Interesting marks on contact print

[Martin CF]

A colleague printed some 8x10 large format neg contact prints (on 8x10 paper) yesterday in the darkroom. They simply placed the neg on top of the paper, no glass, and blasted it with light from a De Vere 203, to expose the paper.

For some reason, there's consistent mottled marks across each print. The marks are not on the negatives, no glass was used. So, naturally, we think it may be dust/haze/fungus from the lens since, it's the only consistent factor (other than the paper).

However, the marks don't show through on the same enlarger lens when doing normal prints i.e. enlarged negative in the enlarger head.

Can anyone cast any thoughts or science my way?

 

[Willyekerslike]

I cannot be certain that it is the lack of a good heavy sheet of glass that is the problem because I havenever contact printed without a sheet of glass. I would try as a first step repeating a contact print or two with a good heavy sheet of glass holding everything down. There must be a reason why everyone and their brother has been doing it with a paper, negative and glass sandwich since contact printing started.

Regards....W

 

[Lachlan Young]

Probably from poor contact between the neg and paper & reflections caused by that. You really have to use a glass contact print frame with 8x10 to get good contact between film and paper - just watch out for Newton rings.
Alternatively, the paper not being sufficiently immersed in developer can cause all sorts of strangely uneven development. Seeing the print in question would help.

 

[E. von Hoegh]

Check that the condensers in the enlarger are clean.

 

[MattKing]

Probably from poor contact between the neg and paper & reflections caused by that.

And in addition to the reflections, also from the fact that where the negative is farthest from the paper, the image will be most blurred.
Was the enlarger light focused, or de-focused?

 

[Martin CF]

Thanks for all the responses. It transpires that one last print was made with the glass on top. The same mottled effect still appeared. Interestingly, I did a few 4x5 neg contact prints this morning, and no marks. Confusing!

 

[Martin CF]

I'm running with two other theories at the moment:
1. Paper batch defects (the marks are all in the same place)
2. Somehow, the lens was perfectly focused to show any dust and haze (it's a reasonably old Leitz 50mm lens which does need a clean) in focus on the paper.

 

[Lachlan Young]

I'm running with two other theories at the moment:
1. Paper batch defects (the marks are all in the same place)
2. Somehow, the lens was perfectly focused to show any dust and haze (it's a reasonably old Leitz 50mm lens which does need a clean) in focus on the paper.

Both are relatively unlikely, uneven development of the 8x10 is a more likely culprit - closely examine the neg, or scan it & any defects of that nature will show up.

 

[voceumana]

When using an enlarger as a light source for contact printing, you should NOT focus the light from the enlarger. Out of focus will provide a better diffuse light source. This might not be the issue here, but it is a good practice.

 

[Martin CF]

When using an enlarger as a light source for contact printing, you should NOT focus the light from the enlarger. Out of focus will provide a better diffuse light source. This might not be the issue here, but it is a good practice.

Yep, the lens wasn't intentionally focused. It may have *by chance* been in focus without anyone realising. Apparently the marks where across different negatives as well. Not artefacts could be found on the actual negs.

 

[MattKing]

You may have actually focused on the light source - it is amazing what dust on the surface of a light bulb looks like,

 

[Svenedin]

You may have actually focused on the light source - it is amazing what dust on the surface of a light bulb looks like,

+1

I was once making a whole series of paper test exposures and exactly this happened. There was no negative involved just the paper. I really scratched my head about it. I thought the paper developing chemicals might be exhausted so I changed them but it carried on. I then thought the paper might be at fault but it was the same on different paper. Then I cleaned the condenser and swapped out the bulb. The problem disappeared. I also checked the lens. There was some dust in the lens but that was not the cause. I don't know how I managed to focus on the bulb (or condenser) but it happened.

 

[Martin CF]

Thanks all. I think I'll settle on that answer then, as it feels the most plausible. Lesson learnt!