Sheet film is large format and medium format photographic film supplied on individual sheets of acetate or polyester film base rather than rolls. Sheet film was initially supplied as an alternative to glass plates. The most popular size measures ; smaller and larger sizes including the gigantic have been made and many are still available today. Using sheet film To use sheet film, the photographer places a sheet of film, emulsion side out, into a film holder in the dark, and closes the dark slide over the loaded film. Next, the holder is inserted into a large-format camera, and the dark slide is removed from the holder. The exposure is made, the dark slide is replaced, and the film holder is removed from the camera. Notches Sheet films have notches cut into one short side. This makes it simple to determine which side is the emulsion, when the film is hidden from sight (in the darkroom, or inside a changing bag). When holding the sheet in "portrait" orientation (short side up), with the notches in the upper right, the emulsion side is facing the photographer. The notch patterns vary in size and layout; each type of film has its own distinct pattern, commonly referred to as a notch code, to enable film type identification. Developing sheet film Many photographers who use large-format cameras and sheet film do their own film processing. Some more professionally oriented photographic labs will process color negative and positive sheet film, but the "corner drug store" photolab generally can not. There are multiple methods that can be used. Tray processing The simplest method for processing sheet film is using trays. The equipment, one darkroom tray per processing solution, is easily available and inexpensive compared to most of the other methods. There is also a much lower volume of solution required when using trays - only what's needed to cover the films (though most film development chemicals have minimum solution-volume-per-film-area requirements, which may require use of more solution). The films are placed into the chemical-filled trays one every few seconds, and a stack of films is formed. Agitation is performed by "shuffling" the films; the sheet on the bottom of the stack is brought to the top and pushed down into the solution. The photographer shuffles through the stack at the same rate that they introduced the films into the processing chemical. With careful counting and practiced