Glory Hole

Specifications

Opening diameter

150 – 300 mm

Operating temperature

1150 – 1300 °C

Chamber depth

300 – 500 mm

Heat source

Gas burner, often with forced air; electric on small units

Recovery time

10 – 40 s to bring a gather back to working temperature

Body

Steel shell lined with insulating firebrick and a hot-face castable

Working height

Set to the operator — usually 950 – 1100 mm to the sill

Technical parameters

Burner

Single or twin, with air/gas proportioning for an oxidising flame

Atmosphere

Must run oxidising or neutral; a reducing flame will grey the glass

Door

Sliding or hinged, to keep the chamber hot when not in use

Rotation rest

A pair of rollers or a yoke in front, so the pipe keeps turning

Floor

A flat sill that will not catch the pipe as it rolls

Cost band

Medium — cheaper than the furnace, used far more often

Overview

A glory hole is an open-fronted reheating chamber, hotter than the furnace and used constantly. Glass loses workability within seconds of leaving the furnace, so the rhythm of a hot shop is a loop: shape at the bench, reheat at the glory hole, shape again. The glory hole runs hotter than the furnace because its job is to bring the surface of a cooling piece back up fast, without heating the whole piece through.

Where it fits in the process

Glory Hole is used in shape, blow, color. The stage decides how hot the glass has to be when the tool touches it, which in turn decides how much of the work it can do in one pass.

Safe use

• The glory hole mouth is the brightest and hottest thing in the studio. Never look into it without appropriate eye protection.
• Radiant heat from the open mouth burns skin at a distance. A heat shield belongs on every pipe.
• A piece reheated too fast will crack. Watch the surface, not the clock.
• Keep the front sill clear. A pipe rolled into a stray tool will take the piece off the end.

How it is used

1. Run the glory hole oxidising. A reducing flame deposits carbon and greys a clear glass permanently.
2. Reheat little and often rather than long and rarely. Fast surface reheats keep the interior stable.
3. Keep the pipe rotating whenever the piece is in the chamber. A stationary piece slumps.
4. Never put a piece into the glory hole wet. Any water on the surface will spall the glass.
5. Set the height once for your body and mark it. Reaching up or down all day is what wrecks a shoulder.

Compatible glass types

Matching the tool to the glass family matters less than matching the glass to itself — see the COE compatibility calculator before combining two glasses.