Liam Lawless (lawless@vignette.freeserve.co.uk)
Thu, 11 Mar 1999 02:25:47 +0000
Hi All,
First of all, I'm disgusted with the lot of you, ignoring Kevin's
contribution on
bleaching after all the fuss you made about sulphuric! I've tried his
suggestions today and while none works properly in its present form, I'm
sure he's leading us in the right direction.
Copper sulphate + citric acid does not bleach on its own, or if it does it
does so so slowly that I couldn't see it. With hydrogen peroxide added, the
film (a finished neg) was a fraction lighter after nearly two hours, but
this is probably a bit slower than we want. I didn't try adding nitric as
an accelerator because the point is to avoid not only sulphuric, but equally
evil substitutes.
Pot. permanganate + sod. chloride + acetic does bleach - very quickly - but
leaves a fairly strong orange-brown residual image which does not clear
(clear in 5% sod./pot. metabisulphite, though 5% sod. sulphite also seems to
work). This, I believe, is permanganate-stained silver chloride, as it can
be redeveloped.
The permanganate formula looks fairly promising. I haven't had time to try
today, but maybe using sod. sulphate instead of sod. chloride would solve
the problem. Any other ideas out there?
I've also been checking out ideas for contrast control. Again, I don't
think we've yet got quite what we want, but it looks like there might be a
better
ways of working. Before going into details, let me describe my control neg,
used as the basis for comparison. This was made by the reversal method,
exactly as described in P-F and on the list, viz. 5 minutes first
development in my home-made PQ, stop, bleach, wash about 10 minutes, clear 2
minutes 15 seconds, redevelop in original developer (without washing after
clearing). Did not bother to fix; final wash around 20 minutes. The test
subject was a Stouffer wedge, exposed for 3X the normal time and flashed 6
seconds at the same aperture.
This, I believe, corresponds to the way most of us are presently working and
thus gives a "normal" result (for the exposure/flash times I have chosen).
Densities of the first 12 steps (representing the approximate range of a
good camera negative) were as follows:
Step Number : 1 2 3 4 5 6 7
8 9 10 11 12
Original (Stouffer) 0.05 0.20 0.35 0.50 0.65 0.80 0.95 1.10 1.25
1.40 1.55 1.70
#1 (Control) 0.24 0.32 0.47 0.70 1.00 1.37 1.63 1.89
2.04 2.18 2.27 2.31
The exposure and flash times were fairly arbitrary, but the figures above
show the typical pattern for negs made on lith this way: the shadows and
highlights are flatter than the midtones since they occupy the toe and
shoulder of the curve respectively, and, in addition, there is a definite
point somewhere in the lighter midtones where there is a big jump in the
separation between adjacent tones. This is not a very good example of that
phenomenon, but it can be seen that the "distance" between steps quickly
increases from the lowest value (0.08, between steps 1 and 2) up to the
maximum of around 0.3, and finally tails off again. Differences at or near
the
maximum can be seen over a range of about 6 steps (i.e. 3 stops), which
represents the straight-line part of the curve.
Bleaching Back
Dave's idea a while ago was to make a much darker than usual neg by not
overexposing, and take it back to the required density range in a reducer.
Two negs were made, both with the "normal" exposure (i.e. without applying a
factor); one (#2) was flashed for 6 seconds (as per the control), the other
(#3) left unflashed. Processing was exactly as for the control, except that
with their larger amount of silver halides, the bleached and cleared films
took much longer to redevelop; they had to be left 15-20 minutes in the
developer. Reduction was in Farmer's, made up at about twice the strength
used for prints, though in retrospect normal strength would have been fine.
Before reduction, the densities were:
Step Number : 1 2 3 4 5 6
7 8 9 10 11 12
#2 (flashed) 0.61 0.89 1.23 1.54 1.79 2.00 2.14 2.24
2.31 2.33 2.34 2.35
#3 (unflashed) 0.75 1.21 1.77 2.36 2.90 3.43 3.90 4.26
4.48 4.60 4.63 4.65
Fog levels, as can be seen, were very high, but the fog clears quickly in
Farmer's, and the plan was to reduce until the density for step 12 looked
somewhere around 2.0. I'm not very good at estimating densities by eye, but
I decided that the reduction should be stopped - or had gone too far! - when
I noticed that step 2, the second lightest step, was as clear as the base.
