Red Ice

Red Ice is an object in.

Characteristics
Red Ice is a type of ice found in Link's adulthood in Zora's Domain, the Ice Cavern, and Ganon's Castle.

When Link returns to Zora's Domain, he finds King Zora frozen in Red Ice as a product of the freezing of Zora's Domain. He also finds the entrance to the Zora Shop blocked by the ice. While venturing in the Ice Cavern, Link finds Blue Fire, which can be scooped inside an empty Bottle and used to melt the Red Ice. Blue Fire can be used inside the cavern to gain access to Ruppes, Treasure Chests, and a Piece of Heart. Link can also take some Blue Fire to free King Zora, which will then reward him with the Zora Tunic. Link finds one last time some Red Ice inside Ganon's Castle water barrier area.

Theory
Unlike regular ice, Red Ice does not freeze Link when touched, suggesting that the ice is in fact "hot." This would appear to be supported by the fact that the ice can only be "melted" by the "cold flame" of Blue Fire.

Trivia

 * Red Ice may be based off of the crystallization of supersaturated solutions, also known as "hot ice."