Zahur will decant potions for free. Players can either talk with her or use her right-click Combine option. She will decant all the potions in the player's inventory, noted or unnoted, and the player may choose what dose potions.
Upon completion of the hard Desert Achievement Diary, or when wearing the Herblore cape, Zahur will make unfinished potions for you for 200 coins per potion. You can take noted clean herbs and vials of water and she will give you noted unfinished potions in return for 200 coins per potion. Right clicking her, after the Diary completion, will make the option to "Make unfinished potion(s)" appear, it will combine all the herbs and vials given that you have enough gp in the inventory. Going through the dialog with her does not give an option to combine.