The second third of the art of the glass-blower consists in being able to move both hands about, rotating a tube with each thumb and finger, and keeping the distance between the hands, and also the speed of rotation, constant. Nothing but long practice can give this facility, but it is essential that it be acquired to some extent, or no progress can be made. Some people acquire a moderate proficiency very quickly, others, of whom the writer is one, only become reasonably proficient by months, or even years, of practice.
Supposing that the tube is now ready to be drawn down, the operator will remove it from the flame, and will gently pull the ends apart, interrupting his turning as little as possible. If the tube be pulled too hard, or if the area heated be too small (about three-eighths of an inch in length in the case given would be proper), it will be found that the ends of the two portions of the tube will be nearly closed at a very sharp angle (nearly a right angle to the length of the tube), that the ends will be thin, and that a long length of very fine tube will be produced. To heat a short length of tube and pull hard and suddenly is the proper way to make a very fine capillary tube, but, in general, this is what we want to avoid.
If the operation be successfully performed, the drawn-down tube will have the appearance exhibited, which is suitable either for subsequently closing or handling by means of the drawn-down portion. The straightness of the point can be obtained by a little practice in "feeling" the glass when the tube is rotated as it cools just before it loses its viscous condition.
When the operation is carried out properly the shoulder of the "draw" should be perfectly symmetrical and of even thickness, and its axis regarded as that of a cone should lie in the axis of the tube produced. The operation should be repeated till the student finds that he can produce this result with certainty, and he should not be discouraged if this takes several days, or even weeks. Of course, it is probable that within the first hour he will succeed in making a tolerable job, but it is his business to learn never to make anything else.
Fig. 9.
Fig.
10. — Diagram of a folded end.