Liam Lawless (lawless@vignette.freeserve.co.uk)
Fri, 22 Jan 1999 21:08:06 +0000
HI everyone,
I have heard that PMK is excellent for platinum printing, but Hutchings says only with the right film, i.e. one with "low inherent base fog" (because of the stain's relative opacity to UV), and suggests FP4+ as a good choice. In view of this fact, maybe Tri-X isn't the best choice for alt., but read on...
Since I feel this is something I ought to know about, I've been running some tests with Pd prints (Ware's method) of two Agfatrans wedges, one pyro-stained (by bleaching and redeveloping in PMK), the other straight. Visually, the densities of the two wedges look about the same (ignoring the colour difference), but they measure as follows:
STEP NO. STRAIGHT WEDGE PYRO WEDGE
1 0.08 0.20
2 0.20 0.42
3 0.34 0.67
4 0.46 0.89
5 0.64 1.06
6 0.79 1.24
7 0.93 1.44
8 1.09 1.60
9 1.22 1.77
10 1.37 1.96
11 1.54 2.17
12 1.68 2.33
13 1.75 2.51
14 1.89 2.67
15 2.02 2.82
16 2.16 3.06
17 2.29 3.25
18 2.44 3.40
19 2.57 3.48
The pyro wedge is fairly strongly stained, to roughly the same extent as Tri-X in PMK. These figures show that bleaching and redeveloping in PMK significantly increases density (as seen by the densitometer's blue channel), but remember that visually the two wedges appear similar. [Maybe this would be a good way of intensifying negs?]
I made a number of prints of both wedges in the hope of reproducing the full density range of both; this was easy enough with the straight one, but even an incredibly long 2-hour exposure through the pyro wedge only managed to get up to step 13.
I feel that the experiment has proved very worthwhile, and is worth repeating by anyone interested in this sort of thing. The first thing to note concerns the spectral absorption of pyro stain, the colour of which I'd describe as greenish-brown, more brown than green. The Agfatrans wedge has a black square at one end, containing six clear coloured spots: blue, green, red, yellow, magenta and cyan. The correctly-exposed prints have recorded the magenta spot in black, also the yellow spot in mid-grey, but none of the prints has recorded any other colour.
Is that weird, or what? Why did neither wedge record anything under the blue or cyan spots? Yellow glass used to be used for safelighting in the old days, but the yellow spot is obviously passing some UV. The cause, I discovered, is that the wedges are old and comparison with a new one showed that the yellow dye is slightly faded (though not very much), but something still doesn't seem right here: the magenta spot passes UV fairly freely, but magenta is in theory made up of blue and red, both of which seem to be opaque to UV.
But I don't imagine that the effect of the stain on spectral sensitivity is of great practical importance. Since it results in a much lighter print, the pyro stain is, for practical purposes, acting as neutral density to some extent - which must be counted a disadvantage - but this kind of developer has two great advantages.
An as yet unresolved problem I have with Mike Ware's process is that the lighter tones come out grainy and have a somewhat harsh appearance. Maybe it's to do with the absorption of the papers I've used (and I've only been doing the process about a fortnight!), but the fault is again evident in the straight wedge prints. There is some improvement with pyro - there is still some (but less) graininess in the highlights, but the tonality is very much smoother throughout the tonal range.
But the most striking difference of all is the exceptional separation between tones in the pyro wedge prints; the contrast is higher, admittedly, but the transition from one tone to another is incredibly sharp. The straight silver wedge prints a much longer scale of tones (for which reason a harder neg would normally be required), but the shadows in particular are not well separated in any of the straight prints. The pyro prints cannot be faulted for separation, anywhere in the tonal range. They have a real feeling of sharpness and clarity (and also of smoothness) that is almost entirely lacking in the straight prints which, by comparison, are flat and lifeless. [But, in case Mike W. is reading, I must say that they looked wonderful before comparing them!]
I've so far only printed step wedges, but my conclusion is that pyro negs appear to make a big and very worthwhile difference in this particular alt. process, but a strongly stained neg is going to require impossibly long exposure times unless it is very thin. I'd therefore concur with Hutchings' advice to find a film that doesn't stain too much. A heavily stained neg, such as Tri-X/PMK, is going to increase contrast, but I've played about with non-staining pyro formulae on ordinary camera film years ago and some of these gave results that are just as good as PMK (i.e. produce prints with the same qualities), so I suggest that they are also worth investigating by alt. workers. If anyone wants to try it, I can put up my own non-staining formula.
But I've digressed - the original point of this experiment was to compare the effect on printing of different silver and silver-plus-stain densities! How I have tried to do this is by comparing the tones of my prints and selecting those that give a reasonably close visual match; the step wedge densities that correspond to the matching tones can then be regarded as equivalent for printing under UV. (Obviously, only prints that have been given the same exposure are compared with each other.)
The approximate equivalents are as follows:
Silver+stain Equivalent silver
Density Step No. Density Step No.
0.20 1 0.08 1
0.42 2 0.55 4.5 (i.e. between 4 & 5)
0.67 3 1.34 6.5
0.89 4 1.09 8
1.08 5 1.37 10
1.24 6 1.54 11
1.44 7 1.75 13
1.60 8 1.89 14
1.77 9 2.02 15
1.96 10 2.29 17
2.17 11 2.57 19
2.33 12
2.51 13 Equivalents for steps 12-19
2.67 14 of the pyro wedge are off the
2.82 15 scale of the straight wedge
3.06 16
3.25 17
3.40 18
3.48 19
These figures illustrate the point made earlier, that softer negs must be made when a staining developer is used.
What all this means is that if we have a strongly stained neg, a density of 1.77 (for example) should behave like an ordinary silver density of 2.02 as far as UV transmission is concerned. Looking at the figures, I'd hazard a guess that a maximum of around 1.50 would be right for a strongly stained neg to be used in Pt/Pd or similar processes. But this table is probably not very useful because it would not apply to other films with different staining properties. (Furthermore, it is probably not very accurate because the patches look different under different light - the above assessment was under tungsten.)
I've passed all this on because PMK and pyro negs look very promising for alt. processes, though the stain is probably a little too strong (on Tri-X on any rate, though I'm not sure Carl W. would agree). But I expect that non-staining pyro developers will prove even more valuable, and intend to do more experiments in this area. I'll post my findings when I've found them, and would be glad to hear from anyone with relevant information.
Liam Lawless
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