High base fog, should I worry?

Fatih Ayoglu · Aug 23, 2023

Hi all,

Since I got my densitometer, I keep measuring things to understand the effects of any process or change on prints, films etc and then make correlations.

Today I’ve measure my recently developed film, Kentmere 400, pushed 1 stop, developed with Rodinal 1+25. The agitation was 1 min full and then 1 inversion at each 30 second mark. The base fog was 0.4

Initially I thought this was a fixer issue so I’ve collected some film trimmings and they all measure around 0.3 to 0.45

And I remember well that the fixer clearing time for undeveloped film was 1:30 and I’ve fixed the roll at least 3 mins with constant agitation.

So the question is should I worry about this? If I should what can I do to lower it to the levels of 0.05 like all the charts I’ve been seeing.

Cheers,
Fatih

Nicholas Lindan · Aug 23, 2023

If you are measuring Base + Fog then you need to remove the density of the base. Some films have a heavily tinted base to minimize halation, and processing can not remove this dye and lower the base density.

Strip the emulsion off a bit of scrap film so you can measure just the base. Soaking the film for a few minutes in a splash of Clorox in a bit of hot water works well.

Careful of falling into the trap of too much instrumentation. The goal, after all, is a photograph that can be hung on a wall somewhere.

xkaes · Aug 23, 2023

Fog (#1) is density created by developing the emulsion -- and varies with the emulsion and the developing. To determine Fog, you have to "discount"/subtract the Base.

Base (#2) is the density of the "plastic" and the unexposed & undeveloped and properly fixed emulsion.

As mentioned, each can be quite significant -- and together, much more so.

Compare #2 to #1 and you can see what you are dealing with. One might be much greater than the other.

Density from the base is easily overcome by increasing the exposure of the paper.

Fog can similarly be dealt with, but it's best to try to minimize it first.

Mr Bill · Aug 23, 2023

Fatih Ayoglu said:
So the question is should I worry about this? If I should what can I do to lower it to the levels of 0.05 like all the charts I’ve been seeing.

Hi, I don't know what charts you've been seeing, but my guess is that you're shooting 35mm film. Since this film typically has the end sticking out into the light it's possible for light to "pipe" into the end of film and go some ways into the roll. So it's traditional for such film to have some higher base density to "mop up" such light leakage. I'm guessing this is what you're seeing.

The diluted Clorox bleach, per Nicholas, is a standard test method.

If you were using something like cut sheet film, or perhaps 130-roll film, these never have a film end exposed to room light so no need for the manufacturer to build in a high base density. (Although it's possible that they might.)

Fatih Ayoglu · Aug 24, 2023

Nicholas Lindan said:
If you are measuring Base + Fog then you need to remove the density of the base. Some films have a heavily tinted base to minimize halation, and processing can not remove this dye and lower the base density.

Strip the emulsion off a bit of scrap film so you can measure just the base. Soaking the film for a few minutes in a splash of Clorox in a bit of hot water works well.

Careful of falling into the trap of too much instrumentation. The goal, after all, is a photograph that can be hung on a wall somewhere.

Hi Nicholas, thank you for this. It was purely to understand what it is to be honest. I dont measure any negative with denstitometer, bought it only to create dodge masks on ortho film per Ctein recommendation and thought I can give it a go. I will see if I can do what you suggest with Clorox.

xkaes said:
Fog (#1) is density created by developing the emulsion -- and varies with the emulsion and the developing. To determine Fog, you have to "discount"/subtract the Base.

Base (#2) is the density of the "plastic" and the unexposed & undeveloped and properly fixed emulsion.

As mentioned, each can be quite significant -- and together, much more so.

Compare #2 to #1 and you can see what you are dealing with. One might be much greater than the other.

Density from the base is easily overcome by increasing the exposure of the paper.

Fog can similarly be dealt with, but it's best to try to minimize it first.

Thank you, I read some developers are better than others to clear the fog.

Mr Bill said:
Hi, I don't know what charts you've been seeing, but my guess is that you're shooting 35mm film. Since this film typically has the end sticking out into the light it's possible for light to "pipe" into the end of film and go some ways into the roll. So it's traditional for such film to have some higher base density to "mop up" such light leakage. I'm guessing this is what you're seeing.

The diluted Clorox bleach, per Nicholas, is a standard test method.

If you were using something like cut sheet film, or perhaps 130-roll film, these never have a film end exposed to room light so no need for the manufacturer to build in a high base density. (Although it's possible that they might.)

Hi Mr Bill. I have done the measurement on a 35mm negative, from a pure unexposed area, complete black on a print and that has read 0.4. Then I have found some scrap ends of 120 films, you know when you shoot them there are usually 1 or 2cm at either end, not exposed, they read pretty much the same. After all I have compared my home developed negatives to lab developed negative form back in 2019, and they seem fine to me. Maybe the charts I am seeing, like on Ilford technical bulleting are drawn when the base has been taken away.

