User Manual - Reagents Guide

Every enchantment recipe and formula will require exact quantities of reagents. Because that's not something Dragon age allows by default, you will have to follow those steps in order to split your reagents supplies into precise stacks.

Splitting stacks only works when the party is at the Warden Camp.

Splitting Reagents

Before anything, it's important to realise that only stacks of reagents prepared for the Enchantment process can be splitted. This includes Essences, Crystals and Imbued reagents, but not the original Dragon Age reagents such as Frostrocks. As for the reagents having an activable effect, they remain usable as usual when the party isn't at the Warden Camp. Which means using an Imbued Deep Mushroom in battle will have the same effect as using the original quickitem; you won't be splitting stacks when in dire need for an extra stamina boost, rest assured !

So, how to split a reagents stack ? You'll see it's fairly easy...
While your party is at the Warden, select one of these stacks in your inventory. Here, let's use greenstones :
Screen capture Summon the radial menu by right-clicking the stack, and choose "Use" :
Screen capture Then close your inventory. You'll see a popup window asking you to precise how much reagent you want to keep in your inventory, as the rest will be automatically send to your enchantment storage chest.
Why ? Because otherwise, the Dragon Age engine would automatically put the two stacks back together, which would kinda defeat the purpose of doing all this...
Screen capture For example, if your recipe or formula requires three of those reagents, simply type 3 in the popup field, and confirm. Your stack will be splitted, the rest send to the safety of your chest, and you'll see a message confirming you all is well :
Screen capture That's it, you're done.