This took about 4 minutes for #3, and 2 minutes for #2. After reduction,
the densities were:
Step Number : 1 2 3 4 5 6 7
8 9 10 11 12
#2 (flashed) 0.04 0.06 0.20 0.48 0.73 0.94 1.03 1.11
1.19 1.20 1.20 1.20
#3 (unflashed) 0.04 0.05 0.08 0.36 0.82 1.23 1.50 1.68 1.78
1.83 1.91 1.93
Thus it seems that there's no problem bringing the maximum density
down to the required value (if you can get it right!), but for both strips
separation is pretty awful at both ends of the scale. A super-proportional
reducer may improve matters, but I still don't see how it would help
highlight separation that was not really there before reducing - this needs
overexposure (the X-factor!) and doesn't happen without it.
Clearing Bath
Back when all this started, I spoke about the solvent effect of sod.
sulphite on silver halides; I hadn't measured the density loss that clearing
causes, but it seemed likely that the effect is greatest on the shadows
(where it's wanted least), and it occurred to me that maybe clearing could
be postponed until after redevelopment. Accordingly, a neg was made,
exposing and processing exactly as the control, except that clearing was
left until after redeveloping.
The neg looked pretty dirty before it was cleared, but cleared fine in a
couple of minutes (time immaterial when done this way). Densities were:
Step Number : 1 2 3 4 5 6 7
8 9 10 11 12
#4 (cleared later) 0.38 0.47 0.65 0.87 1.13 1.43 1.66 1.85 2.03
2.10 2.19 2.23
Again, b+f is high, but, surprising (to me!) is the fact that it is really
only the shadow tones that are darker in comparison with the control strip
(see figures for #1); steps 1-5 are all about 0.15 units darker than in the
control. Highlight separation still leaves something to be desired, and the
spacing between midtones has changed little (though it is, perhaps, a little
more regular), but the range is compressed without loss of highlight or
shadow detail, and the strong shadows seem a definite advantage. Possibly,
though, we would want to slightly modify exposure and flash times if
processing this way.
Low-Contrast Developer
My tests so far with low-contrast developer have used Sil Horwitz's D-512 PP
(phenidone-pyro) developer. Dave's LC-1 might have been a more useful one
to start with, but I was attracted by the combination of phenidone and pyro.
I understand that the formula of D-512 is in print, but I don't feel I
should give it out here without Sil's permission; I hope that at some stage
he will talk to the list about it.
I did not try a first development for low contrast because, as others have
suggested, I doubt if it would produce adequate highlight density (which
would lead, in turn, to very dark, foggy results on reversing). Instead I
used D-512 for the redevelopment stage. Four negs were prepared, again as
the control, and processed up as far as the wash that follows the bleaching
stage. Two of these were cleared before redeveloping, and two after.
Redevelopment times were 10 and 15 minutes, so that the films were:
#5: Cleared before redeveloping; redeveloped 10 minutes
#6: Cleared before redeveloping; redeveloped 15 minutes
#7: Cleared after redeveloping; redeveloped 10 minutes
#8: Cleared after redeveloping; redeveloped 15 minutes
After redeveloping, the films were all washed and fixed for 5 minutes.
Resulting densities were:
Step Number : 1 2 3 4 5 6 7
8 9 10 11 12
#5 0.15 0.24 0.32 0.50 0.78 1.13 1.43
1.74 1.95 2.13 2.25 2.33
#6 0.15 0.21 0.36 0.60 0.89 1.24 1.55
1.86 2.06 2.23 2.35 2.44
#7 0.20 0.27 0.43 0.64 0.92 1.22 1.46
1.66 1.78 1.90 1.94 2.01
#8 0.21 0.31 0.49 0.73 1.03 1.35 1.62
1.83 1.98 2.09 2.13 2.17
Highlight separation with this developer (if clearing before redeveloping)
looks about the best so far, but the shadows are worse than the control.
Clearing after redeveloping helps the shadows a little, but this gain is
offset by poorer separation at the highlight end.
Further Work
All of the films here (except one) used a 3X exposure factor to give the
strongest shadow detail, but for the best highlight separation a higher
factor is wanted. When an ordinary print developer is used, it appears that
the shadows can be strengthened quite considerably by clearing after
redeveloping; it is likely that this strengthening would permit a higher
exposure factor to be used to improve highlight gradation while still
retaining full shadow detail, giving the best of both worlds.
Sil's D-512 does not appear to have any significant advantages when
considering an original negative of normal range, but I expect it will come
into its own with very dense, contrasty originals... to be tried at a later
date.
Liam
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