Re: Pyro redevelopment


Sandy King (sanking@hubcap.clemson.edu)
Sun, 14 Feb 1999 22:34:07 -0400


I was involved in that thread, along with Liam Lawless. I don't have the
e-mail exchanges any longer, but bleach/redevlopment is an effective way to
alter the density range of negatives. However, be sure to try it out on
negatives you can afford to lose first because negative harmonizing with
supra-proprotional reducers is a little trick. Briefly the procedure is
this.

1. Wash the original negative thoroughly.

2. Bleach the negative (takes 1-3 minutes). I use the following formula.
        potassium dichromate 8g
        hydrochloric acid 6cc
        potassium bromide 5g
        water to 1000ml
Quite a number of other formulas are in the literature.

3. Wash again very thoroughly, for about 15 minutes, to remove all of the
potassium bichromate. Or, wash for about three minutes, then place in a
sodium bisulfite solution for two minutes, then rinse again for 2-3 minutes.

4. Re-develop in PMK. Development time to reach a given density range
varies a lot with films so do this by inspection. I would suggest using a
clear tray over a light box so you can really see what is going on.

5. Pull the negative when it looks right and and place it in a stop bath.
If you have a densitometer take a reading to check the density range. If
not high enough at this point, briefly rinse the film and return it to the
developer.

6. With PMK the image redevelops rather slowly. Useful times are 5-10
minutes for reduced contrast, about 15 to the same contrast, and 20 or more
minutes to increase contrast. However, this may vary considerably depending
on film. If you don't want to use PMK try a slow acting MQ developer,
something like D76 1:3.

7. You can increase contrast of the negative even after dry with further
development.

If something does not work exactly as described don't be too surprised.
Liam and I have gotten rather different results following almost identical
working procedures.

Sandy King

>A few weeks ago, there was a thread on bleaching and redeveloping
>step-wedges with pyro. At the time, I had no need for the info and so
>didn't keep the messages. Now, in what I'm sure is a corollary to Murphy's
>law, I have a problem which might be solved by that very technique.
>
>Is there anyone on the list who still has these posts who would be willing
>to forward them to me?
>
>Thank you,
>
>Mitch Valburg



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