Expose to develop delay time

jongcelebes · Aug 31, 2009

Just got a cheap enlarger ($35 with 3 lenses) - cannot resist even tough I don't have any space to set as darkroom.

For a couple of days, I did my own BW printing. My enlarging (dry) and developing (wet) space is separated. So, what I do is - expose a paper, put it into dev tank and after I was done with it, I went to my bathroom in second floor to develop it. Time delay for the paper about 15 to 30 minutes. So far, I can manage a "so-so" prints (yeah, it's from 35mm to post-card size...).

Well, is there any rule about delaying paper development? Is my workflow will make any effect rather than directly develop after exposing?

Thank you.

RalphLambrecht · Aug 31, 2009

jongcelebes said:
For a couple of days, I did my own BW printing. My enlarging (dry) and developing (wet) space is separated. So, what I do is - expose a paper, put it into dev tank and after I was done with it, I went to my bathroom in second floor to develop it. Time delay for the paper about 15 to 30 minutes. So far, I can manage a "so-so" prints (yeah, it's from 35mm to post-card size...).

Well, is there any rule about delaying paper development? Is my workflow will make any effect rather than directly develop after exposing?

Thank you.

Given time, the latent image will weaken, and there will be less image to be developed. The critical time depends on your materials, but consistency is the key. As long as the time from exposure to development is consistent, your workflow is consistent. I suggest to make several identical exposures on one piece of paper with doubling time delays, which are are close to your working procedures (maybe 2, 4, 8, 16, 32 minutes). Then take them up and develop them to see what difference the time delays made.

Nicholas Lindan · Aug 31, 2009

jongcelebes said:
Well, is there any rule about delaying paper development?

There isn't any, as far as I know. It was common for package printers - high school yearbook photographs, for instance - to make a few hundred prints on a roll of paper that is run through a processing machine several hours later.

Film exposures on slow B&W film have a latency period measured in years. I imagine the same would be true of paper - however you should probably keep the paper tightly wrapped and minimize air exposure if you are going to delay processing much past a day or so.

RalphLambrecht · Sep 1, 2009

Nicholas Lindan said:
There isn't any, as far as I know. It was common for package printers - high school yearbook photographs, for instance - to make a few hundred prints on a roll of paper that is run through a processing machine several hours later.

Film exposures on slow B&W film have a latency period measured in years. I imagine the same would be true of paper - however you should probably keep the paper tightly wrapped and minimize air exposure if you are going to delay processing much past a day or so.

The latent image stability with film is amazing. Paper does not have the same stability. I don't know how long it will last, but the difference in speed and contrast between a 0 and 32 minutes delay can be seen in a side-by-side comparison.

Nicholas Lindan · Sep 2, 2009

RalphLambrecht said:
The latent image stability with film is amazing. Paper does not have the same stability...

That's an eye-opener. Seems like 3-4 minutes would be a maximum time - very interesting.

Retract my post above ...

Martin Aislabie · Sep 2, 2009

RalphLambrecht said:
The latent image stability with film is amazing. Paper does not have the same stability. I don't know how long it will last, but the difference in speed and contrast between a 0 and 32 minutes delay can be seen in a side-by-side comparison.

Ralph, are you going to share all this wonderful info with us in the new book?

Please

Martin

RalphLambrecht · Sep 2, 2009

Martin Aislabie said:
Ralph, are you going to share all this wonderful info with us in the new book?

Please

Martin

Only if you say 'please'.

Of course I will. The book will be ready for the printer in three months.

jeroldharter · Sep 2, 2009

RalphLambrecht said:
The latent image stability with film is amazing. Paper does not have the same stability. I don't know how long it will last, but the difference in speed and contrast between a 0 and 32 minutes delay can be seen in a side-by-side comparison.

I can only state my experience with Kentmere FP VC and Kodak Polymax papers. When doing a project, I often expose final prints in series of 5-10 and store the exposed paper in a paper safe. I sometimes have 30-50 sheets of final prints to develop. As luck would have it, sometimes I have had to wait a week or even two weeks before I could get back in the darkroom to process the prints. I could discern no difference to my eye.

What type of paper shows such a speed loss in just 32 minutes?

RalphLambrecht · Sep 2, 2009

jeroldharter said:
I can only state my experience with Kentmere FP VC and Kodak Polymax papers. When doing a project, I often expose final prints in series of 5-10 and store the exposed paper in a paper safe. I sometimes have 30-50 sheets of final prints to develop. As luck would have it, sometimes I have had to wait a week or even two weeks before I could get back in the darkroom to process the prints. I could discern no difference to my eye.

What type of paper shows such a speed loss in just 32 minutes?

