For someone new to 4x5 film developing you might come across the term 'taco method' of developing a lot. I'll try to outline it here with a diagram and describe how it works and why it is needed.

The problem: protection the sheet

First of all, this method is for people who want to develop their 4x5s in a rotary tank, such as the one I own, a Unicolor rotary daylight tank. You can put a sheet of 4x5 into the tank and develop the same way you would a 35mm reel, however, the negatives in a 35mm reel are kept snug and protected inside the reel itself. A sheet that is free-floating might become scratched, might end up pasted on the wrong side against the walls of the tank, or might get stuck to another sheet if you are developing more than one in the same tank at the same time.

Like all negatives, the 4x5 sheet has a sensitive layer, the emulsion, that took in all the light information to make the image. That side has to be protected and be open to all the chemicals. If something blocks it from the chemicals it may develop unevenly or not at all. Then it looks like the sheet above this paragraph.

Solution: taco method

One could get a dedicated 4x5 developing kit that hangs all of the sheets separately in a rigid frame but if you decide to continue using a rotary drum for development you can use the taco method.

Basically, by bending the sheet in a taco U-shape with the emulsion inwards, you ensure that there is space around the emulsion for chemicals and ensure only the outside non-emulsion surface will touch anything.

In order to keep it in the U-shape, you can use a loose hair band like in the diagram above. In total darkness, make the taco shape and then carefully loop the hair band around the outside.

Do not use a bare elastic. Some films, when developed, will allow the elastic to show up in the developing leaving a stripe across it. I have done this. But with a hair band that is covered by fabric or a cloth, this does not affect it significantly.

Once you have made tacos out of your sheets, insert them into the rotary tank obviously still in complete darkness. Try to make them fit snugly so that there is a minimum of movement. Even so, I developed two sheets in my tank and when I retrieved them after the rinse stage one sheet was in the top of the tank and the other one in the bottom. But they were unharmed.

*addendum: Steve Korn, a great photographer in Seattle, suggested to me that he gets good results by leaving in the center spindle in the tank to prevent the sheets from bouncing about.

When you start the developing process the taco shaped sheets can tumble and roll inside the drum but otherwise should be safe from each other. Some use up to three sheets in their drums. Obviously, this depends upon your system.

For more information you may want to read this Flickr thread which contains photos of someone taco arrangement.