The transparency of ice cubes has nothing to do with water. If the water is placed at low temperature, the outer layer will cool down first. Solidified. The inner layer is wrapped. When water solidifies, it expands. Naturally, many gaps and bubbles are wrapped up, making it obviously opaque.

If you are in the north, the ice lamps in winter are also very transparent, because they are ice sawn from the river, and the river water is frozen layer by layer from top to bottom. Of course, it will not cover cracks or bubbles. Something.

Pour a thin layer of water into the container, wait for it to solidify, pour another layer, and then freeze. Do this. The transparency will be better. The key is to let the water solidify and spread in one direction. Instead of surrounding it from all sides to the middle.