Jerold

This test was conducted in April of 2003 with Ilford Multigrade-IV FB for latent image times from 8 seconds to 4 hours. The speed loss was 0.05 log exposure after 32 minutes in Zone VIII density (0.09 absolue reflection density), which is roughly 1/6 f/stop of exposure. I'm certain one would not see that unless a side-by-side comparison is made.

Latent image stability is related to reciprocity failure, and hence, most obvious in print highlights (where it was measured). It will be different with different papers and possibly different developers, but I see no reason to expect drastic differences.

Some darkroom workers have reported that they saw a difference between test-strip densities and final print. I suspect that most of these reports are caused by latent image stability or the lack thereof, if a number of test strips were made in sequence but developed simultaneously.

To be certain, I suggest to conduct this test for ones own materials, but it is advisable to keep the time between exposure and development constant in order to ensure consistent results.

jeroldharter · Sep 2, 2009

Thanks Ralph. I too will be buying your book!

RalphLambrecht · Sep 2, 2009

jeroldharter said:
Thanks Ralph. I too will be buying your book!

Jerold

Thanks for the word of confidence, but my last post was unfortunately incorrect. Your post mentioning speed 'loss' got me a bit off track (my mistake). The speed curve dipping into the negative means that less exposure was needed to get the same print density, of course. Therefore, we are talking about a speed 'gain' with time. This happens for the print highlights but to a lesser degree to the shadows, which explains the extended log exposure range, meaning loss of contrast. It's a bit like a fogging exposure, if you know what I mean.

I remember discussing this with Ilford at the time. I'm not sure that the underlying effect is clearly understood. It was explained to me as 'propagating' exposure.

Sorry for the confusion, I had it right in the book manual (sigh of relief).

Mr Bill · Sep 2, 2009

Ralph, I'll also be looking forward to getting a copy of the book. Wish I had known about it years ago!

In the meantime, I can add another twist to your method; I'm something of a veteran of latent image testing.

When making your test exposures, with a long time between first and last, it's possible that your exposing device (enlarger, in this case) has shifted; that is, the exposure right now vs the exposure one hour ago are different. If you want to confirm there is no change, this turns out to be very difficult to do. One might suggest to make all of the exposures at once, then process periodically. In this case, the possibility exists that the processing condition has changed somewhere between start and finish of the test.

A way around these possible shifts is to expose everything at the same time, and later process everything at the same time. But how do we get the latent image shift? Well, it turns out that freezer-temperature storage will virtually halt latent image shift. Yes, you can do more tests to confirm this, but it's a reasonably safe assumption with conventional materials.

So, the entire procedure is this: expose some test strips, perhaps 30, for example. Randomly pull out about half, for evaluation of consistency of your exposure and processing. People who've done statistical process control will appreciate the point of this. Quickly get the remaining samples into a freezer, obviously(?) light-tight water-proof containers are used. Then, at intervals, remove samples from the cold storage. Finally,process all samples together.

The evaluation seems relatively straightforward. I think it goes without saying, but let me say it anyway, if the "control group" of prints has more variation than the "latent image test" group, then nothing is known about the latent image shift, except that it is less than the normal "noise" in your process.

The usual result is that the greatest changes happen fairly quickly, then the rate of change slows down more and more.

ps; I wouldn't test this far in my own darkroom, but in industry, etc, it's a good way to go.

Nicholas Lindan · Sep 2, 2009

I started a test about three hours ago. The protocol is -

6 5x7 sheets of paper were contact printed with a step tablet over half their surface.
The sheets are stored in their black plastic bag along with a small stock of unused paper.
At intervals, the other half of the sheet is contacted with the same step tablet with the same exposure. The light source is stable and closed-loop.
The sheets are developed promptly after the second exposure.
Any difference between the two step tablet images on the same sheet should be due to latency effects, as the two images are developed at the same time.

So far sheets with 1/2 hour and three hours of latency have shown no visible change. Sheets from the all three (0, 0.5 and 3.0 hour latency) exposures show no sheet to sheet differences so developer effects don't seem to be coming into play, though aged developer is first apparent in shadow density and not in the highlights, whereas the latentcy-fog is in the highlights.

The next sheets will be at 16 hours and then again at 48 hours.

I have, however, noticed the effect Ralph mentioned - a sort of self-evolving fog. I had an Jobo LED safelight shining over the paper trimmer. The safelight passed all fogging tests. However, when I used paper that had been trimmed under the safelight, it exhibited fog if it was used after a few days of sitting loose in the paper safe. After changing the safelight to a Kodak OC filtered light there is no more 'trimmer fog'.

This whole thing is getting curiouser and curiouser... It is possible that the storage conditions - as regards exposure to air between exposure and development - may have some bearing.

Mr Bill · Sep 2, 2009

Nicholas, it sounds like a well arranged test. My only concern would be with respect to stability of your light source, but I'm not real knowledgeable about the electronic control systems. My feeling is that you are, so I presume it's a solid system.

