Try not to laugh too hard at my stupid question: what is the difference between a positive film and a reversal film?
It seems to me that if I want to shoot 16mm, have it developed, and project the results, my only choice is Tri-X reversal. Anything else (such as color) involves copying from negative film, right?
not silly at all.
The movie industry has always used Negative / positive for productions that are shown to a lot of folks. no mater if for a theatre or the "industrial" films that used to be common in training and marketing, one negative and many copies.
"Home" movies where their was only one or two copies expected to be made were almost always done on reversal film - and this was the main forte of Kodachrome.
since the reversal stocks are getting hard to find, (with our fingers crossed that the lads in Italy at FilmFerrania will change that situation) the path for a personal movie in colour boils down to shooting a colour Negative like 7203, and having the lab make you a print from that. The term vearies with the lab but it generally is known as a Best Light work-print. The production guys would use the workprint to do their editing, and when they were happy would cut and splice the Camera negative to match, which explains the "work" part of the name. Best light just means that the lab will expose the print at what ever settings they think are the best compromise for the whole roll. (and for extra money you can have what is called a "timed work print" where they go though and try to give every scene the best exposure on the print, but that is of course a lot more labour intensive.)
Just stash the negative away and use the work print in place of the reversla movie you would have received in the past.
Only real GOTCHA is the Print will be on a Polyester base, so if you don't have a fancy Ultrasonic splicer, you will have to use Tape splices on it. And since it is a contact print, the image enulsion will be on teh other side of the film than a comera original, and so the focus will require adjustment if it is mixed with older reversal footage.
Prints form Negatives are also available from 7222 double-X and Orwo n74, and UN54 done as a negative. in B&W.
OH an black and white reversal besides Tri-X includes the UN54 as reversal, as well as the FOMA r-100, BUT the foma is not happy in the standard Kodak reversal process so you should check with the lab before shooting to see if they have a work around.