When the stopper has been ground into its place, melt off the tail at F. The flame must be applied very cautiously, as glass which has been ground is particularly apt to crack on heating. To avoid all risk of this, the tail may simply be cut off, and its edges filed smooth with a file moistened freely with camphorated turpentine.
The stoppers of bottles are not made exactly in the manner described above, though, on occasion, a new stopper may be made for a bottle by following those directions. Ill-fitting stoppers, which are very common, can be very easily re-ground with emery and camphorated turpentine.
[6] Remember that when the lead glass is heated to the proper temperature it will present an appearance which may be described as a greenish phosphorescence. At higher temperatures it assumes an orange-red appearance. If it loses its transparency and assumes a dull appearance, it must be moved further into the oxidising parts of the flame.
[7] Some glass-blowers at once work on the glass as next described, without this preliminary treatment. I find that some glass, usually soda glass, will not always bear the necessary movements without breaking unless first heated all round.
[8] If such an opening be observed, it may usually be closed by touching its edges with a fused point of glass at the end of a drawn out tube.
[9] This can be obtained from Messrs. Powells, Whitefriars Glassworks.
[10] Mr. Gimmingham recommends giving stoppers a final polish with rotten-stone (Proceedings of the Royal Society, p. 396, 1876).