Unexpected fogging: Why is Red light failing where Yellow-Green is sufficient?

[Letters to Theo]

Hi everyone, this is my first post here, though I’ve been a long-time reader of the forum.

I’m looking for some help regarding darkroom safelights.

I’ve never had any issues using a classic light-red safelight—until a few days ago.

I recently developed a bromide-iodide paper that came out fogged under the red light. According to the datasheet, this paper 'is routinely processed under indirect safelighting with a wavelength of 575 nm and higher; the corresponding safelight colour is yellow, though yellow-green, amber, or orange are recommended.'

Is it possible for a red lamp, which has a wavelength well beyond 575 nm, to cause such problems?

Many thanks to anyone who can share their thoughts, and best regards to everyone.

 

[Paul Howell]

Most modern papers are safe under amber safelights, a few of the older papers are safe only with red. Slavich was safe under red and fogged under amber. So yes it is possible for a red safe to fog some papers. But filter need to be replaced, as filters age you need a weaker bulb. I think my Foma FB is safe with both amber and red. Are you using a new to you paper, or it this happening with a paper that you have processed under red in the recent past? If so the problem might with your safelight, the filter might need to be placaed or you could have small white light leak. You should also check to see if your enalrger has developerd a light leak that is being reflected on to the paper when being exposed.

 

[Paul Howell]

Oh, forgot to ask, have tested your paper? Cut a strip in total darkness, put in developer for at least 2 to 3 minutes, then stop and fix as usual. Should be paper base white.

 

[glbeas]

I would suspect the safelight is not giving you a clean red spectrum.

 

[koraks]

I recently developed a bromide-iodide paper that came out fogged under the red light.

What kind of paper and how old was it? Also, did you test it for fogging as @Paul Howell suggests? Ensure to test not just for visible fog, but also changes in contrast in the high values (low densities).

Slavich was safe under red and fogged under amber. So yes it is possible for a red safe to fog some papers.

Same for Foma, but this is the other way around and that actually is not as likely, since there's usually no clear reason why a paper's sensitivity would be higher in the red part of the spectrum than in the green part. For red (and IR) sensitivity, the emulsion would have to be specifically engineered, and to then cut out green sensitivity would require additional measures on top of that. So it's an unlikely combination esp. for a regular enlarging paper.

One possible explanation might be that the paper is essentially panchromatically sensitized, with comparable sensitivity to red and green. Since the human eye is much more sensitive to green light, it's possible to get the same brightness in safelighting with a lower absolute luminous flux. This could create a situation where the green/amber safelight remains just below the threshold of (severe) fogging, while the (inherently stronger, to create the same visibility) red light crosses this boundary. But in this case I would expect that the amber safelight also fogs the paper, but more subtly, by acting as a preflash exposure that flattens contrast in the highlights.

 

[Letters to Theo]

Thanks, everyone.

The paper in question is Foma Retrobrom, from a recently opened pack.

I’ve been using Lith developers with this paper for years under the same red light without any issues. (But that doesn’t count, since as far as I know Lith process doesn't suffer from safelight fogging.)

A few days ago, for the first time, I tried developing Retrobrom with a traditional developer, and that’s when the fogging appeared. I checked the datasheet and found it strange that red light wasn't mentioned under 'Safety Lighting'. In the datasheets for their other papers, Foma explicitly mentions red light if it is considered safe—whereas for Retrobrom, they only go as far as orange.

I am using the same red lamp to print on Ilford MG and Foma VC papers without any problems. The whites always come out perfectly clean. I should add that this red light is extremely dim; it takes a couple of minutes for your eyes to adjust just to see the outlines of objects.

I’ve found an old Paterson lamp with a yellow-green filter among my gear. Should I give that a go, or would it just be a waste of paper? Foma says “yellow-green, amber, or orange are recommended.”

 

[koraks]

. (But that doesn’t count, since as far as I know Lith process doesn't suffer from safelight fogging.)

This is technically incorrect, but you typically have more leeway since the paper doesn't develop to completion. So in practice you could approach it this way, but you may still run into problems under certain circumstances.

