Lampworking shapes glass tubing in a focused flame, historically an oil lamp with forced air, now a gas or alcohol burner fed by a foot-operated bellows, with the flame reaching 1,000-1,200 °C. The basic operations are bending, drawing, cutting, joining, bulb forming and sealing. Because a bench flame heats only a small zone, each operation is a local softening, and every finished piece still needs annealing.
Part of Glass Blowing and Forming
Shaping glass tubing with a small torch at a bench instead of in a furnace.
Lampworking Trades A Furnace For A Flame And A Small Heated Zone
The furnace methods hold a whole mass of glass at working temperature. A lampwork flame softens a few centimetres of tube while the rest stays rigid, which is why tube can be bent and sealed without being gathered. The carrier gives the setup: a gas or alcohol burner with a foot-operated bellows supplying forced air, a flame reaching 1,000-1,200 °C.
That range overlaps the working ranges of soda-lime (900-1,050 °C) and borosilicate (1,100-1,250 °C) from the carrier’s table, but borosilicate’s range reaches above the flame’s top figure of 1,200 °C by 50 °C (1,250 − 1,200); a flame at the low end will work soda-lime only. If the burner cannot reach 1,100 °C, borosilicate tube will not soften enough to work.
What You Need
- A burner: gas or alcohol, with a nozzle that takes forced air.
- A foot-operated bellows to free both hands; see Bellows Building.
- Tubing: see Glass Tube Drawing.
- A file for scoring, a rest to lay hot glass on, and an annealing oven.
- Eye protection with a dark tint.
Method: The Six Basic Operations
Bending. Heat a section, bend to the angle you want and hold until it is rigid.
Drawing. Heat and pull to reduce the diameter.
Cutting. Score with a file and snap.
Joining. Heat two tube ends, press them together and blow slightly to restore the bore.
Bulb forming. Seal one end, heat a section, blow to create a bulb. This is how flasks are made.
Sealing. Heat the end and draw it closed.
After each: rotate continuously so the heated zone does not sag, and anneal the finished piece.
Worked Example
Heat balance is the limit on tube size, but the corpus has no heat figures for a burner. The one number that can be checked is the flame itself: for borosilicate, the working range bottom is 1,100 °C, so a burner that gives only 1,000 °C falls 100 °C short of it. Soda-lime’s top is 1,050 °C, so a 1,000 °C flame is 50 °C short of the very top, but inside the range. Ask the burner for temperature, not just for a flame.
Common Mistakes
- Working a cold section. Glass cracks when forced.
- Heating a thick wall on one side only. The tube cracks along the heated line.
- Letting a hot seal cool in open air. Put it straight into the oven.
- Forgetting that a closed bulb is a pressure vessel when it is heated again.
Safety
Hot glass does not look hot
Tube that has just come out of the flame is below about 600 °C within seconds and looks like cold tube; a bench of tubing mixes hot and cold pieces indistinguishably. Keep a hot rest, and do not pick up a piece you did not just put down.
Fuel, alcohol flames and fumes
A spirit burner can burn with a nearly invisible flame in daylight (recalled general fact, not from the corpus), so a worker can place a hand in it. Keep fuel containers away from the flame, refill only when cold, and never refill a burner that is lit or hot. Work in ventilated space.
What’s Next
- Learn next: Joining and Sealing — leak-tight joints
- Combine with: Laboratory Glassware — the items to make