How to make ice crystal clear

I suppose you are asking about the cause of whitish color of ice.

Normal (commonly available) water is a mix of air molecules and other impurities. When we freeze this water, the water free of minerals and other impurities freezes first, and as a result, entrapped air and minerals are moved out of the freezing ice toward the unfrozen center.

So, the trapped air becomes dense and frozen water with air bubbles looks like cloudy or white in color as you mentioned.

You may distil or do a reverse osmosis to remove impurities from normal water, then boil this water to 100 degrees and wait until all their bubbles are removed. Then let the water cool down to room temperature. Then freeze it. You will get crystal clear ice cubes.