643, 646, 650 and CBS-6 Silver Recovery Units

Most photographic, lithographic, and x-ray film contain silver. It is this light-sensitive silver that creates an image when the film is exposed to light or x-rays. As the image area typically covers just a portion of the film, only part of the silver is used. In fact, the unexposed silver must be removed from the film before the image can be formed. Unexposed silver is washed from the film in a fixer bath. With black and white positive films, the amount of silver diluted in the fixer can be as high as 80%. As a rule of thumb, exhausted fixer solution will contain between .1 and 1 Troy ounces of silver per gallon. It is important to recover this silver for the sake of a clean environment and its monetary value.