| Several times I have (just for fun) been able to put glass beads on copper wire and achieve seals with the proper color associated with a copper-to-glass bond. But, I hear that copper wire isn't that good for use with soda-lime glass because of the mismatched COE. I have the following questions:
1) Failed Seal Appearance:
Since copper's COE is higher than that of soda-lime glass, the copper wire inside the glass should be trying to shrink away from the glass surface in a completed seal. Obviously thin annealed copper wire is able to just deform and accommodate that, but with thicker wires I hear this isn't the case. Would the red color disappear, or would there be some other indication of a failed seal?
2) Making More Reliable Seals:
The copper wire I use is thin, but I think I can do better. What if I smash the middle of the wire really thin (like molybdenum foil seals in quartz) and then make the seal? Would that be better / more reliable?
3) Pre-Beaded vs Pinched:
Most mass-produced pinch seals are made by just pinching the glass tubing over the Dumet wire. But, I feel like making the glass-to-metal bond in a more controlled and finely-tuneable setting would be better for at-home glassworking. Is there any reason not to put a bead on the wire first and then pinch that beaded wire into the glass stem for a completed seal?
4) Nickel-Iron Alloys For Borosilicate:
• There is Dumet for soft glass, Kovar for "hard glass" (COE 5), but what is the name of the alloy used for borosilicate? I doubt they just use tungsten, there has to be an alloy out there somewhere.
Thanks so much!
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