Fusing Method

Fusing glass in a kiln is a fascinating technique that enables artists to create unique and gorgeous projects. The following fusing rules and firing instructions should provide you with enough information to make a variety of projects, creating an appreciation for the complexities and potential of fused glass, and paving the way for more intricate designs and ideas.


Tested Compatible

When glass is heated inside a kiln it expands, and when it cools it contracts. When fusing two or more pieces of glass together, they need to expand and contract at the same rate. Otherwise, when the glass cools, one glass will pull on the other and cause the piece to crack along the seam. Even if the glass survives the cooling process, there is still a risk it might still crack if you try to reheat it in a kiln or even place it in a sunny window. Stress from incompatible glass is always in the piece. Do not try to refire broken incompatible glass.

  • All glass has a coefficient of expansion, or COE.
  • Glass manufactured specifically for fusing is often "tested compatible," or guaranteed to be a certain COE.
  • The most popular fusing glasses are either 90 COE (Bullseye, Uroboros and Wasser) or 96 COE (Spectrum and Uroboros).
  • Always use compatible glass, which is known to have the same COE.


Slower Is Better

thermal shock glass

  • You can't heat or cool glass too slowly. Going too fast can result in cracked glass or Thermal Shock ( see image to right).
  • A safe rate to heat is 15° per minute (900° per hour), although stacked glass 2" in diameter and smaller can be heated at a faster rate.
  • Slow-cooling of glass or "annealing" depends on the thickness of the glass. If the glass breaks because it was heated too fast; turn off the kiln, allow the glass to cool, push it back together, and try again - at a slower rate. Breaks from thermal shock usually go straight across the piece and have a little hook near the edge. They can usually be repaired by refiring.


Glass Likes To Be ¼" Thick

When heating glass to full fuse, anything with less mass will shrink up, anything with more will spread out. This movement can be controlled somewhat by fusing slower, and not going to full fuse.


All Kilns Are Not Alike

  • There are some variances between kilns, especially mini kilns. Sometimes pyrometers are slightly off, and sometimes current loads vary.
  • Use firing schedules as a guide, but remember to check your piece frequently during fusing, and record changes in schedules as needed.
  • Prepare your kiln by applying kiln wash with a kiln brush. Apply one thin coat in each direction. Don't forget to apply kiln wash to molds, too.


Take Good Notes

  • Use a project log to keep important information about your projects.
  • Keep track of what glass was used, how thick the glass was, the firing schedule and the results.
  • This helps repeat good performances and prevent bad ones.

Fusing Glass

Brittle Zone   brittle     Tack Fuse  tack     Full Fuse  full  


Glass Fusing Stages For Mini Kilns

Common Temperatures Fusing Stage Glass Stages
800º F - 1100º F Brittle Zone Do not open the kiln in this range (photo 1)
1325º F - 1425º F Tack Fuse Edges are soft, glass is stuck together (photo 2)
1425º F - 1600º F Full Fuse Glasses combine, uniform thickness throughout (photo 3)
  Fusing Schedule
Use for table top kilns, pieces 1/4" thick, and 3" - 6" in diameter (larger pieces should be heated and cooled slower to prevent thermal shock.
Dial Setting & Time Kiln Temp. Glass Stage
2 for 20 minutes (check kiln) About 500º F No change in glass
3 for 30 minutes (check kiln) About 1000º F Still no change in glass
4 for 10 minutes (check kiln) About 1500º F Glass should be slightly more than tack fused
4 for 5 minutes (check kiln) About 1500º F Glass should be full fused (see further instructions below)
Once the desired look has been achieved turn off the kiln.
  • To stop the fusing process, flash vent the glass to let the heat out by holding the lid off the kiln about 8 seconds and watching the glass surface turn from orange to blackish (the color will return to the glass as it cools). Repeat the process until the temperature stays close to 1000° when the lid is replaced.
  • Replace the lid and turn kiln on low for 20 minutes. This will keep the kiln approximately 1000 - 1200°, allowing a minimal annealing cycle. Turn off the kiln and cool naturally to room temperature.
If more melting is desired, turn dial to 5, but do not leave kiln.
  • It is easy to over fire glass at this temperature and ruin the piece. Let the kiln heat to 1600° and turn the dial back to 4. This will allow the kiln to get slightly hotter, without continuing to gain heat.
  • Check the piece every 3 minutes and try not to let the kiln go above 1600°. When the desired look is achieved, follow the instructions above.