That speed gain mechanism seems very odd. I could have used that on film, back in my younger days, when I was pushing film as much as I could for available light shots.

Nicholas Lindan · Sep 2, 2009

On with the test results -

The 3 hour latency print is now dry, and shows a definite increase in the highlight speed of the paper, clearly visible to the eye.

jongcelebes · Sep 2, 2009

Dear all. I can't saying - thank you for answers and knowledge.

RalphLambrecht · Sep 3, 2009

Mr Bill said:
Ralph, I'll also be looking forward to getting a copy of the book. Wish I had known about it years ago!

In the meantime, I can add another twist to your method; I'm something of a veteran of latent image testing.

When making your test exposures, with a long time between first and last, it's possible that your exposing device (enlarger, in this case) has shifted; that is, the exposure right now vs the exposure one hour ago are different. If you want to confirm there is no change, this turns out to be very difficult to do. One might suggest to make all of the exposures at once, then process periodically. In this case, the possibility exists that the processing condition has changed somewhere between start and finish of the test.

A way around these possible shifts is to expose everything at the same time, and later process everything at the same time. But how do we get the latent image shift? Well, it turns out that freezer-temperature storage will virtually halt latent image shift. Yes, you can do more tests to confirm this, but it's a reasonably safe assumption with conventional materials.

So, the entire procedure is this: expose some test strips, perhaps 30, for example. Randomly pull out about half, for evaluation of consistency of your exposure and processing. People who've done statistical process control will appreciate the point of this. Quickly get the remaining samples into a freezer, obviously(?) light-tight water-proof containers are used. Then, at intervals, remove samples from the cold storage. Finally,process all samples together.

The evaluation seems relatively straightforward. I think it goes without saying, but let me say it anyway, if the "control group" of prints has more variation than the "latent image test" group, then nothing is known about the latent image shift, except that it is less than the normal "noise" in your process.

The usual result is that the greatest changes happen fairly quickly, then the rate of change slows down more and more.

ps; I wouldn't test this far in my own darkroom, but in industry, etc, it's a good way to go.

Mr. Bill

I was fortunate enough to receive 6-sigma black-belt training recently, so, I understand your comment. It makes a lot of sense to do the test this way.

My test was done (thank God for lab records) by exposing the first strip and timing the time to processing (8s). Then, doing the same for the next few (16s, 32s, 60s, 2min, 4min), after which the rest was exposed, one after the other, and stored in a light-tight drawer, where they 'waited' until it was their time for processing.

My L1200 is hooked up to a voltage stabilizer and the exposures are very consistent. Dektol 1+2 in a covered tray does not show any degradation within 4 hours and my basement darkroom temperature is also very consistent unless I remain in it, which will warm it up, but I did not do that in this case.

Nevertheless, your recommendations are very valuable indeed.

RalphLambrecht · Sep 3, 2009

Nicholas Lindan said:
On with the test results -

The 3 hour latency print is now dry, and shows a definite increase in the highlight speed of the paper, clearly visible to the eye.

Nicholas

It's very odd isn't it? But, I like that we are performing global darkroom testing at APUG now. This is all very interesting.

Storage conditions of the exposed paper are important. As I said above, my test strips where stored in a light-tight drawer until they were ready for development, which was opened, of course, to take out the next piece of paper. However, since they were sitting on top of each other, every test strip got the same few additional seconds of safelight exposure.

How did you manage to minimize additional safelight or processing light to get to the aged test strip while doing a second exposure on the same piece of paper?

RalphLambrecht · Sep 3, 2009

jongcelebes said:
Dear all. I can't saying - thank you for answers and knowledge.

Sorry for robbing your thread.

However, you have sparked an interesting discussion and test series. The answer must have been more than you expected?

jongcelebes · Sep 3, 2009

I mean, I can't say anything but thank you. I get info more than I need (and it's good).
This forums make people like me (no access to workshop/teacher) to taste darkroom experience. Even it might brutally wrong and unusual.

RalphLambrecht · Sep 3, 2009

Nicholas Lindan said:
This whole thing is getting curiouser and curiouser... It is possible that the storage conditions - as regards exposure to air between exposure and development - may have some bearing.

Nicholas

I have taken another look at my test strips, and I think to have found some evidence to say that additional exposure (safelight or otherwise) is not the cause.

Please take a look at yours. In mine there is no speed shift around the speed-point area (0.6 above b+f) to speak of. Additional exposure would have a more significant impact there than anywhere else, because the curve is very steep at that point. In my test, the speed shift is purely limited to the print highlights, which speaks for a photochemical effect.

Do you see the same thing in yours?

Nicholas Lindan · Sep 3, 2009

RalphLambrecht said:
I have taken another look at my test strips, and I think to have found some evidence to say that additional exposure (safelight or otherwise) is not the cause.

