Hello Kevin,
I really know what you mean about wrapping your head around the process. It is
not too complicated though.
First of all : keep in mind that when light hits your film the bright parts get
exposed, the dark do not. When you process your reversal film you (1)
develop, (2) bleachthebright parts. You
do nothing to the black parts till then, also not when you (3) clear the
bleach. Then you re-expose the "half developed"
film to light and thus you are "burning" the film and "creating" the
dark parts. Then you (4) develop this part of the film that you just
re-exposed and the black parts of your composition finally become dark
on the film too. Then (5) you fix it.
This is how it works in some detail (a simple explanation):
B/W reversal processing has 5 steps as you know, here is what they do.
Step 1 - First Developer
The first developer develops your film as if it were a
negative. In negative processing the light hits the film and creates
"black" grain, a negative image. You could fix your reversal film after
the 1st developer and have a negative film. If you did that to your B/W
reversal stock you would have "cross-processed it (in
this case the fixer would make the unafected grains disappear and you
would have transparent areas on the film where the original image was
dark -like a negative film should be).
Step 2 - Bleach
When you developed the film during step 1 you caused a chemical reaction
to the grains that have been hit by the light, this reaction creates
dark silver grains. These represent your bright (highlight) areas, of the
original image you filmed. By putting your film in the bleach you are
bleaching away all the dark grains you created in the 1st development
(it is the bleach really where you REVERSE the film) and what is left
are the unexposed crystals. If you think of the image you filmed and how the
film would look just after bleaching it would be like this:
-The bright parts of the original image would have almost nothing there
(first they were developed, made into a black body of grains and then
bleached).
-The shadows, the completely dark parts of the original image, would be
full of unexposed crystals (they had no reaction to the 1st developer
since no light had affected them and subsequently they were not affected
by the bleach -which only wipes out the developed grain).
-The mid-tones of grey would be a mix of the two cases above.
Step 3 -Clear Bath
Nothing too complicated here: this bath clears away the stains of the pottasium
bichromate used in the bleach chemical.
RE-EXPOSURE
(This is the second important part for the real REVERSAL of the process). All
the unaffected
crystals (representing the dark in the real photographed composition)
will be finally affected and become completely exposed, meaning they
will get BLACK as hell. Important to expose this film long enough. You
cannot do it too long, you can only do it too short -and too short causes
dark grey instead of black. Obviously while you hold the film under the
light you will not see it go black, it needs to be
developed again.
Step 4 -Second developer
You now develop the finally exposed grain and create the black part.
Step 5 - Fixer
You fix and harden the image.
(it goes without saying, you got to wash between all baths).
Hope that helped, let us know off list if there is anything you still did not
get (and excuse my english)
Greetings from Athens,
VB for LabA
PS: While teaching this process we came to understand the fine details and
experiment with them and finally we discovered a way to do travelling matte
without an optical printer, simply by applying the fundamentals of the b/w
reversal process. So you are right to be curious about exactly how it works.
________________________________
From: Kevin Timmins <on-on...@hotmail.com>
To: frameworks@jonasmekasfilms.com
Sent: Wednesday, 18 January 2012, 1:44
Subject: [Frameworks] Black and White Reversal Film Processing
On saturday I attended a course at nowhere in London on Black and White
reversal processing which was excellent.
I'm certain I could develop tri-x (and other stocks) straight out the gate
now but I want to understand the process thoroughly. That is to say the
chemical process from first exposure, first developer, bleach bath,
re-exposure, second developer and fixer (I understand there are washes
and clearing bath in between these steps). My understanding of the
chemical process is a little patchy. Any links or help in allowing my
brain to wrap around the chemical process would be extremely useful to
me as I want to experiment.
Thanks
Kevin
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