What is the primary condition for clear ice formation?

The primary condition for clear ice formation is the presence of supercooled large water drops. When water droplets are in a supercooled state, they remain liquid even at temperatures below freezing. This can lead to the formation of clear ice rather than clouded or opaque ice because the water can freeze in a more uniform manner without the presence of impurities or air bubbles that typically scatter light and create a clouded appearance.

In contrast, when water freezes rapidly or in small droplets, it can trap air and impurities, resulting in a frosty or opaque ice. Thus, the ability of large water droplets to remain in liquid form while being below freezing allows them to freeze more slowly and uniformly, which is essential for producing clear ice. Other conditions, like temperature or humidity, may influence ice formation but are not as directly relevant to achieving the clarity that supercooled water droplets provide.