What is the difference between trays and drums?
Paper, and sometimes sheet film, is usually processed in trays or drums. A tray is just a flat, shallow, lidless pan that you can fill with chemicals and drop paper into. A drum is like a developing tank, usually light-tight, cylindrical with end caps. You put the paper into the drum, then pour the chemicals in, then roll the drum around for agitation. Trays are most common in B&W work because you can use an adequate safelight with them. Drums are more common in color work because trays are much more difficult to use in the dark, but drums (the ones rated for daylight) can be used in room-light conditions.
