A new recipe to the cube was added with the 2.4 update, which is augmenting ancient items.
The recipe is pretty clear, but I saw people ruining their items by adding wrong stats (intelligence on demon hunter etc.). Is it related to the gems’ types?
For example, if I used Royal Emeralds, would I get dexterity (considering it is an armor piece)?
So basically what this recipe does is it makes your current ancient item better.
The legendary gems are the important 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. So, a rank 50 legendary gem will give you an additional 250 to your main stat (chosen by normal gem type). You aren’t able to augment twice to double the effect though, if you augment a second time it just overwrites the first augment.
The whole purpose of this is to just inch closer and closer to complete BiS (Best In Slot).
Hope this helped.