Refining is exclusively reserved for Weapons.
You need to mine for Black Iron Ore and obtain various accessories, and hand it to a blacksmith.
The Blacksmith will take your weapon and the materials you want to use, you leave your weapon with the Blacksmith.
Once you get your weapon back, you have 1 nerve wracking swing to make, to see if your weapon gets an upgrade, or shatters into a thousand pieces (oh yeah, your weapon can break!)
Although there will always be some luck involved in refining learning the best Ore purities and accessories to use for each weapon is key to get the highest luck possible for the weapon to get it to upgrade!