Please take a look at yours. In mine there is no speed shift around the speed-point area (0.6 above b+f) to speak of. Additional exposure would have a more significant impact there than anywhere else, because the curve is very steep at that point. In my test, the speed shift is purely limited to the print highlights, which speaks for a photochemical effect.

Do you see the same thing in yours?

No, I don't think safelight exposure has anything to do with it. The problem I had some years ago with a Jobo LED safelight was that the safelight wasn't really safe. It passed the standard test: first fogging a bit of paper, and then putting a coin on the paper and exposing it to the safelight for an extended period of time. However, it was fogging the paper, and if the paper had been left there for 15 minutes then maybe the fogging would have been evident soon after the exposure. As it was the fogging was only evident after a few days of latent image maturation.

I am quite sure there are no gross safelight fogging effects - the margins of the prints and the high density steps show no uniform fogging.

As you noted, the increase in density is all in the highlights. There seems to be no increase in density in the midetones - but I haven't put the test prints under a densitometer.

I may be using 'speed' in a way that isn't quite mainstream. In the Darkroom Automation system 'speed' is the amount of exposure needed to get a certain tone on the paper - each tone then has it's own speed, a paper's 'highlight speed' is the exposure required to get a highlight ZVII tone on the paper. The published speed for film is the amount of exposure required to achieve a 0.7 OD density (grossly simplified), in the DA parlance if you wanted 0.3 OD on the film then you would set the meter to the film's 'shadow speed'. The choice of the word 'speed' here is a bit unfortunate - 'sensitivity' would have been better.

RalphLambrecht · Sep 3, 2009

Nicholas Lindan said:
No, I don't think safelight exposure has anything to do with it. The problem I had some years ago with a Jobo LED safelight was that the safelight wasn't really safe. It passed the standard test of fogging a bit of paper, putting a coin on the paper and exposing it to the safelight for an extended period of time. However, it was fogging the paper, and if the paper had been left there for 15 minutes then maybe the fogging would have been evident soon after the exposure. As it was the fogging was only evident after a few days of latent image maturation.

I am quite sure there are no gross safelight fogging effects - the margins of the prints and the high density steps show no uniform fogging.

As you noted, the increase in density is all in the highlights. There seems to be no increase in density in the midetones - but I haven't put the test prints under a densitometer.

I may be using 'speed' in a way that isn't quite mainstream. In the Darkroom Automation system 'speed' is the amount of exposure needed to get a certain tone on the paper - each tone then has it's own speed, a paper's 'highlight speed' is the exposure required to get a highlight ZVII tone on the paper. The published speed for film is the amount of exposure required to achieve a 0.7 OD density (grossly simplified), in the DA parlance if you wanted 0.3 OD on the film then you would set the meter to the film's 'shadow speed'. The choice of the word 'speed' here is a bit unfortunate - 'sensitivity' would have been better.

I know what you mean with speed. The official speed point for paper is 0.6 plus base+fog density, which is unfortunate, because nobody prints that way. Making filters to that speed point makes them less practical than what they could be. I set the speed point to 0.09 absolute reflection density (usually 0.04 plus base+fog), where I see my Zone VIII, which I print for.

I have a question into Kodak and Ilford retired researchers. They may be able to shed some light (pun intended) on the story.

clayne · Sep 4, 2009

jongcelebes said:
I mean, I can't say anything but thank you. I get info more than I need (and it's good).
This forums make people like me (no access to workshop/teacher) to taste darkroom experience. Even it might brutally wrong and unusual.

I usually develop my sheets on an as-i-go basis. Not more than 5 minutes usually. Never noticed any difference with that time-range, of course. You might consider looking for a darkroom tray kit as well, as you can make use of vertical space at the expense of a little bit more care when transitioning trays.

Victor, glad to see you are getting into darkroom printing. It's the "other half" of the equation and so much more enjoyable than slaving around a scanner (even if it takes longer at times).

I hope to be back in JKT in December. I'll probably be bringing some 12x16 prints to Malaysia, but I may bring some prints for Monty. We should all get together. Take him under your darkroom wing. He has some amazing negatives - as do you.

RalphLambrecht · Sep 5, 2009

Well, I got some info from my retirement contacts, which I like to paraphrase for general consumption:

The phenomenon is known as latent image progression in papers to the more familiar latent image regression seen with films. It has hardly ever been discussed in the literature but is well known within the industry. The effect is an unwanted side-effect of the rhodium doping used in high contrast paper emulsions. The mechanism is that rhodium functions as selective desensitiser affecting the faster crystals much more than slower crystals, which has the effect of increasing the contrast. The rhodium atoms are electron traps that mop up photoelectrons generated by the exposure, but some photoelectrons escape these traps to form more latent image in the period between exposure and development. The effect is a reduction in contrast and an increase in density.

hope this helps

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