The spectral sensitivity is for this paper is explicitly included in its product datasheet:

As you can see, there's (virtually) no sensitivity beyond 550nm.

they only go as far as orange.

Not 'only' - they include orange. It's not ONLY red. See above for the explanation.

The whites always come out perfectly clean.

That's not a full proof of absence of fogging. A safelight test should include testing for effects on the high values/low densities of the tonal scale.

I’ve found an old Paterson lamp with a yellow-green filter among my gear.

It will perform no better than a red safelight, but given the difference in human spectral sensitivity, it may appear brighter at the same absolute brightness as the red light, so you may be able to get away with less light. However, since you also are more likely to hit some of the wavelengths the paper has some trailing sensitivity to, the net effect can still be that you increase problems instead of reduce them.

The TL;DR is that a red safelight works perfectly fine for this paper and the cause of your fogging will likely have to be found elsewhere, assuming that the red safelight really only emits red light. What kind of light is it? Is it an LED-based source or a white light with a red filter?

 

[Letters to Theo]

Thank you koraks, thorough as usual.

What kind of light is it? Is it an LED-based source or a white light with a red filter?

It's an old Kaiser lamp, a white light with an insertable red filter, in a plastic housing.

I still can't understand why Ilford MG FB Classic doesn't show any fogging though, especially as it is slightly more restrictive regarding spectral sensitivity.

Retrobrom's fogging is even more confusing because Foma claims: "Regarding its lower sensitivity the processed material can be exposed to this type of safety illumination [i.e. wavelength of 575 nm and higher] or to other equivalent one for longer period than by common types of the black and white papers."

My only options seem to be:

- When developing Retrobrom in a standard developer, move the tray even further away from the safelight.

- Buy a 10 W equivalent LED bulb, fit it into the yellow-green safelight, and see what happens.

 

[Paul Howell]

You can try to develop with the print face down for the majority of the time, just peeking at it on occasion to make sure you getting an image.

 

[AZD]

I would suspect the safelight is not giving you a clean red spectrum.

I agree, this is where I would start. Maybe try a different red source. Mine is an ancient deep red glass lamp that blocks out nearly anything but deep red. It has never fogged any paper to a degree that I can detect.

Although not directly related to your Foma paper, I did develop some Ilford Ortho film under this light for ~8 minutes and saw light fogging. However, changing film in a minute or so is completely harmless.

So maybe two possibilities: Not “red” enough, and/or red enough but too strong.

 

[pentaxuser]

So maybe two possibilities: Not “red” enough, and/or red enough but too strong.

From this conclusion above, do I take it that Foma Retrobrom is the exception to the usual red light safety recommendations? For some reason Retrobrom needs a lower level of red light intensity than the rest of the Foma range of all of the Ilford range?

If so I am surprised that Foma makes no mention of this in its info sheets or does it mention this in some fashion, even somewhat indirectly?

Thanks

pentaxuser

 

[argent_negre]

I used to have safeligths similar to yours. When I started using some Foma papers, I noticed that the contrast was way lower than the the Ilford ones, so I tested for safelight fogging using the Kodak method. This method allows you to determine the time you can have the paper under safelight conditions without fogging. It turned out that, with those safelights, any exposure would show up. So I switched to led red ligths, two strips. Very economical, more powerful and completely safe.

 

[Doremus Scudder]

lots of talk here when a safelight test and a test for fogged paper will tell the tale.

I'd recommend more testing and less talking

Doremus

 

[MattKing]

lots of talk here when a safelight test and a test for fogged paper will tell the tale.

I'd recommend more testing and less talking

Doremus

Yep!
Kodak Safelight Test - really boring, but very thorough: https://www.kodak.com/content/products-brochures/Film/KODAK-A-Guide-to-Darkroom-Illumination-K-4.pdf

 

[miha]

Since Foma papers are often used in my darkroom, I decided to purchase a Foma safelight two years ago: https://www.foma.cz/en/catalogue-safelights-detail-1094

As strange as it may sound, this is one of very few items I’ve actually added new to my darkroom over the past 30 something years.

 

[koraks]

I'd recommend more testing and less talking

If you look at the talk, you'll notice that it virtually unequivocally recommends the same testing you suggested.