Repurposing Glass – COE is critical

Repurposing Glass is not as easy as 1,2,3.

“I have these pieces that I don’t want. Can you do something with them?”

We get contacted several times a month about this. Here’s the scoop:

Every glass has its set of chemical and mechanical properties. If you don’t know what those are, you can’t work on a piece without some “experimentation.” One of the most important factors is the COE (coefficient of expansion) of the glass.

For glass pieces created under ambient conditions, stained glass and mosaic glass, knowing the COE is not essential because the material (the glass) is not being heated and cooled to different temperatures. For glass forms created using kiln forming or hot glass techniques, the COE is essential. You can sometimes get away with fusing or blowing glass with a 1 or 2 COE difference, but not always. If it is not compatible, it develops lines of stress along which it can fracture.

Here are some of the various COE’s for glass:

Type of GlassCommon NameCOE
Effetre (Moretti)lampworking glass104
Spruce Pine Batch for GlassBlowingBatch96
Spectrum, Uroborus Glass96
Bullseye Glass90
Standard Window Glass“Float Glass”84-87
Brown Beer Bottles83-90

The typical COE for most glass blowing studios is 96. The raw material for the glassblowing furnace comes in the form of cullet, which is silica sand that is superheated with other chemicals or batch. We currently use Spruce Pine Batch as our raw material. Furnace workers are typically called “soft glass” glassblowers.

The boro glassblowers are known as “hard glass” workers, and their pieces are made with glass that has a higher resistance to thermal shocking and breaking.

Manufactured glass that comes from different plants may result in products with varying COEs. For example, bottles made at one plant might have one COE, but the COE might be different at another plant of the same manufacturer.

So, if you want us to combine your glass shards with ours, we will try it. There will be a fee for the attempt, regardless of the outcome. We will do our best to be successful, but there are no guarantees. If it is successful and you want us to custom designs with your shards, we will estimate a price (again, it will be a payment due regardless of the outcome). There are no guarantees when you don’t know the COE.

Enriching lives through artistic self-expression.