Ruby of the War Mage

Etched with eldritch runes, this 1-inch-diameter ruby allows you to use a Simple or Martial weapon as a Spellcasting Focus for your spells. For this property to work, you must attach the ruby to the weapon by pressing the ruby against it for at least 10 minutes. Thereafter, the ruby can't be removed unless you detach it as a Magic action, the weapon is destroyed, or your Attunement to the ruby ends.