Glass Furnace
The melting tank that holds glass at working temperature, day and night, for the whole life of the studio.
Gathering
| Chamber volume | 60 - 400 L |
|---|---|
| Maximum temperature | 700 °C |
| Control accuracy | plus or minus 2 °C |
| Stored programs | 20 |
| Insulation | Low mass fibre board, 100 - 150 mm |
| Supply | 230 V single phase or 380 V three phase |
Compatible glass types
Soda-lime
Borosilicate
Lead crystal
Compatibility assumes the tool is rated for the working temperature of that glass family. Check the maker's documentation before use.
Overview
An annealing oven, sometimes called a lehr or a front-loading kiln, holds a piece in the annealing range long enough for internal stress to relax, then cools it slowly enough that no new stress forms. The chamber is insulated on all six faces and controlled by a programmer rather than a simple thermostat, because the cooling rate matters far more than the top temperature.
Safety notes
- The door face stays hot for hours after the program ends. Post a cooling notice rather than relying on memory.
- Never open the door mid-program. A rush of cold air will crack everything inside.
- Place a physical barrier or keep the kiln in a closed room when children or visitors are present.
Using it well
Practical guidance
- Load the oven while it is still at annealing temperature. A cold kiln plus a hot piece is a guaranteed crack.
- Leave a minimum of 25 mm between pieces so air can circulate around each one.
- Record every program run. When a piece cracks, the schedule log is the only evidence you have.
What to look for
- Six-sided insulation with a low thermal mass
- Sheathed elements that do not radiate directly onto the work
- Viewing port with a heat shield
- Type K thermocouple with cold junction compensation
Reference information only. Specifications are published ranges drawn from manufacturer documentation and normalised for comparison. They vary between makers and between individual units. This page does not sell or endorse any product, and does not guarantee any result. Follow the equipment manufacturer's instructions and take hands-on instruction before operating hot glass equipment.
Related
Tools used alongside the annealing oven
Glory Hole
A reheating chamber that brings a cooling piece back to working temperature without touching the main furnace.
Shaping / Blowing
Kiln Controller
The programmer that executes a ramp-and-hold schedule and holds the furnace to it.
Annealing
See the furnace & heating workflow
Read the category overview, or jump into the 3D Studio to see these tools applied to a live piece.