You were both being incredibly unprofessional, IMO. You’re allowed to leave a class unsupervised? You couldn’t call down and ask about a can opener? Send a student to ask about a can opener? If it isn’t your equipment, permission needed. End of story. If you can’t get the last minute thing you need, that shows poor planning on your part and not an emergency on theirs. Adapt for the missing thing and come back to it later. You could have had the students move o. To something else and develop their film later. She shouldn’t have reprimanded you in front of your class, it’s happened to me before so I understand how awful it feels, but you were both in the wrong. I teach art so I heave people trying to take equipment or materials all the time and it gets very frustrating.