The Rune of The Orb increases the capacity of the Blood Orb that is inside of the Altar by +2% additively per rune while it is inside of the Altar.
With some Netherite Scrap and some Intricate Hellforged Parts looted from the Demon Realm, you can double the power of your Rune of the Orb, increasing the orb's capacity by an additive +4% per rune.
If you change your mind, you can undo the recipe in the ARC.