Polaroi Type 55 film is a black and white peel-apart Polaroid film that yields both a positive print and a negative image (which can be used in an enlarger). Though box-rated at 50 ISO, the positive and negative parts of the film are effectively rated at 50 and 35 , respectively. There are some photographers who rate the negative at 32 ISO. Polaroid rates the negative at 25 ISO. When processed and peeled apart, the positive needs a protective coating, included in the box of film, to keep it from fading and the negative needs to be cleared in a hypo-removing solution (Kodak's Hypo-Clear works). Polaroid recommends an 18% Sodium-Sulfite solution. Some photographers prefer to put the negative in a hardening fixer, though not all feel it necessary. The reason for this is that Type 55 negatives are very thin compared to other 4x5" negatives, and the emulsion is extremely soft.