Value of photographs exceeds, oftentimes, the written record in historical research; photographs are deteriorating, especially those films produced on cellulose nitrate; early photographers produced negatives on plates sensitized by their own recipes and printed them on paper similarly sensitized, resulting in a variety of problems for the conservator; later factory-produced materials also presented a variety of problems (careful solvent-swabbing of a dirty silver image on gelatin will clean it successfully while the same treatment on a cellulose nitrate (collodion) based negative will destroy it if the solvent is alcohol). Such topics are discussed in the report of a presentation by Hill. -- AATA