(1) The homogeneous material should be uniform. The uniform distribution of hot glass in each part mainly depends on whether the rotation speed of the blown iron pipe is appropriate. If the rotation speed is too fast or too slow, the local thickness of the product will be uneven;

(2) The blowing time and blowing volume should be just right, too much blowing will make the end of the product too thin and the size is too large; otherwise, the end will be too thick and the size is too small. Therefore, free luck and proper blowing force are the key to ensure the size of the product.

(3) The weight of the material should be basically the same every time, because this molding method mainly depends on the feel and experience. The viscosity of the glass liquid in the upper part of the crucible is different from that near the bottom of the crucible, so special attention should be paid when picking materials.

Hand-blown molding is labor-intensive and difficult, but it has survived for thousands of years mainly because of its high flexibility and high artistry. So far, it is still an important molding method in the glass industry.