We also figured out how to make direct glass-to-metal joints at some point. Widely used in mass-manufactured stuff, but I think you can also buy just a glass-to-metal transition or feedthrough by itself if you're doing custom glasswork.
There are a few people who make most of the copper to borosilicate glass joints in the world. It's really hard to do, and they're quite good at it. Don't try to make your own as a cost-saving measure!
A major challenge is matching thermal expansion coefficients. Copper expands quite a lot, and borosilicate barely moves at all, so they make a joint to a glass that moves less than copper, but more than boro, then they add a little bit of another glass, and so on until they've gradually transitioned from the copper to the borosilicate. Those well-made joints can be cooled to liquid helium temperature (4 K) without issue.
Yes, but you need to be able to bond glass to the alloy (note the color shift in that housekeeper's seal), and nickel alloys like kovar tend to have a really high magnetic permeability, limiting their application in experiments that need highly controlled magnetic fields.
