B&W vs Alt Inkjet Negs

[mkochsch]

Something that's been niggling at the back of my mind for a while. I've found that making a suitable negative for variable contrast B & W using Colourised RNP negatives is actually more demanding on the printer (needs darker more saturated inks) than making a negative for say a process like Cyanotype II. The thing that bugs me is that the "exposure scale" is shorter for B & W (say 1.2 to 1.65 logD) than the Cyano II process (which is closer to 1.8 to 2.10 LogD). Is this just because of the "Self-masking" effect? DOP vs POP?
~m

 

[Katharine Thayer]

Hi Michael,
I can't answer your question, but I think it relates to the question I was driving everyone nuts by asking repeatedly a while back, "What is the relationship between the blocking color, the DR, and the ES?" I was confusing myself for a while by thinking the print tonality had something to do with it, but even after I got that straight in my head (although it still makes no sense to me that print tonality isn't even in the equation) the question was still there unanswered. I finally decided that, for gum at least, there's no relationship, or the relationship is arbitrary and unique to each combination of printer, light source, etc, and there's no general law or principle that relates these things.

After reading your question above, I got to puzzling about why it is that when I spent some time determining blocking color for a number of different pigments, I found that all the pigments produced identical color charts (in other words the same blocking color would be indicated for all of the pigments I tested) when it seems to me that different pigments should have different ESs. But after reflecting on that for a while I suspect, but don't know for sure and don't have time to do that test, that since for that test I used my stock pigment mixes, that are mixed by eye to color saturation, that those particular mixes may actually have equal ESs. Another thing that makes me suspect this is that when I used a mix that wasn't mixed to saturation, it resulted in a different blocking color.

No answers, just more questions,
Katharine

 

[mkochsch]

I think it's the self-masking effect. What little I've been able to find seems to point in that direction.
I think in answer to your question the charts are similar or very close with different pigments because of the relationship is between the light source and the negative material whether it's colourised or not. What I've been noticing with gum is that the colour of the pigment affects the exposure more than the ES (contrast). My exposure for Lamp Black is 15 minutes but my exposure for Quinacridone Red is 3 minutes.

 

[Katharine Thayer]

I think in answer to your question the charts are similar or very close with different pigments because of the relationship is between the light source and the negative material whether it's colourised or not.

I remember your great illustration showing that that's the case. But... well, never mind; I'll save that annoying question for the moment.

What I've been noticing with gum is that the colour of the pigment affects the exposure more than the ES (contrast). My exposure for Lamp Black is 15 minutes but my exposure for Quinacridone Red is 3 minutes.

That might depend on the pigment concentration, I think, or on the color saturation. My exposure for lamp black is also much longer than my exposure for quinacridone red, but I print lamp black at a much deeper color saturation than I print quinacridone red, because when I print lamp black I print it in a saturation to produce a reasonable one-coat gum, whereas when I print quinacridone red, it's always as one layer in a tricolor gum print, so the saturation is chosen to accommodate the other layers.

How the amount of actual pigment compares is an unknown in the equation; lamp black is a very powerful pigment (not much pigment is required for a deep color saturation) whereas quinacridone red is in the medium range as far as pigments go, so you can't judge the pigment concentration by the color saturation. None of us who use paint, whether we carefully weigh the amount of paint or whether we mix by color saturation as I do, can have any idea how much actual pigment there is in our mixes, since pigments vary by pigment strength and paint manufacturers vary by how much pigment they put in a tube of paint. So the only way we could ever come to any understanding of the relationship between actual pigment/gum proportions and any other variable would be to use powdered pigment. That's not an experiment I'll ever be doing, as I hate working with powdered pigments, but I'd be glad to see the results if anyone did do that experiment.
kt

 

[Katharine Thayer]

What I've been noticing with gum is that the colour of the pigment affects the exposure more than the ES (contrast). My exposure for Lamp Black is 15 minutes but my exposure for Quinacridone Red is 3 minutes.

Michael, is this with the same quinacridone red (PR 209) pigment mix that you used for the HSL chart you showed a while back? That was rather undersaturated, as I recall. I'm trying to make sense of the contradictory theories, assertions, and observations around gum, color, exposure and curves, many of which don't fit with my own observations.
kt