What starts as a simple reel of film gains complexity when you need to put it on rewinds or in a projector and determine the correct orientation, particularly considering that film might not only be on a reel tail out but also oriented so the image would read backwards when viewed through a projector, editing machine, or loupe. Below are some snippets from various sources on determining winds and on rewinding.
A and B Wind
A-Wind and B-Wind – The emulsion position of the film. There are two sides to a piece of film, and there are also two possibilities — camera original is B-Wind, while a print struck from it will be A-Wind — because film is printed emulsion against emulsion. In order to tell if a piece of film is A-Wind or B-Wind, hold it up with the emulsion facing you. The image will read correctly if it is A-Wind, but if it is B-Wind it will appear as a mirror image (so when looking at the film you’ll need to find text or some other object in the image where you can determine the correct orientation). You can’t mix A-Wind and B-Wind material, unless you want things to appear as a mirror image or soft in focus as a result of being printed base-to-emulsion.
Q. What is the difference between A-wind and B-wind?
A. Wind refers to the relationship between image direction and emulsion position. Images on the film that are “B-Wind” read correctly through the base. Images on the film that are “A-Wind” read correctly through the emulsion. All camera negative original is “B-wind”. When you contact print your original onto an answer print, the AP becomes “A-Wind”
A Wind: When you hold a roll of 16 mm or other single-perf film so that the film leaves the roll from the top and toward the right, the perforations will be along the edge toward the observer.
B Wind: When you hold a roll of 16 mm or other single-perf film so that the film leaves the roll from the top and toward the right; the perforations will be along the edge away from the observer.
Read more: http://motion.kodak.com/motion/Education/Film_Video_Glossary/index.htm#ixzz3IPokiAl8
It is extremely important to wind film evenly and with sufficient tension to provide a tight roll. If the roll is not tight and smooth, it can suffer edge breakage during shipping and handling. When you rewind, be careful that the winding machine is properly lined up so that the film feeds smoothly and squarely from one reel to the other, leaving no protruding edges. With console type motor rewinds, proper alignment should be part of the original design, but check the appearance of a wound reel to determine whether some further adjustment is necessary. If winding for long term storage, always wind emulsion in to minimize stress.
There are some winding habits that seem deceptively helpful. Is one edge of the film riding against the reel flange during the winding operation.
Some bench rewinds are deliberately set out of line to obtain even winding by this method. Occasionally, shipping reels are sprung so much out of shape, that you may again be tempted to achieve even winding by flange binding.
The problem with the edge binding method is that sharp points are sometimes left on the rims of some metal reels when, for example, someone used pliers to remove a reel of film from a tight shipping case. A sharp point of this kind may cut the edge of the film on each turn of the reel.
Sometimes reels are bent or sprung to less than or considerably more than the film’s width. If so, the reel should be replaced. Much of the damage occurs when the reels are forced into shipping cases that are themselves damaged. If you must use defective reels and cases until replacements arrive, make every effort to restore them to a reasonably usable condition.
Read more: http://motion.kodak.com/motion/Support/Technical_Information/Storage/storage_handling.htm#wind#ixzz3IPmYvFfX
Historically, 35 mm release prints in the United States have been wound emulsion out when ready for projection. In this orientation, the film comes off the supply reel in a counterclockwise rotation but winds onto the projector take up reel in a clockwise rotation with the emulsion in. When 35 mm film is kept wound emulsion in exclusively, there is a tendency for reduced focus drift and other screeming problems.
There is no preferred emulsion orientation for 16 mm and 8 mm films since they are used in both emulsion positions. Original reversal films, such as those used in cameras, are wound emulsion out. Prints from negatives and reversal dupes are normally wound emulsion in. And, because thermal energy levels are only a fraction of what is encountered in theatrical projection, focus drift and other screen image problems are not apparent.
Read more: http://motion.kodak.com/motion/Support/Technical_Information/Storage/storage_handling.htm#wind#ixzz3IPkWfzzk
Head or Tail out?
For storage, some repositories wind films tail out (with the beginning at the core), so that films will have to be rewound, and presumably reinspected, before they can be viewed from start to finish?
NFPF, Film Handling and Inspection, http://www.filmpreservation.org/userfiles/image/PDFs/fpg_3.pdf