Thus arsenic, antimony, bismuth, tin or zinc render the metal brittle, so that it fractures under a die or rolling mill; copper, on the other hand, increases its hardness, makes it tougher and more readily fusible.
He couldn't help thinking his mama had been a little tougher when she found out about the Immortals.
In metal bridges wrought iron has been replaced by mild steel - a stronger, tougher and better material.
They are of a tougher fibre than the Aroras; sturdy and self-reliant, slow to speak but quick to strike.
The best poles are obtained in Norway from small, slender, drawn-up trees, growing under the shade of the larger ones in the thick woods, these being freer from knots, and tougher from their slower growth.