Why bottle glass doesn't have a standard CoE.
Wouldn't it be great if all bottle glass and float glass had the same CoE and you could just mix all that stuff up and not worry about it? There are good reasons why it doesn't always work.
Short answer:
Bottle glass formulations vary by factory and by cost of materials. Some of the materials in glass can vary enough to effect the thermal expansion properties. (Coefficient of Expansion in our world)
Art glass formulations are tightly controlled and extensively tested for compatibility (hence the cost). Your best bet is to
group bottles by factory to maximize possible compatibility.
Long and sciencey answer:
1. Bottle (and other factory glass) composition is variable. I found this awesome chart on
glassproperties.com
Soda-lime glass composition (containers, float glass e.g. for windows), mol%
| |
Typical container glass |
Typical float glass |
Approximate limits |
| SiO2 |
74.42 |
71.86 |
63-81 |
| Al2O3 |
0.75 |
0.08 |
0-2 |
| MgO |
0.30 |
5.64 |
0-6 |
| CaO |
11.27 |
9.23 |
7-14 |
| Li2O |
0.00 |
0.00 |
0-2 |
| Na2O |
12.9 |
13.13 |
9-15 |
| K2O |
0.19 |
0.02 |
0-1.5 |
| Fe2O3 |
0.01 |
0.04 |
0-0.6 |
| Cr2O3 |
0.00 |
0.00 |
0-0.2 |
| MnO2 |
0.00 |
0.00 |
0-0.2 |
| Co3O4 |
0.00 |
0.00 |
0-0.1 |
| TiO2 |
0.01 |
0.01 |
0-0.8 |
| SO3 |
0.16 |
0.00 |
0-0.2 |
| Se |
0.00 |
0.00 |
0-0.1 |
Compare the columns for typical container glass and typical float glass. See how they are different?
The thing you need to know is this:
"Both soda and potash exert such a dominating effect on the expansion of the glass that slight variations in the chemical composition, in some cases of even less than 1%, can cause significant variation in the thermal expansion." from
How Glass Changed the World, The History and Chemistry of Glass from Antiquity to the 13th Century. Seth C. Rasmussen, Spring Briefs in Molecular Science.
Now look at the Approximate Limits column showing further variations. (this is in mol%, which can be converted to weight% for the really dedicated chemistry types.)
For more science based glass information, I highly recommend:
Handbook of Glass Manufacture, Vol I and Vol II, as well as Modern Glass Practices.
Thanks for reading, and, as always, let me know if you have questions, I'm happy to help!
