A glass chimney is a tube of glass around the flame that shields it from drafts and creates an updraft, which improves combustion so the flame is steadier, brighter and smokes less. It must sit on a base that lets air in underneath and open at the top so gases escape. A mason jar with the bottom removed or a bottle with its bottom cut off will serve.
Part of Oil Lamp Construction
A glass tube around a lamp flame creates its own updraft, the same principle that drives a stove riser. The draft steadies the flame and improves combustion.
A Chimney Makes Its Own Draft
Hot gases from the flame are lighter than the air around them and rise through the tube, pulling fresh air in at the bottom. The overview lists what a chimney does:
- Protects the flame from drafts, so it does not flicker or blow out.
- Creates an updraft that improves combustion, giving less smoke and a brighter flame.
The same updraft principle drives stoves; see The Chimney Effect.
Method: Cutting A Bottle
The overview’s method is: wrap a cotton string soaked in alcohol around the bottle at the desired cut line, light it, let it burn out, then immediately plunge the bottle into cold water. The thermal shock makes a clean break.
Step 1: Set up outdoors on bare ground, away from anything that burns, with a bucket of cold water within reach.
Step 2: Protect yourself. Wear eye protection and leather gloves. Glass may fly.
Step 3: String. Wrap the string snugly around the bottle on the cut line. Wring out the string so it is damp with alcohol, not dripping, and keep the alcohol container well away and closed before you light.
Step 4: Burn and plunge. Light the string, turn the bottle slowly, and when the flame goes out plunge it into the water.
Step 5: Finish. Smooth the cut edge with wet sand or a stone until it no longer cuts.
Fitting The Chimney
- Raise it on a base with gaps or on metal clips so air reaches the flame from below.
- Keep the flame small so glass does not overheat. Everyday bottle and jar glass tolerates heat gradients poorly.
- Do not splash cold water or put a cold object on a hot chimney.
- Do not use a chimney with chips or hairline cracks.
Common Mistakes
- Sealing the base of the chimney against the lamp. The flame starves, smokes and can make carbon monoxide.
- Using a chimney that is too narrow. The flame touches the glass and soots it.
- Cleaning a hot chimney. Wait until it is cold; wipe off soot.
Safety
Fire, glass and incomplete burning
Alcohol is a flammable liquid with a flash point near room temperature, and the cut can shatter glass. Work outdoors, with eye protection, gloves and water ready. If the chimney blackens with soot the flame is burning incompletely and making carbon monoxide, which has no smell: turn the wick down and ventilate with an inlet and an outlet.
What’s Next
- Learn next: Multiple Wicks — more flame, more fuel
- Combine with: The Chimney Effect — the draft idea behind both