Slumping a Glass Tray on Fibreboard


In a previous post I talked about making a fibreboard mold for slumping a fused glass tray. The post was all about the process I followed making the mold.

In this post I will cover fusing the rectangular piece for the tray and then slumping it to form the tray.

Fusing the Tray

Fused Glass Tray - Before Firing
Fused Glass Tray – Before Firing

All glass used for the tray is Bullseye COE 90. All glass came from our offcut bins so I am sorry but I can’t supply the product code for it all.

The tray was assembled from a base layer of clear glass (1101). This was an offcut and it didn’t quite fit the width of the mold. It was long enough but a little short on the long sides. These narrow sides turned out to be a mistake I will cover a little later.

On top of the base I used a green (yes it looks black, but it is dark green) strip at each end and a thin strip down the side. Again, dictated by the sizes of the offcuts available.

Between the strips I laid in a piece of yellow. Decoration on top consisted of stringers and a few clear dots.

The design wasn’t as important as the test for the mold.

This was all fired to a full fuse on Bullseye Thinfire paper. The firing schedule is below.

Fused Glass Tray - After Firi
Fused Glass Tray – After Firiing

The end result can be seen in this photo.

At this stage I was very happy with the result, though I did notice the green had not fused around the sides. I believe this is because I didn’t cut the green larger enough so it overlapped the base properly. Something for you to be aware of.

The stringers fused in nicely and retained their crisp definition. The clear dots added the nice subtle variation to the yellow. The yellow did change colour a little, tending to be more orange in colour.

The Slumping

Oops. forgot to take a photo of the tray on the mold prior to slumping, but I am sure you can imagine what it looked like.

Fused Glass Tray - After Slumping
Fused Glass Tray – After Slumping

As you can see in the photo the result is not quite right. The sides of the tray have pulled in substantially.

The cause was obvious. If you look you can see that the ends of the tray are fine. However, on the sides the tray only sat on the mold about 1 cm. It appears that as the glass slumped into the mold it pulled the sides in. I do believe that if the sides were wider there would have been enough weight and resistance on the mold to stop the sides pulling.

Other than that, the mold worked perfectly. The tray separated from the mold very easily and very cleanly.


  • Don’t forget to take photos, before and after.
  • If you have a clear base be sure to cut your top pieces slightly larger so the colour fuses around the edge.
  • With long sided flat molds, size your finished piece so it sits flat on the side enough to provide sufficient glass volume to keep it stable during slumping.

Firing Schedules

Full Fuse – 2 Layers 3mm Bullseye COE 90, plus decoration

Segment Rate (C/hr) Target (C) Hold (mns)
1. Strain Release 270 538 10
2. Process FULL 800 20
Crash Cool Open Door 560 0
3. Anneal FULL 516 60
4. Cool 180 371 5

Slump Firing

Segment Rate (C/hr) Target (C) Hold (mns)
1. Process 167 638 10
3. Anneal FULL 482 60
4. Cool 55 371 0

2 thoughts on “Slumping a Glass Tray on Fibreboard”

  1. Barbara Anne Jamison

    Thanks for your great explanations.

    When I use a fibreboard mold, the areas touching the fibreboard are always very rough. What am I doing wrong?


Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top