73｜Glass Manufacturing Methods, Forming Methods, and Processing Methods 11

Hello everyone 🎵 I was on a business trip abroad for about a month, so I took a break from this topic. Starting this week, I'd like to resume our discussion, continuing from the glass manufacturing process.

The glass manufacturing process consists of: ① raw material blending, ② melting, ③ forming, ④ annealing, ⑤ finishing/inspection, and ⑥ packing/shipping. We've discussed ① and ②, and last time, we talked about free-blowing for ③ forming.

In free-blowing, molten glass is gathered onto the end of an iron pipe called a blowpipe, and while rotating the blowpipe in the air, the glass is shaped using tools like shears and pincers before being blown.

Controlling the blowing of the glass is difficult, and it requires advanced skill to blow it before it cools and solidifies. It is mainly used for forming items such as vases.

Today, let's talk about mold-blowing, which is used to produce many glasses among handmade glass products. Mold-blowing is a method of forming glass by creating a metal mold for the desired glass and blowing the glass gathered on a blowpipe into that mold. Compared to free-blowing, the forming is more stable, and a larger quantity can be produced. Glasses used in our daily lives, such as cups and wine glasses, are almost all manufactured by mold-blowing.

The process of mold-blowing (also called blow molding because air is blown into it for forming) begins with the raw materials being completely melted at 1400 degrees Celsius. This is then cooled to about 1200 degrees Celsius, which is an ideal temperature for gathering and forming the glass. A small amount of molten glass is gathered onto the blowpipe from the opening of the "Nekotsubo" (cat pot, a tool for gathering glass). This is then brought to a workbench, shaped with a ball-shaped tool called an "Tetsurin" (iron ring), and then air is blown into it. This is called "Shitama" (under-ball), the first layer of glass. After cooling this, another layer of glass is gathered from the furnace pot to create the second layer. While the glass is soft, it is shaped, and air is carefully blown from the blowpipe into the mold, causing it to expand.

In the past, the shape of the glass gathered from the "Nekotsubo" for the second layer from the "Shitama" was formed by hand, rotating the molten glass with wet newspaper. However, it seems the quality of newspaper has changed, and many factories now use carbon-based non-combustible fabric.

The thickness and texture of the glass can vary depending on the amount of glass the craftsman gathers, how they blow into it, the force they apply, the angle, and even the temperature and humidity of the factory where it is being formed. Craftsmen carefully and painstakingly blow and form each piece, striving to achieve the same size, thickness, and shape.