All in all, all my negatives are printing well and I have not encountered any issue, yo my best knowledge but was just wondering.

Fatih Ayoglu · Aug 24, 2023

Nicholas Lindan said:
Strip the emulsion off a bit of scrap film so you can measure just the base. Soaking the film for a few minutes in a splash of Clorox in a bit of hot water works well.

Is Clorox a bleach technically? Sorry I am in UK and keep googling about it

PS I have stripped emulsion part of some scrap film, indeed I can get 0.05 to 0.07 density, pure for plastic, which is normal I think. Also I have tested further scrap film, some has as low as 0.2 HP5 120 some has 0.4 K400 35mm

All in all I dont think it does effect my printing except the higher the base+fog density, the more exposure it needs to reach max black.

xkaes · Aug 24, 2023

Fatih Ayoglu said:
Thank you, I read some developers are better than others to clear the fog.

You don't "clear" fog. You "avoid" fog formation.

xkaes · Aug 24, 2023

Fatih Ayoglu said:
All in all I dont think it does effect my printing except the higher the base+fog density, the more exposure it needs to reach max black.

You are correct. You don't need to scrape/clean the emulsion from it's base. You are always going to be exposing paper through a base PLUS emulsion PLUS fog.

You can determine this very simply, without any scraping, bleaching, etc. as I first outlined above.

Leave the scraping and bleaching for the pots and pans in the kitchen.

Fatih Ayoglu · Aug 24, 2023

xkaes said:
You don't "clear" fog. You "avoid" fog formation.

I think I meant some other developers create less fog because my understanding is the fog is also developer dependent

koraks · Aug 24, 2023

Fatih Ayoglu said:
Is Clorox a bleach technically?

Yes. However, in a photographic context, there's a big potential for confusion.
Clorox is a bleach in the sense that it can bleach textiles, dyes, stains etc. in a variety of applications, including general household use. It is NOT a photographic bleach in the sense that it will convert a silver image into a silver halide or a soluble silver salt. So it's not a photographic bleach. Coincidentally, Clorox (essentially a hypochlorite solution, often with a thickening agent) is aggressive enough on a gelatin emulsion to actually break down the gelatin strands, alloowing full removal of the emulsion. Any silver embedded in the scraps of emulsion, will still not be 'bleached' in a photographic sense, however.

TL;DR: Clorox is a household bleach, and a household bleach is a totally different thing from a photographic bleach.

In this particular instance, it's not really used as a bleach anyway, but just as an aggressive agent to destroy a hardened gelatin emulsion. Soaking in e.g. a sodium hydroxide ('Draino') solution would also work.

Fatih Ayoglu · Aug 24, 2023

koraks said:
Yes. However, in a photographic context, there's a big potential for confusion.
Clorox is a bleach in the sense that it can bleach textiles, dyes, stains etc. in a variety of applications, including general household use. It is NOT a photographic bleach in the sense that it will convert a silver image into a silver halide or a soluble silver salt. So it's not a photographic bleach. Coincidentally, Clorox (essentially a hypochlorite solution, often with a thickening agent) is aggressive enough on a gelatin emulsion to actually break down the gelatin strands, alloowing full removal of the emulsion. Any silver embedded in the scraps of emulsion, will still not be 'bleached' in a photographic sense, however.

TL;DR: Clorox is a household bleach, and a household bleach is a totally different thing from a photographic bleach.

In this particular instance, it's not really used as a bleach anyway, but just as an aggressive agent to destroy a hardened gelatin emulsion. Soaking in e.g. a sodium hydroxide ('Draino') solution would also work.

Yes, I got that it is not the Bleach we use in C41 process I'll give it a try only for experimental purpose to see which developer I use create different fogs on different films

Fatih Ayoglu · Aug 24, 2023

xkaes said:
Fog (#1) is density created by developing the emulsion -- and varies with the emulsion and the developing. To determine Fog, you have to "discount"/subtract the Base.

Base (#2) is the density of the "plastic" and the unexposed & undeveloped and properly fixed emulsion.

As mentioned, each can be quite significant -- and together, much more so.

Compare #2 to #1 and you can see what you are dealing with. One might be much greater than the other.

Density from the base is easily overcome by increasing the exposure of the paper.

Fog can similarly be dealt with, but it's best to try to minimize it first.

So basically if I put a part of the film straight into the fixer without exposing it to light, I can get the base value. It is difficult for roll films but I can do that for sheet film I suppose but then the value will be different compare to roll films as sheet film has a thicker base.

koraks · Aug 24, 2023

Fatih Ayoglu said:
It is difficult for roll films

Next time you process a roll film, when loading it onto the reel, just snip off the first half inch/centimeter and save that for your test.

