Gems go into your equipment's sockets and add effects to the hero wearing the piece. You keep and work on them in the Gem Chamber, inside the Armory.
Tiers and effects
There are six tiers, from I to VI, and a higher tier is worth more. Tier VI doesn't come from the Arcane Vault: it comes from fusing three tier V gems. Each effect's page shows its value per tier and its cap.
Effects fall into three domains:
| Domain | Socket | Effects |
|---|---|---|
| Offensive | Fury | Attack, Crit Chance, Crit Damage, Penetration, Lifesteal, Precision |
| Defensive | Bulwark | Defense, HP, Dodge, Block, Damage Reduction |
| Utility | Trail | March Speed |
Some gems carry more than one stat. In that case the gem's value is split between them, at a discount: on a two-stat gem, each stat is worth about 40% of what it would be on a single-stat gem; on a three-stat gem, about 21.7%. You gain flexibility, not extra power.
Sockets
The higher a piece's rarity, the more sockets it has; each equipment page shows how many. The socket's color depends on the slot:
- Fury (offensive): weapons and gloves.
- Bulwark (defensive): helm, chest, boots and belt.
- Trail (utility): cloak and mount.
- Prismatic (takes any gem): necklace and ring. On Epic and Legendary pieces, the last socket in other slots can also come out prismatic.
A gem only fits a socket of its own domain or a prismatic one. Multi-stat gems and keystone gems only fit prismatic sockets.
What the Forge unlocks
Your Forge level decides the highest tier the Arcane Vault can roll, which effects can come out (basic ones first, advanced ones later), whether two-stat gems can drop, and when cutting and adding an affix open up. The Forge page shows what each level unlocks.
Fusion
At the Forge Bench, three free gems of the same tier become one of the next tier. Fusion works from tier I to V — three V gems become one VI. If two of the three share an effect, that effect carries over; if all three differ, one is picked at random. Auto-fusion repeats this in a cascade up to the tier you choose, but stops at V: fusing into VI is always manual.
Only free gems go into fusion, manual or automatic. To fuse a gem that's socketed in a piece of gear, unsocket it first.
Cutting
Cutting spends Runic Dust, and the gem must be out of your equipment:
- Dissolve breaks a gem down into dust. Higher tiers give more dust, and the gem is gone for good.
- Cut swaps the effect of a single-stat gem for another one your Forge has already unlocked.
- Add affix gives a single-stat battle gem a second, random battle stat. Utility gems and low-tier gems don't accept it.
Dust costs show right on the screen.
Limits and diminishing returns
Each hero has a budget of active gems: 30 combat, 4 utility and 1 keystone. Socketing more doesn't break anything: the strongest ones stay active and the rest stay installed, with no effect.
Each effect also has a cap on the total from the hero's gems. Near it, each extra point is worth less, and past it you get nothing. Stacking a single effect stops paying off; spreading across effects usually does better.
Keystones
Keystones are unique effects that trigger at specific moments in a fight: First Blood, Bulwark Thorns, Bloodsucker, King's Breath and Final Judgment. Each one's page explains its trigger.
They work in army battles and, when the server enables them, in Guild War duels. Colossus duels ignore them. Two complete sets also grant a keystone, which competes for the same slot as gems (see Sets and relics).