A trait of the Isa Rune is brittleness. It solidifies like water to ice. This hardening is usually temporary and can be fragile. Brittleness is a problem that contributes to the temporary nature of Isa hardening. It is not limited to ice. Metals like iron can be brittle and fragment easily. To counter brittleness, the process of tempering uses heat and cold. It imparts enough flexibility and softness to keep the metal from shattering. To the coldness of Isa, it’s reciprocal – heat – must be applied. Of course, improper tempering can go the other way and make the iron too soft and bendy.