Laboratory Manual of Glass-Blowing

by Francis C. Frary

Fig. 3.—Flanging a tube with flanging tool.

Fig. 4.—Flanging a tube with carbon rod or wire.

Some glass-blowers use a small carbon rod, about ³⁄16 inch in diameter, as a flanging tool for tubes larger than about ³⁄8 inch diameter, and a small iron wire or similar piece of metal for smaller tubes. In this case the tube is heated as above described, and the rod or wire inserted in the end at an angle and pressed against the softened part, as indicated in Fig. 4, while the tube is rotated about its axis. For large heavy tubes a larger carbon would be used.

Rotation of the Tube.—This is the fundamental manipulation in glass-blowing, and upon it more than all else depends the uniformity and finish of the work, and often the possibility of accomplishing the work at all. Directions for it will be given on the assumption that the reader is right-handed; if otherwise, the position of the hands is of course reversed. The object of rotation is to insure even heating of the whole circumference of the tube at the point of attack, to equalize the effect of gravity on the hot glass and prevent it from falling out of shape when soft, and to keep the parts of the tube on each side of the heated portion in the same straight line.

In rotating the tube, both hands must be used, so that the two ends may revolve at the same rate and the glass in the hot part not be twisted. The rotation is performed by the thumb and first finger of each hand, the other fingers serving to support the tube. As it is almost always necessary to follow rotating and heating a tube by blowing it, the hands should be so placed that it will be easy to bring the right-hand end up to the mouth without shifting the hold on the glass. For this reason the left hand grasps the glass with the palm down, and the right hand with the palm turned toward the left. If there is any choice, the longer and heavier part of the tube is usually given to the left hand, and it is planned to blow into the shorter end. This is because it is easier to support the tube with the hand which has the palm down. This support is accomplished by bending the hand at the wrist so that it points slightly downward, and then curling the second, third and little fingers in under the tube, which is held between them and the palm. This support should be loose enough so that the thumb and first finger can easily cause the tube to rotate regularly on its axis, but firm enough to carry all the weight of the tube, leaving the thumb and first finger nothing to do but rotate it. The hand must be so turned, and the other fingers so bent, that the thumb and first finger stretch out nearly to their full length to grasp the tube comfortably.

The right hand is held with the palm toward the left, the fingers except the first slightly bent, and the tube held between the first finger and the thumb while it rests on the second finger and that portion of the hand between the base of the first finger and the thumb. Rotation of the tube is accomplished by rolling it between the thumbs and first fingers: the rotation being continued in the same direction regularly, and not reversed. It is better to roll slowly and evenly, with a series of light touches, each of which moves the tube a little, than to attempt to turn the tube a half a revolution or so with each motion of the hands. The hands must be held steady, and the tube must be under good control at all times, so that both ends may be rotated at the same angular velocity, even though they may be of different diameters, and the tube be neither drawn apart nor pushed together unless such a motion is expressly desired, as it sometimes is. The hot part of the glass must be constantly watched to see that it is uniformly rotated and not twisted, nor pulled out or pushed together more than is desired. Care must also be taken to keep the parts of the tube in the same straight line, or as near it as possible, during the heating and all other manipulations.

When flanging a tube, it is held and rotated with the left hand as above described, while the right hand holds the flanging tool.

When part of the end of a tube must be heated, as in Exercise 6, and rotation must be very carefully performed and continued during the blowing, both hands are used. The right hand is held as above described, and the left hand close to it and either as above described or else with the palm toward the right, grasping the tube in the same way as the right hand does. This puts both hands in a position where the tube may be blown and rotated uniformly while its axis is kept horizontal.