Self-masking - Ziatype (or Ware-Malde) vs traditional Pt/Pd?

[J 3]

I am excitedly trying to select my first set of pt/pd chemistry for print making and have a question I've not seen addressed directly. The Ziatype is a print out process, and so strongly self-shadows. And indeed, several mention that you can use higher contrast negatives than traditional pt/pd prints. Those same sources though also say the resulting print is 'virtually identical' to a pt/pd print baring the extended color tone options. But self-shadowing has other effects on the image because it's non-linear - the exposure curve becomes more logarithmic. This should have the effect of mapping a large range of exposures into a reduced range of densities in the shadows, making the image either rather dark overall, or low contrast depending on the exposures. The shadows would never clip but so many values get mapped so close that shadow detail is lost. With salt-prints it's so bad, that people deliberately expose prints in open shadows, to force the media into reciprocity failure (which has the effect of making the exposure curve more exponential, flattening out the response, and leading to better contrast with the right exposure time). But I've never seen anyone mention this for Ziatypes.

Is the self shadowing effect not as pronounced with Ziatype chemistry vs traditional pt/pd? Are Ziatype's just printed with different negatives to compensate? Are the contrast controls in the Ziatype just strong enough to overcome the effect? Or is the effect just part of the look.

Thanks much in advance.

 

[NedL]

I can't help with your question but I'm mulling over the idea that the effect from exposing salt prints in the shadows is a kind of reciprocity failure. Somehow that doesn't seem quite right, since you can make an extremely long exposure ( say, in the shadows with a paper diffuser over the printing frame ) and then hours later make an exposure in the sun which will behave very similarly to starting the exposure in the sun. I've subscribed to this thread and will read the answers you get with interest.

 

[nmp]

I would say "virtually identical" refers to the final chemistry in the print, not that if one prints both the traditional Pt/Pd and Ziatype with the same negative, you end up with similar-looking prints in terms of tonal range.

I think the answer lies in the the negative. With the right kind of negative, one should theoretically be able to compensate for any process related non-linearity. Even salt prints can give similar tonal range as a Pt/Pd print with the right negative. If you are doing analog negatives, its exposure/development parameters can be tailored up to a degree for the process at hand and the rest is done with the sensitizer chemistry by use of contrasting agents to do a more refined tweaking of the print characteristic to match the negative. On the other hand, if you are using non-analog means, the negative can be printed to precisely match a particular process, even a most self-masked one, to get the full range of tones desired.

 

[J 3]

Thanks much both of you! I apologize for the long reply in advance...
In regards to NedL's comments about salt-printing and reciprocity failure you might very well be right. Here is my current read on the situation which might be off. Let me know what you think.

First what you're describing with the diffuser seemed at first to be a slow speed version of pre-flashing (used to cut the contrast of a media), but reading it closer seems maybe (?) to be consistent with what I said... I don't know. If what your saying is "drop the exposure to really low levels and then later, put it in the direct sun and it's as if that first exposure never happened" then this is consistent with a pronounced cliff of reciprocity failure. The idea is because at those extremely low light levels, effectively the media looks even slower yet, and at those levels the media is left basically unexposed. The exposure in direct sunlight then occurs as if it was reacting to unexposed media. I do know from Primitive Photography that paper cuts out a lot of light (paper negatives). If you're not talking about this, and are not talking about pre-flashing, I don't know what your counter example is but would love to know.

As for reciprocity causing increased contrast in shadows there are 3 main differences between open shadow light and direct sunlight might cause the effect:

1) Open shadow light is more diffuse - This can have and effect on the way a negative reads because of the change in the way light bounces around. It's a subtle effect, and mostly seen with enlargements (different enlarger head designs) where the effect is magnified.

2) Open shadows might have a different color balance (into the UV) - A Sandy King article I read on UV sources seems to indicate that some media (like carbon) have different contrast curves based on different wavelengths. It's hard to judge exactly because the article didn't correct for exposure time, but at least for some media the effect seems to be there. I've got no reason to believe however that from a UV / deep violet perspective there is much of a difference in the balance between the two and wet plate is often done in open shadows as well - the effect seems to be the same as in visible light - the diffuse light softens the shadows on the subjects face. Still there could be a contrast effect from the spectrum balance.

