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20/08/19: I was informed by a reader that, thanks to the popularity of vaping and the extensive experimentation people seem to do with different heating elements, you can actually buy both Alloy 52 and Alloy 48 in wire form! It's sold as "NiFe52" and "NiFe48" wire. One online stockist is Zivipf.de - I've just ordered some Alloy 52 and will see how it works out.
One of the common alloys use for sealing to soda-lime glass is "Alloy 52". This is a nickel/iron alloy with 52% nickel, 48% iron. Getting hold of small quantities of this alloy is difficult, as most manufacturers want to sell you a large reel or draw wire to your own specific size. Fortunately, reed switches provide a nice, cheap source of short lengths of NiFe wire, pre-beaded with glass. There is an excellent description on Schott's site about the glasses and alloys used in reed switch manufacture.
The reed switches are RS part number 362-2518 and are around £0.40 each. Pretty much any size or style of reed switch can be used, and they are available very cheaply on EBay. The glass is first cracked in the middle and the loose glass broken away with pliers, leaving a rough bead of glass near the end where the wire was sealed to the glass. This is then fused in a small flame to provide a nice bead, ready for sealing to whatever other glass you might want to use. The photos below show the process.
 Intact reed switches |
 Broken in middle |
 Excess glass cracked away |
 Remaining glass fused to a bead |
 Summary of the procedure |
Although the wires are quite short on the inside of the reed switch, additional wire can be spot-welded on to increase the length. If you are attempting to seal glass to the bare wire, keep in mind that the wire was originally tin-plated and this should be removed with sandpaper before attempting a seal.
24/02/11: Here is a nice example of sealing one of the reed-switch wires into a glass tube. The tubing is 6mm OD and the joint was made on a glass lathe to keep the wire concentric with the tube as the glass melted.
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27/05/11: Here are a couple of interesting things I tried. First is extending the reed switch wires by welding on an additional length of 0.5mm stainless steel wire. For this, I used pulse TIG welding with my footswitch timer. The other pic is just of two reed switch wires with their glass beads fused together, to show it's possible.
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28/05/12: I made a device to butt-weld longer wires to the end of reed switch wires, making them more useful for feedthroughs.
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