Mixing Bottle Glass for Fusing

The most frequent question that I get is “Can I fuse different kinds of bottles together? I saw someone else doing it and it seems to work.” followed by “My fused bottle projects are breaking in the kiln or later, how do I fix that?” See the pattern? So, I thought I’d show you what is happening IN the glass when you fuse different bottles together.

I started with clear bottle glass, I fused the glass from one bottle with itself as a control. (I also did a kiln carving pattern with it because I like to multitask.)

heart kiln carving pattern
flaming heart kiln carving pattern finished project

Then I assemble two mixed bottle glass fusing projects. Each one uses clear glass, two pieces from the same bottle, and different colors of bottle glass. The first one has a ring from a brown bottle around the bottom of a green bottle and I sandwiched it between two sheets of clear (the top isn’t on yet in this photo).

fusing mixed bottle glass
Fusing clear, brown and green glass

The second has a clear base, a lime green ring with a cobalt ring inside of that, and a lime bottle bottom inside of the cobalt ring, with the other clear piece on top.

fusing mixed bottle glass
Fusing clear, lime and cobalt glass

Then I fused them using my handy full fuse schedule.

fused mixed bottle glass
Fused clear, green and cobalt glass
fused mixed bottle glass
Fused clear, brown and green glass

And look at that, they SEEMED to work, now let’s take a look inside. Using a polarized filter, I’m going to check for stress in the glass. Internal stress is a strong indicator of incompatibility or poor annealing. Either way, your project is headed for cracking eventually. Let’s start with our control project. If it shows internal stress, then we have an annealing problem. We know the glass is compatible, because it came from one bottle and glass is always self compatible.

fused bottle glass stress test
Stress test for control fused project

Stess shows up as flares of yellow or white in the glass. I think it’s safe to say there is little or no stress in our control project. Sweet! Now, let’s look at our mixed fused glass projects.

fused mixed bottle glass stress test
Fused clear, green and brown stress test
mixed fused glass stress test
Fused clear, green and cobalt stress test

This is problematic. The flares in the glass are showing substantial amounts of internal stress. The solid yellow circle under the lime green ring is particularly troubling, as are the flares around the brown ring.

fused mixed bottle glass stress test
Fused mixed bottle glass stress test

So, my conclusion is, although it SEEMS to work, and the results are pretty, I would be uncomfortable selling something that I knew had problems and would likely break later. There are so many, many other techniques and things you can do with fused bottle glass that I would not recommend mixing bottle glass for fusing without testing for stress and compatibility.

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