Even though it is normal to place the wire between two layers of glass, it often moves from its original placing.
Using glue only keeps the wire in place while moving the piece(s) to the kiln. The glue will burn off at just under 500C, which is before the sticky point of glass, so it cannot hold the wire in place at the critical temperature – from about 700C. In fact, if you fire quickly the glue can “boil” and cause the wire to move.
There are a variety of methods to help keep the wire where you placed it. Some of them follow.
You can try weighting the wire down with small scraps of glass to keep the wire in place until the glass sticks to the wire. The scrap will often form a small bead that can be used in other projects. Sometimes though, the scrap sticks to the wire.
Another method is to place a small piece of 3mm fibre paper under the wire to support it during the firing. This will be enough to keep the wire from moving, and the scraps of fibre paper can be reused many times.
You could also bend the wire loop so that the end touches the shelf. The part in between the glass needs to be flat with the bend starting after the wire emerges from the glass. You can bend the wire straight after firing.
Flattening the wire by tapping the wire – placed on an anvil – with a hammer will reduce the possibilities of movement, and certainly any rolling possibilities. It will also have a greater area of contact with the glass.
You can also make a shallow groove in the glass where the wire is to go. This can be done with a Dremel type tool with a diamond bit, or on the small diameter bit on the top of a glass grinder.
Lay the glass in the groove and cap with the top piece.