Yes after the aluminum plate is sensitized it would be placed in the holder collodion side down toward the darkslide. The glass would then be placed on top of that. Notice the little corner pieces at the corners of the insert. That is what the plates rest on. There is a spring clip in the center of the door that is hard to see( I'll take a better pic of it). When the door is closed it presses against the plates to hold them in place.