The opposite of brittleness is ductility. Excessive hardness may induce brittleness, which should be avoided. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. Ice quality is judged by smoothness, friction, hardness, and brittleness. It is distinguishable from native gold by its hardness, brittleness and crystal form. Zinc oxide is added to reduce brittleness and improve plasticity. Software brittleness is the opposite of robustness. Additional time above liquidus may cause excessive intermetallic growth, which can lead to joint brittleness. This revealed sign of brittleness with no permanent plastic deformation before it broke. In general, due to its brittleness temperature gradients in glass might cause cracks. Environmental cold can lead to the contraction of the fixed rail causing brittleness and cracks. Regardless, the maximum impact energy of high-strength steels is still low due to their brittleness. These chemical reactions physically weaken the paper, causing brittleness. It lacks the brittleness of concrete and consequently does not need expansion joints. This is because the brittleness of glass does not allow for uneven thermal expansion.