Fatih Ayoglu · Aug 24, 2023

koraks said:
Next time you process a roll film, when loading it onto the reel, just snip off the first half inch/centimeter and save that for your test.

Thought about it, the key is taking that part form the changing tent where I put the rolls on the reels and put into the fixer. (Time to use my night vision googles )

Bill Burk · Aug 24, 2023

Fatih Ayoglu said:
PS I have stripped emulsion part of some scrap film, indeed I can get 0.05 to 0.07 density, pure for plastic, which is normal I think. Also I have tested further scrap film, some has as low as 0.2 HP5 120 some has 0.4 K400 35mm

That’s exactly what I would expect.

120 film comes with black paper backing so that film often has 0.05 Base. It’s base is clear plastic and anti-halation (prevents light from bouncing back after it goes through the film and adding a halo around bright objects) function is done by the backing paper.

With 35mm film that goes loose through the camera, gray permanent dye is often added to the base for anti-halation (0.2 to 0.4 is very reasonable).

The manufacturers know you can “print through” so the dye doesn’t hurt anything when you print.

It would mess with printing alt processes that need UV light to expose the print, and it would dim projection. So there are some films that don’t dye the base on purpose.

xkaes · Aug 24, 2023

Fatih Ayoglu said:
So basically if I put a part of the film straight into the fixer without exposing it to light, I can get the base value. It is difficult for roll films but I can do that for sheet film I suppose but then the value will be different compare to roll films as sheet film has a thicker base.

Don't try sheet film when you want to test 35mm film. They are sometimes different. Just clip a 1" piece of your 35mm film and stick it in fixer for 5 minutes. There is your base + emulsion. NO FOG -- and no need for bleach.

To test for fog, do the same thing, but develop the film first -- do not expose it. There is your base + emulsion + FOG.

Subtract the density of #1 from #2 and you know how much fog you have. No bleaching, scraping, convolutions, etc. needed.

Fatih Ayoglu · Aug 24, 2023

xkaes said:
Don't try sheet film when you want to test 35mm film. They are sometimes different. Just clip a 1" piece of your 35mm film and stick it in fixer for 5 minutes. There is your base + emulsion. NO FOG -- and no need for bleach.

Thank you, is it important if that bit is exposed or not? If it is important, once I clip that bit, I will transfer straight into fixer without turning any light in my darkroom (or I'll put in another dev tank seperately).

PS I know sheet film has a thicker base so the numbers will be different

xkaes · Aug 24, 2023

Let me clarify:

Just clip a 1" piece of your 35mm film and stick it in fixer for 5 minutes. KEEP IT IN THE DARK. DO NOT EXPOSE IT TO ANY LIGHT. There is your base + emulsion. NO FOG -- and no need for bleach.

To test for fog, do the same thing, but develop the film first -- do not expose it. There is your base + emulsion + FOG.

Subtract the density of #1 from #2 and you know how much fog you have. No bleaching, scraping, convolutions, etc. needed.

Fatih Ayoglu · Aug 24, 2023

xkaes said:
Let me clarify:

Just clip a 1" piece of your 35mm film and stick it in fixer for 5 minutes. KEEP IT IN THE DARK. DO NOT EXPOSE IT TO ANY LIGHT. There is your base + emulsion. NO FOG -- and no need for bleach.

To test for fog, do the same thing, but develop the film first -- do not expose it. There is your base + emulsion + FOG.

Subtract the density of #1 from #2 and you know how much fog you have. No bleaching, scraping, convolutions, etc. needed.

Thank you, I know I can be stupid sometimes

Saganich · Aug 24, 2023

For Kentmere 400 I measured 0.34 for base density plus fog pretty consistently in D23. This is similar to HP5 where I measure between 0.35 and 0.42. For TriX I measured 0.22-0.25. So, I don't think anything is wrong per se.

retina_restoration · Aug 24, 2023

Kentmere has a significant base dye density - it's built in to the film. Have none of you USED Kentmere?? The base density is irrelevant in practice.

ic-racer · Aug 24, 2023

In my experience testing, base fog 0.40 eats into the dynamic range of the film. This diminishes latitude.

Of course it depends on your subject matter and intentions, but, depending on your printing skills, you could still get good prints with that fog level. My old film around 0.6 I’m just saving for the packaging and historical interest; no plans on using it.

Fatih Ayoglu · Aug 24, 2023

I am a rather keen hobbyist rather than anything else and if one day if I ever manage to sell a print, that will be from MF or LF with films like Pan50, HP5 or Foma 100 and I’ve tested all, they have half or third of what Kentmere has.

xkaes · Aug 24, 2023

retina_restoration said:
The base density is irrelevant in practice.

If you use more than one film, you have to adjust for the base density in order to achieve MAX black.

MattKing · Aug 24, 2023

High base density also affects our ability to visually assess our negatives.
That isn't in any way an insurmountable challenge - but it does take some practice.

High base fog, should I worry?

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