It means that once you reach grift 30, you should absolutely augment your weapon if it is ancient, and then every 5-10 grifts re-augment it. However, it doesn’t mean that you should use a 30, 40, or 50 ranks gem.

If you want to augment armor, the legendary gem you use must be at least rank 50.If you’re augmenting jewelry, the legendary gem you use must be at least rank 40.

If you want to augment a weapon, the legendary gem you use must rank 30.You should be taking your off stat gems (as in, if you are a Demon Hunter and don’t use Topaz) and using Convert Gem to get them to your primary stat type. +210 Dexterity (Caldesann’s Despair Rank 42) These are the correlations for gems to stats: So, for example, let’s say you used a level 42 legendary gem with an emerald. The result is a unique blue stat name on your item called “Caldesann’s Despair” (the name of the cube recipe for augmenting), as well as the rank and bonus to the stat. As the accepted answer states, you get +5 for every rank of the gem. They are one of the keys to progressing into the upper greater rifts. These augments are extremely important for endgame content.

If you augment a second time, it just overwrites the first augment. You aren’t able to augment twice to double the effect, though. So, a rank 50 legendary gem will give you an additional 250 to your primary stat (chosen by standard gem type). The legendary gems are the critical component in this recipe you receive +5 points to an attribute chosen by Flawless Royal gem (Amethyst for Vit, Ruby for Strength, Emerald for Dex, Topaz for Int, regardless of item type) for every rank of your legendary gem. How does augment ancient items work? So basically, what this recipe does is make your current ancient item better.

Diablo 3 augment ancient item gem