3) Open shadows are substantially darker than direct sunlight. Here is where reciprocity could factor in, or not depending on the media. So for some media (often highly engineered ones, like Fuji Acros 100) the reciprocity fall off is so gradual that for the range brightnesses seen in a typical image it's response is linear. For others the effect increases with each additional stop less of light received, an effect of statistics and chemistry. There tends to be a range of brightness that behave linearly (baring self-shadowing effects) below which sensitivity rapidly falls off.

What is rarely talked about is that if the effect is sharp enough, and the light levels are around or below the linearity cutoff, different parts of an image will be in different parts of the reciprocity curve. So highlights (under dark parts of the negative) will receive less light and the effective speed of the media will appear much slower. The effect will be highlights will print brighter if exposure is set so that mid-tones are unaffected. Likewise the shadows are exposed to lots of light, and the media effectively behaves as if it were faster. So the shadows get darker than they would for linear media. The effect of lighter-lights and blacker-blacks with reduced mid-tones is exactly higher contrast.

For example lets say that for we measure light levels in L units and each unit is twice the light of the level before (so L1 is twice as bright as L0. L2 is twice as bright as L1, etc...).
We are trying to print a negative that has areas of that span 5 f-stops of density (so from base+fog to DMAX represents a 16x difference in the amount of light blocked). Lets call these D1 (thinnest) through D5 (densest) by an f-stop each.
Let's pretend that at L5 and above salt has no reciprocity. Self shadowing still occurs but that's and effect of accumulated density, not exposure levels.
Lets pretend below L5 salt gets worse by a full stop each subsequent L level. So at L4 it looks half as fast. At L3 1/4 as fast, etc.

Now if you expose in a light source that blasts through the darkest D5 of the negative to deliver L5 to that spot, then the salt would see L5 through L9 Levels. No reciprocity. Adjusting exposures we would get linear image except self-masking means we'll really get a logarithmic response. So instead of PD1-PD5 we'll get Log(PD1) - Log(PD5) where the base of the log is determined by how strong the self masking is. PD is for print density, to differentiate it from the densities of the negative. This will be a lighter, lower contrast image. If we increase the exposure for good darks, then most of the image ends up being dark with a few small highlights.

I'm going to fudge the math a bit here for the reciprocity failure case. Say we now exposure in light that takes the darkest part of the the negative (D5), and exposures the print to L0 light levels. So our light source is 1/32 as bright, or 5 f-stops down. If we increase exposure times by 32x the print gets the same light level, but there is still a problem. At L0 - L4 brightnesses our media is 1/32 - 1/2 as sensitive respectively. So we give our print 5 more stops (1024x the exposure total. From a 10 min exposure to a 2h 50m say). The print reacts as if (relative to the first print).
D5 areas - react as if they saw 1 unit of light (exactly like the original case)
D4 areas - received twice as much light as D1, but media acted twice as fast as D1 as well. So 1*2*2 = 4
D3 areas - received twice as much light as D2 areas but the media acted twice as fast. So 4*2*2 = 16
D2 areas - " = 64
D1 areas = " = 256 (the original example only effectively saw 16 times as much light in these areas)
We've now created the effect of having a negative with 4 extra stops of density range. This will radically help counteract the logarithmic self shadowing term. Depending on the base of that term it may counteract it completely.

For visible light photography open shadows are often closer to 3 f-stops darker than direct sun (don't know what it is for UV). If that held for UV then reciprocity would have to be taking hold with salt, because you have to increase exposures a lot more that 8x to get a correct exposure. A negative can easily have 5 f-stops of density too. So the only thing that's required for this effect is for the reciprocity to be different over smaller than a 5 f-stop range.

Anyhow, that's how I think it works, and why contrast improves salt-printing in the shade. If someone know otherwise, or has a different theory / data, I'd love to learn.
Thanks everyone.