Thank you for your comment ! The descriptions are not straightforward to encourage deduction and trial & errors, but indeed the feedbacks for the success or failure of the potion are not noticeable enough : the SFX is not ne same, and there is a text displayed at the top indicating it, but too small and too far away from what is looked at on the screen, which is mainly around the book and middle of the screen. For the fire, you can click on it to reset the current bowl and ingredients, not drag it into the fire, but indeed that's not crystal clear either.
Thank you for playing :D