Glass Compatibility

What is glass compatibility and how is it important in your glass fusing process?

Let's take a look at what it is and how you can tell if your glass is compatible.

There are a multitude of glass manufacturers, and different ways of making glass.

Since you want to put different pieces of glass together in your projects, you will need to be sure that they are compatible.

Every piece of glass in your project needs to have the same COE or Coefficient of Expansion.

Different types of glass expand and contract at various temperatures.

This various temperature change is known as the COE or the Coefficient of Expansion.

Here is what a sticker on a piece of Bullseye glass looks like.

It indicates that the glass has been tested and is compatible with other Bullseye glass.

Glass Compatibility


If you don’t use the same Glass Compatibility, the stress will cause it to crack or break.

Since different COEs of glass expand and contract at different temperatures, they can not be fused in the same project.

So, the first decision you need to make is which COE of glass you want to use in your glass fusing projects.

The lower the COE, the harder the glass and a higher temperature is needed for it to begin melting.

Decide which COE of glass you are going to use, and stick with it in all your glass fusing projects.

There is a lot of glass that is used for doing stained glass, and it is not tested for COE.

, be sure your glass is designated as fusible glass and has the specified COE.

You can not tell the difference by look, so if you do purchase different COE glass, be sure to keep them separately in your studio.

Not sure of the COE…there are only a couple of ways to know if all of your glass is compatible.

  • Use glass that has been marked "Tested Compatible" by the manufacturer.

  • You can perform a compatibility testing on your own.

    Type of Glass and COE

  • Window (float) glass - 83 to 87 approximately – not tested compatible
  • Bullseye – 90 COE – tested compatible
  • Spectrum System 96 – 96 COE - tested compatible
  • Morretti – 104 COE – can vary, should do self test for compatibility

    Glass Compatibility is important for your pieces to fuse together.

    Again, two glasses with considerably different COEs are not compatible.

    Consequently, they should not be fused together.






    Return from this page to one of the following pages:

    Technical Terms

    Fusing and Slumping

    Glass Compatibility to Glass Fusing Made Easy

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