"David Foy" wrote in message
news:cL3eb.24138$o21.14595@edtnps84...
I'm puzzled. Again, I'm away from my bookshelf and can't provide a
reference, but I believe it is discussed L.F.A. Mason, "Photographic
Processing Chemistry." Mason was Ilford's chief scientist and published
his
book in about 1960. Focal Press, of course.

According to Mason, these backings are added to films meant to be
processed
on long-roll processors which have a large number of spools ("bobbins")
over
which the film must pass. Complex processes like Kodachrome and early
movie
films involve many immersions and the film has to be carried through a
relatively large number of tanks. The backing's main function appears to
be
protecting the film from abrasion. Anti-static and anti-halation
properties
are bonuses. I believe the original backing of the type was a layer of
colloidal silver, which was probably long ago replaced with something
cheaper.

So this raises a question: is the water jet situated somewhere far
downstream in the process? Does it achieve its purpose by washing off a
backing which has already been loosened by contact with alkaline
developers?
If the backing is washed off at the outset, then Mason's explanation is
nonsense.

David Foy

Rem Jet backing was historically referred to as an anti-halation
backing. It also:

protects the back side from abrasion BEFORE processing
reduces static by providing conductivity (contains carbon)
provides lubrication (like graphite, especially important for motion picture
film)
requires a special processing step for removal
makes a big mess if you put it in a process without this special step.

The rem jet removal is normally the first step in the process, so it doesn't
provide protection during processing. The binder is soluble in alkaline
solutions such as developers so it must be removed before the first
developer.