamework (blocks sodium flare from molten glass)
• Graphite marver (flat shaping surface)
• Tweezers, jacks, tungsten picks
• Annealer or kiln (mandatory for thick pieces)
• Kiln brick or fiber blanket (for temporary holding during work)

Process

1. Heat the glass rod/tube in the outer flame first — introduce gradually to avoid thermal shock.
2. Move into the working area of the flame. The glass will become orange, then clear and flowing.
3. Shape using tools, gravity, and rotation. Work quickly — borosilicate stiffens rapidly as it moves away from the flame.
4. Reheat as needed. Do not let the piece cool unevenly — this causes stress cracks.
5. Anneal: place in a hot kiln (at annealing temperature) immediately after completing the piece. Never put hot glass on a cold surface.

Common Failures

• Thermal shock cracking: Glass introduced to flame too quickly, or cooled too rapidly. Always preheat slowly in the outer flame.
• Compatibility cracking: Mixing COE 33 and COE 104 glass. Use only compatible glass types in one piece.
• Devitrification (going white/cloudy): Glass held at a temperature range where crystallization begins (~700–800°C for borosilicate). Move through this range quickly — either hotter or cooler.
• Bubbles: Contamination from foreign material, or too-rapid temperature change creating trapped air.

Jay's Studio Note

The specificity of borosilicate at the flame — the way it resists heat longer than soft glass, then suddenly flows — requires a different quality of attention than other hot materials. You cannot rush borosilicate. You move slowly into the flame, slowly out, and slowly into the annealer. The pace is set by the material, not the maker. Berlin Flame Studio's studio environment (Berlin, 2024) introduced this as a contemplative as much as technical practice.

References

• Berlin Flame Studio, Berlin — borosilicate flamework