RemJet (was Q: processing Kodachrome 25 color slide to get B&W?)

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

"Richard Knoppow" wrote in message
nk.net...

wrote in message
...
I've heard that Kodachrome has a "backing" that has to be
removed in the processing. Is this what you are
talking about below and is this "backing" light tight? In
other words could you run 35mm Kodachrome
through a red window Bantam camera without paper backing?

Michael Scarpitti wrote:

Kodachrome films have a special
anti-halation backing that is NOT water-soluble (E-6 and
C-41 have
water-soluble antihalation layers).

Kodachrome has a backing of a material called Remjet. This
is a combination anti-halation and anti-static layer. Its
used on several types of motion picture film although Kodak
seems to be getting away from it in its newer MP films.
Remjet, as the name suggests, is removed by a high
pressure water jet at the entrance to the processing
machine. It can be removed manually by treating the film in
a mild carbonate solution and swabbing it off. If allowed to
go through a processing machine which does not have means
for removing it it becomes a sort of tar which is hard to
get out.
I don't know why this backing was used on Kodachrome. I
think Kodak would like to discontinue Kodachrome but it has
unique qualities which have kept it around for nearly
seventy years.
Home processing is not impossible but is impractical. The
Kodachrome process is very complex and some of the solutions
are very toxic. I have posted details of the process to the
group a couple of times in the past. I don't know if the
formulas for the current K-14 process are available anywhere
(I suspect they are) but the preceding K-12 formulas are
available in _Modern Photographic Processing_ Grant Haist
for those who are curious about it.
--

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Richard Knoppow
Los Angeles, CA, USA