Here is a guide on how to unlock the ability to buy infinite Smithing Stones +1, +2, +3, +4 in ELDEN RING.
How to get +1 and +2
… In Liurnia of the Lakes, there is a cave off to the North East Side. Location below, Raya Lucaria Crystal Caves.
Fighting your way to the end and beating the boss rewards you with a smithing bell bearing to give to the Twin Maiden Husks. This unlocks infinite smithing stone (1) and (2) at her shop.
How to get +3 and +4
To start hit the tunnel entrance to reveal a path going forward. Head forward past the first enemy and take your first right along the path blocked by some barrels, crates, and a wheelbarrow. Inside the room here there is a chest. Open the chest to get the Smithing-Stone Miner’s Bell Bearing.
Take the Smithing-Stone Miner’s Bell Bearing and head to the Roundtable Hold. Go to the Twin Maiden Husks and offer the Smithing-Stone Miner’s Bell Bearing to them. Doing this unlocks the Smithing Stones 3 & 4 for purchase from them. The prices are as follows:
Smithing Stone  – 2400.
Smithing Stone  – 3600.
These are the first set of major materials you can unlock from the twins. Once unlocked the sisters sell an infinite amount. The next few sets follow the same system. Find a bell, bring it to them, unlock the materials.
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