Pt/pd Printing - Making a test strip

[Alan9940]

Not to want you to change anything, but if you lay down a blank film, a stouffer negative and your paper, and exposing over time, won't the first step of unchanging black be your minimum exposure time (Calculated from actual time)? Or am I out to lunch?

Not sure exactly what this setup would look like, but, basically, when determining a Standard Printing Time you want the first exposure (that is, minimum time) needed to render black through film the same as uncovered paper. Therefore, the way I try to do this with pt/pd is to coat my paper, lay a piece of unexposed film along the coating at about the halfway point, then run a series of test strips across the paper. If it all works correctly, you should have a series of increasing density strips along the film next to paper black (well...as black as pt/pd can render.) The strip on the film side that matches the uncovered paper side is your SPT. Going forward, all negs will begin with the SPT exposure, then adjusted from there as needed.

Sure is a lot harder to describe this than it is to do it.

[Alan9940]

The thick 4-ply might be throwing a shadow, thus no sharp line...especially separated from the paper by the glass of the contact print frame. I use strips of rubylith.

Yeah, I thought of that. Do you mean standard red rubylith?

[koraks]

I used rubylith before I figured out that simple tinfoil works great as well.

[Vaughn]

Yeah, I thought of that. Do you mean standard red rubylith?

Red or amber both work. Tin foil, as suggested would also work, tho might throw a lot of reflected light around (but might not be significant). The rubylith is nice to use since one can see thru it for easy placement.

[koraks]

I see no problem with light scattering when using tinfoil, but I only use it for masking, so it's in direct contact with the negative. I glue a piece of tinfoil to a sheet of paper and rhen cut to size. The paper base probably helps with scattering if the foil is placed on top of the glass of the contact frame, particularly if you use a non-reflective paper base (matte black).
For exposure step tests I've used corrugated cardboard in the past, works like a charm as well. I think a plastic film bag should do the trick also.

[Christopher Barrett]

I use Cinefoil quite a bit on set for lighting. It's basically a roll of matte black aluminum foil. Could have a ton of darkroom uses.

25 bucks at B&H or your favorite photo/cine supply house

[Alan9940]

Thank you all for your help. I think I'm going to try black matboard (hopefully, this will eliminate light scattering and reflections) and, if that doesn't work, I may give the Cinefoil a try. Thanks, Christopher, for the link.

[Colin Graham]

I had this problem with my vacuum frame, so I cut sensitized paper into strips and spaced them far-enough apart in the frame to eliminate shadow bleed from the card.

The thick 4-ply might be throwing a shadow, thus no sharp line...especially separated from the paper by the glass of the contact print frame. I use strips of rubylith.

[jim10219]

Not sure exactly what this setup would look like, but, basically, when determining a Standard Printing Time you want the first exposure (that is, minimum time) needed to render black through film the same as uncovered paper. Therefore, the way I try to do this with pt/pd is to coat my paper, lay a piece of unexposed film along the coating at about the halfway point, then run a series of test strips across the paper. If it all works correctly, you should have a series of increasing density strips along the film next to paper black (well...as black as pt/pd can render.) The strip on the film side that matches the uncovered paper side is your SPT. Going forward, all negs will begin with the SPT exposure, then adjusted from there as needed.

Sure is a lot harder to describe this than it is to do it.

I've tried this before, but I ran into a problem with this method. However, my problem was with Cyanotypes, not Pt/Pd printing, and I was using digital negatives.

Basically, I found out I could get 100% density at around 10 minutes with my UV light source. The problem was, that exposure was so long that I couldn't get any midtones. My only options were pretty much all exposed, or all unexposed. I tried using various colors of ink for UV blocking on my digital negatives, but unfortunately the ones that blocked enough UV light to leave areas unexposed after 10 minutes didn't allow me to create smooth transitions from 0-100%. I couldn't figure out a way for Photoshop and my printer to keep the proportions of the max density ink the same throughout it's curve. So for example, it might start off at 100c, 100m, 100y, 100k. But by what should have been 50% density (and read as 50c, 50m, 50y, 50k), I was getting outputs like 30c, 8m, 15y,70k. And then my printer was imparting it's own curve over that because I have several different tanks for each of those colors Photoshop was recognizing (magenta, light magenta, etc.), none of which seem to block UV the same. So in order to get the smoothest curves with the most usable midtones, I had to switch to using black ink only, and to considerably shorten my exposure time. Now I'm exposing around 4 minutes and getting about 97% of the max density, but am able to achieve a much smoother and more usable curve while only sacrificing the last few % points of density.

Obviously with a different setup, you'll get different results. And maybe with film negatives it wouldn't be an issue. But that is why I have to use a step wedge when determining my max exposure times with my equipment.

[tgtaylor]

The bulk of my alt printing these days is in the shade with a short hit of sunlight at the end. I find that although it takes a little longer it gives a much better result than all sun. It would be difficult if not impossible to achieve the same result with a UV light box.

Thomas