Suggested Supplies

beginner kit Basic Supplies
Listed with Delphi item numbers for quick reference

#6955 Studio 8 Fusing Beginner Kit (see image to right)
#7441 Ceramic Kiln Shelf - 6"
#7465FM Kiln Wash
#7466 Haik Brush
#FIREUPS Uroboros Fire Ups Glass Pack 90 COE
#S96PACK Deluxe System 96 Sampler Glass Pack 96COE
#STUDIO8 Studio 8 Table Top Kiln (see image to right)
studio 8

Glass Cutting Supplies
#5104 Glass Cutter
#5068 Running Pliers
#5066 Breaker/Grozer Pliers

Variety of Glass Molds
#4269 Stainless Steel Barrette Mold
#40916 Mini Square Plate
#24664 Delphi Studio Essential Casting Molds

Kiln Parts All glass fusing kilns have basically the same parts:

  • Elements (high temperature coiled wire)
  • Firebrick insulation
  • Stainless steel cover
  • Thermocouple (high temperature wires covered by ceramic rings)
  • Pyrometer (temperature read out dial)
  • Infinite Dial Some kilns will simply have an on/off switch. The Studio 8 pictured above has the Infinite Dial.


    contemporary warm glassContemporary Warm Glass #6814
    this full-color, 154 page soft cover reference, is a complete guide to fusing, slumping and kiln-forming techniques. With color photos on almost every page, it will lead you through a solid introduction to all the facets of warm glass, and show you beautiful creations to strive for...and beyond! Featuring beautiful projects by author and glass artist Brad Walker, it will inspire both beginning and advanced artists.


    fused glass handbookFused Glass Handbook #6430
    Fusing guru Gil Reynolds presents 25 projects with easy to follow instructions for mold-making, creating pattern bars, and many other hot glass techniques. Provides mock firing times, firing tables, and valuable firing information to get the most from your kiln. Revised Edition. A Delphi Favorite!


    kiln craft glassKiln Crafted Glass Video #4990D
    Discover how glass shaping techniques developed thousands of years ago have been Put to use by contemporary artists. Observe different stages of the glass melting process. Learn how to turn ordinary glass into beautiful sculpture as well as forming, mold materials, preparation, heating and cooling cycles, and more. Includes example projects ranging from beginner levels to advanced.


Wednesday, November 25, 2015
91 Posts

There are several popular books that provide loads of information to get started fusing - a good book will generally explain firing schedules, glass compatibility, and basic techniques. "Contemporary Fused Glass"

Jennifer Bonesteel

Thursday, July 30, 2015
Delphi Expert
188 Posts
Top Contributor Gallery Artist

@billingsc The fiber rope compresses a bit with the weight of the glass during firing. You might try wrapping the fiber rope in a small piece of shelf paper to help it hold it's shape better. A piece of wire can be used to help push the fibers out of the hole when you're done.


Tuesday, July 28, 2015
1 Post

I want to use the twisted rope to make holes right through my glass, once fused is there an easy way to remove the fired rope from in between the glass. Right now I have put the glass into water and then used a fishing line to try and push strands through.

Jennifer Bonesteel

Friday, February 13, 2015
Delphi Expert
188 Posts
Top Contributor Gallery Artist

@istrobin the back side of the glass - the one that touches the shelf paper, kiln wash or mold - will always come out with a duller, rougher finish than the glass not touching anything else. There is no real way to prevent the glass from dulling where it touches another surface.


Tuesday, February 10, 2015
1 Post

I am new to fusing glass. I have used kiln paper and I have used kiln wash, my pieces come out rough on the back. How do you prevent that from happening/ Thanks

Jennifer Bonesteel

Wednesday, June 25, 2014
Delphi Expert
188 Posts
Top Contributor Gallery Artist

@krbeunkate cutting your clear cap slightly larger than your base is a good idea when working with textures or dichroic glass. A bit of fusers glue to help hold your pieces together should do the trick - item B8234 Glas Tac Firing Glue is a popular solution.


Wednesday, June 25, 2014
3 Posts

I am new to glass fusing and hae been trying out different pieces of glass to make pendants. Using the ripple glass I am having an issue. What's happening is the ripple glass seems to be slipping out fromthe clear glass on top -- most of it covers well but the sides or top seem to pop out of the clear glass even though they are the same size or even sometimes a bit larger. Any tips on this? Does the thickness of the clear glass matter? Kate