The black iron ring was an uncommon reward from the Squeal of Fortune. It had 10 charges. It allowed players to summon Evryn, who would appear as a "helpful dwarf that is assisting you with some mining". Upon his arrival, Evryn would give the player 1 to 4 Dwarven black iron ore every 9–11 minutes; this consumed one charge. It was possible that two charges would be consumed, providing the player with 2 to 6 of the ore. After the black iron ring reached zero charges and the player continued to mine whilst wearing it, one more charge would be used and the ring would be destroyed. The ring also worked while mining at your clan citadel.
As of a recent update, it had an option to shatter the ring for immediate Mining or Smithing experience. This would also destroy the ring. The amount of experience given depended on your Smithing or Mining level. This option however would only grant you around 50% of the xp you would normally get. Your ring had to be unused to shatter it. Once it had already used one or more charges it could no longer be shattered.
On 15 October 2013, Jagex announced, "The rings will remain in-game for two weeks, after which they will disappear..."
Multiple black iron rings would not stack in bank even if they were all unused.
A glitch allowed for unlimited charges from a single ring during its appearance in Runescape. This was accomplished by removing or swapping the ring out into your inventory once Evryn appeared. You still received the ore from Evryn, but a charge would not be consumed. This bug was never patched.