By the UK Glass Kiln Hub — Expert Reviews & Guides for Home Glassblowers Team · Updated May 2026 · Independent, reader-supported

How to Fire Fused Glass at Home in the UK — Step-by-Step Firing Guide

Fused glass is deceptively rewarding: two pieces of compatible glass, stacked together, transformed into a single unified work inside your kiln. But getting the firing right separates the successful pieces from warped disappointments. Unlike torch work or stained glass, fusing demands precision — precise temperatures, precise ramp rates, and precise hold times. This guide walks you through the three main firing types you'll use at home, with schedules scaled for UK domestic kilns.

What You Need Before You Start

Before setting a single schedule, verify three essentials. First, your glass must be compatible. Standard soda-lime fused glass works fine; mixing borosilicate (high-fire) with soda-lime (low-fire) causes cracking because they expand and contract at different rates. Second, your kiln must have a kiln wash applied to the shelves and walls — unglazed kiln wash powder mixed with water creates a barrier that prevents glass from fusing permanently to your shelves. Third, use kiln shelf paper (a thin ceramic liner) beneath your pieces; it makes cleanup easy and reduces the risk of glass sticking even if your kiln wash wears thin.

The Three Core Firing Programmes

Full Fuse

A full fuse creates a single, seamless piece. The glass slumps slightly into a combined shape, and any air gaps between layers are eliminated. Use this when you want pieces to bond completely.

Full Fuse Schedule (220V kiln, 1 kWh nominal):

• Room temperature to 260°C at 200°C/hour (gentle warm-up over 1.3 hours, prevents thermal shock)
• 260°C to 700°C at 200°C/hour (2.2 hours)
• 700°C to 790°C at 50°C/hour (1.8 hours — slow final approach to fusing temperature)
• Hold at 790°C for 30 minutes
• Cool naturally to 600°C (no forced cooling)
• 600°C to room temperature at 100°C/hour (allow 6 hours — slow cool prevents cracking)

Total time: approximately 12–14 hours. Your kiln's insulation affects actual time; older kilns may take longer.

Tack Fuse

Tack fusing bonds pieces just enough to hold their shape during handling and further work. Layers stay partially separate, preserving individual glass colours and textures. This is your go-to for layered designs and production pieces.

Tack Fuse Schedule:

• Room to 260°C at 200°C/hour
• 260°C to 700°C at 200°C/hour
• 700°C to 760°C at 50°C/hour
• Hold at 760°C for 15–20 minutes
• Cool naturally to 600°C
• 600°C to room temperature at 100°C/hour

Total time: 8–10 hours. You'll notice the lower peak temperature (760°C versus 790°C) and shorter hold time; that's the entire difference. Tack fuse is fast enough for batch production.

Slump Fuse

Slumping happens after fusing — it's a separate firing where you drape or press already-fused glass into a mould. The glass must be soft enough to move but not so hot it flattens completely.

Slump Schedule (into a shelf mould):

• Room to 260°C at 200°C/hour
• 260°C to 650°C at 150°C/hour
• 650°C to 700°C at 30°C/hour (slow, controlled approach)
• Hold at 700°C for 10–15 minutes (watch your piece; stop holding when it matches your mould shape)
• Cool to 600°C naturally
• 600°C to room temperature at 100°C/hour

Total time: 6–8 hours, depending on how much slumping you want. Slumping is the most visual firing — you can load the kiln and watch your pieces settle into shape. Higher temperatures cause excessive slumping and uneven results.

Step-by-Step Firing Process

1. Prepare your shelf. Clean it, apply kiln wash if needed (once per 5–10 firings depending on wear), and lay kiln shelf paper flat. Smooth out creases; trapped air beneath the paper can cause uneven heating.

2. Stack and stack cleanably. Place your bottom layer of glass directly on the shelf paper. Add a tiny spacer — a grain of kiln wash or a small ceramic pin — between pieces if you're stacking multiple layers and want them fully separate. If you want pieces fused together but not to the shelf, keep a 5 mm margin around the edges and don't let glass touch the kiln walls.

3. Load your kiln. Centre your piece. Never place glass on the very edge of a shelf — heat distribution is poor there, and you risk uneven fusing. Leave at least 2–3 cm clearance from the kiln sides and heating elements.

4. Set your programme. If your kiln has a digital controller (most UK domestic kilns do), enter the full schedule. If it's a basic kiln with a manual pyrometer, you'll need to adjust heating manually or install a kiln sitter and timer as a backup. Manual kilns are harder to dial in and less reliable for fusing.

5. Fire and don't open the door. Once you've started the programme, resist opening the kiln door to check on progress. Opening causes heat loss, thermal shock to your glass, and uneven firing. The only exception is slump firing, where brief peeks (after 20+ minutes into the hold phase) are acceptable to gauge shape.

6. Cool slowly. This is critical. Pulling your finished piece out whilst still warm causes cracking. If your kiln has a soaking feature, use it; if not, simply turn off the kiln and let it cool over 6+ hours. You can open the door once the kiln is below 60°C.

Troubleshooting Firing Issues

Pieces don't fuse together: You probably stopped 10–20°C short of proper fusing temperature. Soda-lime glass fuses reliably at 790°C for a full fuse; if your kiln's actual temperature runs cooler than the readout, raise peak temperature by 5–10°C and try again.

Glass cracks after cooling: Uneven cooling or thermal shock during firing. Ensure your cool-down rate is 100°C/hour or slower from 600°C downward. Check that you're not opening the kiln door whilst it's hot.

Wavy or distorted edges: You've exceeded your target hold time or temperature. Pieces slump progressively; hold 760°C for 30 minutes and you've overcooked a tack fuse. Use a timer and stick to it.

Glass sticks to the shelf: Your kiln wash has worn through or isn't thick enough (should be 2 mm minimum). Reapply a fresh coat and use kiln shelf paper on top.

A Note on Kiln Choice

Most UK domestic kilns sold for fusing are 220V, 1–2 kWh capacity, and reach 1000°C+ comfortably. If you're buying a first kiln for fusing only, look for one with a built-in digital controller; the reliability gain justifies the cost. Manual kilns work, but dialling in schedules is tedious and success rates are lower.

Firing fused glass at home is entirely manageable once you follow a consistent process. Your first pieces might need a restart (that's normal), but by your third or fourth firing, you'll see the pattern. Stick to the temperatures and ramp rates above, don't rush the cool-down, and you'll get repeatable, professional results from a home setup.