The obsidian gloves are part of untradeable and degradable Obsidian armour set. They require 60 Defence to wear, and can be made by smithing one obsidian bar, requiring 80 Smithing. Obsidian bars are made by smelting obsidian shards, which in turn are dropped by monsters in the Fight Cauldron.
They provide a 5% reduction to damage from creatures and players in TzHaar City.
With an update on the 30th April 2013, the armour no longer triples damage taken by you when fighting in PvP or any other monster.
When used with the rest of the obsidian armour and either an melee, ranged or magic helmet, it will increase your accuracy by 10%, very similar to the Void Knight equipment.
The Obsidian gloves degrade after 4000 hits. Once they fully degrade they cannot be reused, and new gloves must be smithed.