65｜Glass Manufacturing Methods, Forming Methods, and Processing Methods 3

Hello everyone 🎵

Since the end of June, Tokyo has been experiencing abnormally hot weather. While some areas like Shizuoka and Kiryu have seen temperatures exceeding 40 degrees Celsius, Tokyo has also had a continuous streak of intensely hot days above 35 degrees Celsius. With such heat even before the end of the rainy season, I'm concerned about even more intense heat after it clears. Please remember to stay hydrated and take regular breaks.

I started by discussing the raw materials for glass, which can be categorized into soda-lime glass, crystal glass, and borosilicate glass depending on the type of raw material used. Last time, I talked about soda-lime glass.

So, why is it called soda-lime glass? It's because soda ash is used as a raw material. The three basic raw materials for soda-lime glass are: ① silica sand, ② soda ash, and ③ limestone.

Now, crystal glass is made by adding metals such as lead or potassium to the raw materials of soda-lime glass. Originally, crystal glass invented in the Middle Ages contained lead. This lead, however, was not highly toxic lead, but rather a different compound called lead oxide, which is considered safe for the human body. ISO international standards and food sanitation laws clearly define the leaching standards for toxic lead, and all manufacturers are obligated to strictly adhere to them. However, the world trend is becoming stricter on lead, as seen in regulations like the RoHS Directive, which severely restricts the use of lead in electrical and electronic products. The prevailing trend is to avoid lead altogether. Therefore, the glass industry is also developing crystal and crystalline glass by adding other metals such as potassium and titanium instead of lead, and lead-free crystal (crystalline) glass is now the mainstream.

Crystal glass means glass that is as transparent as crystal. It has been branded as a luxury item due to its various characteristics compared to soda-lime glass.

1. Heavy feel - Because it contains metal in its raw materials, it feels heavier and more substantial when held compared to soda-lime glass. 2. High transparency and high refractive index - Due to the high molecular weight of metals, it sparkles and shines brilliantly. The refractive index is determined by crystal standards, so it is often used for Edo Kiriko and cut glass. The sparkling brilliance further enhances its luxurious feel, making it a favorite among customers.

3. When you flick the glass, a high-pitched metallic sound resonates. Compared to soda-lime glass, a ringing high-pitched sound can be heard when you flick crystal glass.

I recall my late father skillfully tapping the glass with his finger, producing that ringing sound, and proudly smiling as he said, "This is crystal glass."

Next time, I will talk about red crystal which uses lead, and crystal glass (crystalline) which does not use lead.