I have been blowing glass on copper tubing for a while. I think 6 years or so? I know it works from doing it but I’ve never really understood why it works.
I create my skeletons by adding bits of glass to the copper tubing, always trying to see what I can come up with. I have moments of failure, pushing the boundaries a bit too hard, and I’m not always sure why they fail.
So for this post, I decided to look into why it works! And in researching this I realized why I never look into it! It can get complicated…
Coefficient of Thermal Expansion
When you are attaching things to glass while it’s hot you always come back to the coefficient of expansion (or COE). This is how much your glass shrinks and expands while being heated or cooled. Different glasses have different COE’s
and same with different metals
To keep glass from cracking you want these numbers to be the same.
You may have noticed that copper and glass don’t match…
So why does it work?
So for soft glass, which is what I use for these large skeletons, is all about oxidation. To be honest, I still don’t really understand oxidation...
Metal oxidation takes place when an ionic chemical reaction occurs on a metal's surface while oxygen is present. (so says the internet)
When I heat up the copper pipe in a torch flame a layer of oxidation forms on the tubing. When I encase that in glass it creates a barrier between the copper and glass. I guess that barrier is just enough wiggle room to help save the glass while it’s cooling.
It also matters that I use copper tubing instead of solid thick copper. It needs to be thinner to “get away” with attaching them.
It’s pretty cool!
And this is only for soft glass. I am currently working on smaller skeletons where I am using borosilicate glass, which makes it totally different!
In fact there are a bunch of different ways to attach metal to borosilicate for scientific glass blowing purposes. I will make another post about that process when I learn more!
I hope you’ve enjoyed learning about copper and glass with me.
What did you think?
Would you like to learn more about my process of actually making the skeletons? Did I get something wrong? Please let me know! I am no way an expert and love any new knowledge you can bring!
-Sarah