Weird Stuff Going On With My Digital Negs

So, just for starting out: my negs are basically an inverted BW image printed on a Xerox.
Normally my negatives are printed over Canon Pro-film Copy on a Xerox VersaLink, the negatives work fine, have given nice results, but occasionally the wear "random paterns" of the drum appear, and are noticeable on my carbon prints. As my print times are very fast (3:30min) I decided to try architects parchment paper, and it printed fine, without any deffects (It's also cheaper). For these paper negatives I started my exposure times on 5 min, but it proven to be too much. I then tried to print for the same 3m30s, and highlights were still muddy and blacks basically the same. The last print was slightly lighter than the 1st, but very so. They don't show much difference, no as near as I would consider cor almost 1 stop. The thing I don't get is: why is this happening? I'm using the same printer, same sensitizer, same everything. The only change was the acetate for the parchment. Any help?

The ink is being absorbed into the paper and the paper is diffusing the light. That's a guess. The ink will sit more solidly on the surface of a transparency, which will also not diffuse the light (at least as much).

Don_ih said:

The ink is being absorbed into the paper and the paper is diffusing the light. That's a guess. The ink will sit more solidly on the surface of a transparency, which will also not diffuse the light (at least as much).

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I don't think that's the case. The Xerox uses a toner thermally melted to the surface, if I zoom in the negatives (both paper and acetate) you can see the halftone screen of the printer with no diffusion.

As a halftone screen, it's not very sensitive to exposure time; this will just affect the black point, but it won't change the tonal scale. The timer may simply not have sufficient covering power to block the light fully, causing the whites to remain muddy.

Chromium VI said:

if I zoom in the negatives (both paper and acetate) you can see the halftone screen of the printer with no diffusion

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Diffusion would be the light going through the paper. The light would not travel straight through as it would with a transparency. Like I said, it's just a guess.

I will do more testing, I just think it's strange as it used to work with prototypes, and those take much more time with the paper than with the acetate... probably something with different wavelengths. I will do some densitometer readings on monday at the uni.

Don_ih said:

Diffusion would be the light going through the paper. The light would not travel straight through as it would with a transparency.

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This would only be a problem if the contact between the negative and the tissue would be really, really poor. In principle it doesn't matter much (at least for highlight fogging) whether or not the base the negative is printed on diffuses the light a bit. It may make a difference w.r.t. dot gain though, but unless the substrate is really thick, I wouldn't expect the difference to be more than a few percent. And it still doesn't explain the contrast issue.

Chromium VI said:

I just think it's strange as it used to work with prototypes

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Prototype negatives for carbon printing specifically, or prototypes for/of something else?

Chromium VI said:

those take much more time with the paper than with the acetate

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The paper itself would block more light, so logically you need longer exposures to get through the base. But for the areas with density, there can still be problems with poor coverage and those can very well vary from one base substrate to another.

I only tried laser printed negatives a few times and very quickly gave up on them as I found that my (very, very old) laser printer produced woefully inadequate density.

koraks said:

This would only be a problem if the contact between the negative and the tissue would be really, really poor.

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My printing press makes enough pressure to flatten everything out, although I'm interleaving a thin sheet of acetate so the tissue doesn't stick to the paper

koraks said:

Prototype

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Sorry, autocorrection... *Cyanotype

koraks said:

But for the areas with density, there can still be problems with poor coverage and those can very well vary from one base substrate to another.

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I will measure the density tomorrow and post the values here. The printer is actually not bad, although the mesh is quite visible (it uses a line ht screen on AM) my local stationary shop also has a printer, and theirs have a much finer screen ( a dot one running both AM and FM at the same time) and price is the same: 0,03€/print.


This carbon print was made with a negative on the first printer on Canson acetate film.

Chromium VI said:

I'm interleaving a thin sheet of acetate

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This is a problem by definition for two reasons, that are interrelated: diffusion and dot gain. But if it works for you...

Nice print!