Grain clumping, a controversial issue

[Photo Engineer]

I have been struck by the many comments here and elsewhere about grain clumping. I have been searching my library and other resources on this topic, and find no authoritative sources that say it takes place but several that say it does not, and they offer proof.

The closest I can come to a literature reference is this paraphrase, which I believe is from one of the works by Ross, to be cited below. Basically, he contends that some people claim to have seen clumps when viewing a film but what they are really seeing are the inevitable statistical patterns we see when we look at thousands upon thousands of grains stacked vertically. When we look at a cross section, they are separated into distinct grains. The first photo below is an example of looking down through a black dot on a film. You can see an indistinct edge made up of what appear to be clumps. Well, I'll get into that later on here.

F. E. Ross, a scientist working at Kodak in the 20s was tasked to find out several things that related to astrophotography. Basically, the astronomers wanted to know if silver metal particles could move horizontally in film as they had observed some movement due to the Kostinsy effect in spectrograms.

Kostinsky effect

The development effect in which dense image points are inclined to move apart, relative to each other, and light image points to move together, relative to each other. This occurs because developer is not being equally distributed over the image point and is rapidly exhausted when to heavily exposed image points are close together.

http://www.swpp.co.uk/glossary/kostinsky_effect.htm

http://books.google.com/books?id=WX8...effect&f=false

Ross has written several papers and books on the subject of the movement of silver metal images and particles in gelatin and shows that silver metal just does not move very far. He has studied tanning developers and ordinary developers over a pH range that would satisfy most of us and he did his work on glass plates to insure that the dimensional stability of films of that era was not interfering.

This was summarized in the book above and in his article "Film distortion and accuracy of photographic registration of position." I've attached photos below.

Photo #1, looking down at a small circular exposure showing what appear to be clumps around the edges (see comments above)

Photo #2, cross section of the same exposure using a tanning developer and showing the tanning effect in lower gelatin layer thickness.

Photo #3, cross section of the same exposure using a non-tanning developer. The gelatin has expanded in this case.

Photo #4, cross section showing two identical exposures processed in a tanning developer

Using this type of measurement, Ross was able to show that the images or parts thereof moved less than 2 microns from the original site of exposure. There was no evidence of clumping.

In Photo #5, I have produced an aggregated emulsion by using a low level of gelatin. Now, you may call this clumping as well. You can do this in 2 ways. You use too little gelatin for conditions when you make an emulsion or you use too little gelatin when coating an emulsion. Either way, grains coalesce and "clump" or "aggregate" and you get pepper grain. You see, when a grain touches another grain before or during development and forms a larger "lump", you get fog which is what you see in this print. This is how clumping appears in a print. White dots are seen. They can be virtually any size from the equivalent of several grains up to thousands of grains of Silver Halide.

I would like to thank those who helped me in off-line exchanges on this topic. In particular, I would like to thank AgX for his mention of Kostinsky. And for his permission to use this from our off-line discussion. In the articles I have, Ross does not mention Kostinsky.

PE

[Hexavalent]

Thanks for that post Ron. The x-sections do tell the tale.

[Alan Johnson]

It is well known, and anyone can try it for themselves,that as developer pH is increased the size of the observed grain increases.This is attributed to swelling of the emulsion and grain clumping.
If you deny grain clumping you need another explanation for the increase of observed grain size with pH. So what is your alternative explanation?

[Ian Grant]

This is isn't really related to grain clumping/micro reticulation caused by temperature variations during processing which we know exists but varies significantly depending on the particular emulsions used, and also the pH of the developer which is also unrelated to tanning effects.

Grain clumping is independent of pH & temperature (as long as tightly controlled) and more a combination of factors, emulsion type, developer formulae, and temperature variations. The very fact that it does occur and particularly with Tmax 400 & Neopan 400 means as Alan says there's a need for quite a different explanation.

My own gut instinct is that the hardening of many emulsions has lead people to be complacent about temperature controls, when I began film developing in the early60's films were very much softer, with far less hardening and you had to keep tight temperature control or you got full blown reticulation. Modern film hardening controls this meaning greater tolerance to changes, but with some developer/film combinations the hardening becomes weakened. Developers with a high pH containing Hydroxide seem to be an issue, but Hydroxide is known to soften Gelatin etc.

So we have a current situation where many films are quite robust but a handful aren't, processing has to be tight enough to be safe to prevent micro reticulation/grain clumping with films like Tmax 400, Neopan 400 etc.

Ian

[Mark Antony]

Count me in as another doubter of ' physical grain clumping' in all the journals I've read state that the grains don't move together but rather the shape and how the grain grows gives the visual effect of clumping.

Grains start out as crystaline shapes and with certain developers can form into what Mees called a 'spongy amorphorous mass' looked at though a microscope this looks like wire wool.
It is these types of grain viewed though the several layers that give the impression of 'clumping'.

Mark
PS My understanding of the Kostinsky effect is that as fine detail increases in frequency it's density falls.

