The process is different for film than it is for plates, but I assume
most folks here use film, so I'll describe that process.
Some labs use forming gas which is a mix of Hydrogen and Nitrogen, we use
pure hydrogen and pure nitrogen separately.
The idea is to decimate the environment of the film and remove all excess
water and impurites so that the film is more sensitive to light, with
as little reciprocity change as possible. This is all really particular
to things like astral photography that have long exposure times. The
amount of sensitivity or effective stop variation depends on the film.
The process is really geared toward using Technical Pan film, which,
depending on how long you let the hypering process run, will give you
an increased sensitivity of up to 13x. You can hyper any film, but
plus-x pan is only about 2-3 times more sensitive after the process, same
for color fuji chromes, etc.
Essentially, you put your film in a vaccuum chamber, seal it, fill it w/
Nitrogen gas which is inert and flush out the Oxygen in the chamber. Then
you add pure hydrogen gas which scrubs out the remaining oxygen (thus
water) in the film... you increase the pressure in the chamber to some
ungodly amount, and soak the film in hydrogen for a few hours, letting
the chamber depressurize. Then you flush it out, flush through Nitrogen, and
refill with hydrogen gas. Then you increase the pressure again and this
time also increase the temperature to some amount, I don't remember the
exact amounts off of the top of my head. THe higher the amount, the more
push in the film, but the more explosive your mini hydrogen bomb is. Then
you bake the film for several hours, again, the length determing the
sensitization push. You then depressurize the chamber, flush through
with nitrogen and then keep your film chilled and the hypering will last
about 1-2 weeks.
I wouldn't recommend using this process for daylight film, as the speeds
involved don't necessitate it. It is also a process that involves
specialized equipment, obviously, and a fare amount of care to avoid
explosion as we are talking about combining pure oxygen and hydrogen
at high temperatures. The main idea is to increase the sensitivity of the
film so shots that might take hours can take minutes and thus
you don't have to worry so much about film fogging and reciprocity failure,
etc. Tech Pan is incredibly contrasty film. And while that can be
somewhat controlled depending on what ASA you shoot it at and what
chemical you develop it in, it is not very pleasing for normal subjects.
What are you trying to accomplish by sensitizing film?
Jennifer Kolar
jkolar@monsoon.colorado.edu