Manual blowing mainly uses a hollow iron pipe (or stainless steel pipe), one end for dipping glass liquid, the other end for manual blowing. The tube length is about 1.5-1.7 m and the central aperture is 0.5-1.5 cm. Different specifications of blowing tubes can be selected according to the size of the products.
Hand blowing mainly depends on skilled wood and my own operating experience. The operation method seems simple, but it is not easy to blow out the products that meet the requirements, especially the complicated art decorations.
The glass materials manually blown are mostly melted in crucibles (and also in small tank kiln towels). The change of forming temperature is complex. At the beginning, the forming temperature is higher, the viscosity of molten glass is smaller, the operation duration can be slightly longer, the uniformity time of glass in iron bowl can be slightly longer, and the small bubbles can also be slightly cooled. With the gradual decrease of glass in crucible and the prolongation of cooling time, the operation rhythm of the whole blowing moulding must be gradually accelerated.
Main skills of hand blowing:
(1) Homogeneous material should be uniform. The uniform distribution of hot glass in each part mainly depends on whether the rotating speed of the blown iron pipe is proper or not, and if the rotating speed is too fast or too slow, the local thickness of the product will be uneven.
(2) The blowing time and the blowing volume should be just right. Overblowing will make the product too thin and too large in size. On the contrary, it will make the end too thick and too small in size. Therefore, good luck and proper blowing force are the key to ensure the size of products.
(3) The weight of pick-up should be basically the same each time, because this forming method mainly relies on hand feeling and experience. The viscosities of liquid glass at the top of crucible are different from those near the bottom of crucible, especially when picking up materials.
Hand-blown moulding has high labor intensity and difficulty, but it can survive for thousands of years mainly because of its flexibility and artistry. So far, it is still an important moulding method in glass industry.