[Ian Grant]

Count me in as another doubter of ' physical grain clumping' in all the journals I've read state that the grains don't move together but rather the shape and how the grain grows gives the visual effect of clumping.

Grains start out as crystaline shapes and with certain developers can form into what Mees called a 'spongy amorphorous mass' looked at though a microscope this looks like wire wool.
It is these types of grain viewed though the several layers that give the impression of 'clumping'.

Mark
PS My understanding of the Kostinsky effect is that as fine detail increases in frequency it's density falls.

Then how do you explain how films of the same type, processed in the same developer, stop bath and fixer and washed with the same water can vary from one set being fine grained as expected and the other having such excessive grain that they were unusable.

The films were Tmax 400, the developer Xtol replenished, Acetic stop bath and Hypam fixer.

The ONLY variable was attention to the temperature of all stages of the process, the films I processed 35mm Tmax 400 (fine grained) the rolls of 120 Tmax 400 were processed by another photographer using my chemistry. I did notice he didn't take a temperature reading for the wash water, it was a cold spell at the time in the UK.

Grain clumping/Micro reticulation exists but Kodak's research assumes stable and repeatable processing temperatures, all research requires tight tolerances so none of the published research shows it

Plenty of others have seen the same problems most just don't realise the cause, poor process control.

Ian

[Michael R 1974]

I've been interested in this topic for a while as up until the last year or so (better equipment now), I had realistically been unable to keep processing temperatures (particularly during wash) tighter than +/-2C. I can now keep everything within +/-1C, but there have been occasions in the past when I wasn't as careful and was never sure if the level of "graininess" in my negatives was "normal" or higher than normal for the film I have always used most often, Delta 100. I'm referring here to the grain I see in 35mm negatives developed to normal contrast. I always used Perceptol and DDX (ie not high PH), followed by a standard acetic acid stop bath before fixing and then washing.

There were threads on temperature-driven micro-reticulation before, but no real conclusions. Obviously it depends on the film. Some posters we adamant that virtually ANY temperature variation during processing results in some degree of micro-reticulation, however small. Others said generally with modern films the temperature variation would have to be quite large to have any observable impact. Then of course there's the issue of what type of temperature variation - ie slow drift while in a particular solution, vs a "shock" when moving from one solution to another with different temperatures. Additonally, the sequence of temperature shifts might also have an effect (warmer to cooler vs cooler to warmer etc).

My conclusion (or lack thereof) was that for my film, ideally Ilford would perform detailed tests to determine how Delta 100 is or is not impacted by different types and magnitudes of temperature shift during processing, and then be very clear in their processing recommendations. As of now their instructions on this are quite vague and generic for all films (ie keep processing temperatures within 5 degrees) and it is difficult to know if this recommendation is based on tests of individual films or just common sense in avoiding extremes. I'm not faulting Ilford in particular as Kodak and others are similarly quiet on the issue. Perhaps this is because there is no practical issue with modern films, perhaps not.

I'm still confused, although the post by photoengineer is very interesting indeed.

Michael R.

[Mark Antony]

I'd imagine that in that case the grain rather than physically clumping by moving in the body of the emulsionis is due to one or more differing perameters changing grain shape.
Both James and Vanneslow noted this effect, it can happen with too much agitation or too higher temperature, but the grains aren't moving though the emulsion they're physically changing shape (although when they change they can touch other grains).
The filaments grow because of the difference in charge at the tips of the filamentry structures.

I think that Kodak has tested (I know this because I've spoken to Kodak engineers) T max films at a variety of temperatures, one engineer told me candidly that the Gelatin in Tmax films was so hardened that reticulation was almost impossible and that the team couldn't get it to happen at 50°C+ the idea of grains physically clumping though a body of an emulsion is unlikely due to temperature.
If you have observed that, it would not be in accordance with Kodaks testing or my personal experience.
Regards
Mark Antony

[Alan Johnson]

LFA Mason, Photographic Processing Chemistry p120 notes:
"Graininess is also often worse at high pH values, due partly to the rapid development of the coarse grains and partly to the greater spread of the silver filaments into the much softer gelatin"
Jacobson & Jacobson,Developing p53 note:
"As the development proceeds,it is seen that the reduced silver in the two adjacent grains bridges the gap between the and so forms one large irregular grain..."
Maybe for brevity these processes may be lumped together and called grain clumping,this appears quite consistent with the view that it is not caused by the movement of the grains through the emulsion, it is a matter of the definition of "grain clumping" perhaps.

[Ian Grant]

It's not temperature itself Mark, all manufacturers test films at a variety of temperatures it's excessive variations and is only now seen with a handful of emulsions.

I process Neopan - Acros 100 & 400, at 26-27° C with no problems, no increase in grain (same with Tmax 400 when I used it) however others have posted of excessive grain with Tmax 400 & Neopan 400 and even full blown reticulation and the emulsion frilling off the base with the Neopan.

The question of why seems to be purely down to variations in control of process temperatures. It falls outside Kodak/Fuji etc testing at various process temperatures because these test were done for machine processing where temperature control is typically +/- 0.2°C

Ian