Hi Sakari. The pictures are really very funny, I wish I could recreate the same effect every time I wanted to...(posted 8236 days ago)Have you checked the surface of the emulsion ? Is it rough ? If the problem is created by emulsion swelling it is most probable you shall be able to feel that on the the emulsion. Look at the film emulsion by letting the light reflect on it. You should be able to see some kind of texture, different than the one on a normal emulsion. If there is no trace of all that, start asking yourself whether your student has not set up a nice (and clever) prank for his professors, by double exposing his negatives (one normal exposure of a subject and one of the bubbles in his bathtub)...