Dùng nước tinh khiết. Đun sôi nước hai lần Đổ nước vào khay đá hoặc khuôn và đậy kín bằng màng bọc thực phẩm để ngăn các hạt nhỏ rơi vào bề mặt đá. Cho khay đá vào tủ đông. Sau đó, lấy khay đá ra và nhẹ nhàng gỡ từng viên đá.

I'm interested in that, but I only have a few mins. Can you give me at most the first 500 characters of a detailed explanation in English about that?
This method looks to get as much of the air and mineral impurities out of the water as possible before freezing, start with already distilled water. Filtered bottled water will work, or any water purified by reverse osmosis. oil the water twice. Boiling removes air bubbles from the liquid, allowing the water molecules to stick together even harder in the freezer.  After boiling the first time, allow the water to cool. Then boil again. Keep the cooling water covered to prevent any dust from colle