How to Upgrade Gear with Titanite Shards, Chunks, and Slabs
The Titanite Ladder
Weapon and gear upgrades use a tiered material chain: Titanite Shard, Large Titanite Shard, Titanite Chunk, and Titanite Slab. Each tier is rarer than the last and is used for higher upgrade levels. Gather lower tiers first; they are the most common.
Smithing Transform
The upgrade itself is performed through a smithing_transform recipe. This means you combine your gear with the appropriate titanite item at a smithing table. The titanite item is consumed and the gear's upgrade level increases. Match the titanite tier to the upgrade level you are pursuing — early levels take Titanite Shard, later levels take Large Titanite Shard, then Titanite Chunk, and the final step takes a Titanite Slab.
Smelting Titanite
Some titanite items are produced by smelting. If you have raw material that smelts into a titanite item, use a furnace to convert it. Check your furnace recipes for the titanite output before assuming you must find every piece in the world.
Planning Your Upgrades
Decide which weapon you will commit to before spending a Titanite Slab, since slabs are the scarcest tier. Use Titanite Shard and Large Titanite Shard freely on gear you will keep, and save Titanite Chunk and Titanite Slab for your final weapon.