This page discusses sealing metal through borosilicate/lab glass: other chemistries behave quite differently. When making vacuum tubes, glass blowing is actually the easy part: premade tube stock of almost any size is easly avalable. Heating the end of such a tube softens the glasss and allows surface tension to close it off. I used a rotary vane pump to remove all the air from the tube and heated the middle, which the atmosphere crushed to create a sealed-off ampule. Because glass is practically impermable, it will retain that vacuum for a very long time, which can be shown by bringing it close to high-voltage AC (like a tesla coil): This glow is due to residual air being ionized, but the fuzzy apearance indicates that the vacuum is good enough to work in a triode or similar device. For those, the capacitive coupling trick won't work: I'll need to make electrodes that pass through the glass without letting air in. Copper's red oxide bonds very well to glass. In fact, the bond is…
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