Effect of Prewash On Developer Activity

[ic-racer]

The effects of prewash are sometimes mentioned. I was working on a development scheme for some film and needed to tame contrast.

The H&D curves presented show the film (SVEMA 42L) with and without a 3 min prewash of tempered H2O .

The gamma without prewash was 1.12 (red) and with the prewash the gamma was 1.05. The developer (T-max 1:4), temp. (24c) and time (3:00 min) were the same for both.

The effect is measurable, but subtle. About a 6% lowering of contrast.

The control strips were exposed with a Wejex sensitometer and measured with a calibrated Tobias TCX Densitometer.

 

[Mr Bill]

Hey, cool test, and good job of it!

If I may, I would hazard a guess that most of the effect is due to a slight dilution of the developer as a result of the water being carried into the developer by the wet film. But, just a guess - maybe or maybe not.

If you should ever want to investigate this idea it's possible to estimate the carryover by weighing a piece of scrap film when dry, then again when wet. Water weighs roughly 1 gram per milliliter as I recall. (Or, if you're using film on reels in a tank, there's probably also residual water in the tank/reels. )

FWIW if someone wanted to use a prewash and NOT dilute the developer, I'd guess it would be possible to deliberately over-concentrate the developer during mixing, just enough to counteract the amount of carried-over water per the volume of developer used.

Thanks for posting your test!

 

[bernard_L]

Hey, cool test, and good job of it!

+1

If I may, I would hazard a guess that most of the effect is due to a slight dilution of the developer as a result of the water being carried into the developer by the wet film. But, just a guess - maybe or maybe not.

Admittedly without quantitative justification, my feeling is that carryover from prewash and subsequent dilution is not at the 5% level. I would maybe propose that the developer penetrates more easily a dry emulsion, than one occupied by water, that must be displaced.

 

[john_s]

I'm wondering if your test revealed a worst case example; quite strong developer and quite short developing time. As Mr Bill suggested, maybe some significant dilution took place, and being such a short time, the time to displace the prewash water would have been a significant proportion of the development time.

I can't complain about the test procedure though.

 

[loccdor]

Thank you for the test. I prewash without adjusting any other parameters and to me this helps confirm what I observed: that there is no big change from it in time required.

 

[Don_ih]

I think you need to perhaps test at a lower temperature and for a longer time. 2 seconds out of 3 minutes is over 1 percent. Can you guarantee there was not a 3 or 4 second discrepancy between those development times?

Also, if displacing the water that has already soaked the emulsion takes any amount of time, the shorter the development time, the more significant that amount becomes.

If you used a fine-graduated cylinder to measure the water you poured in vs the water that came out, you would know how diluted the developer was. Did as much water as possible come out of the tank before pouring in the developer? My guess is no more than a few ml remained in the tank. Unless you diluted the tmax developer just once, you could easily have that much difference in dilution between two separate mixes of developer. (250ml +750ml of water vs 2 x 125ml + 375ml). Any mixing error would, again, be exaggerated by the higher-temperature, shorter development time.

 

[koraks]

This is a nice test, but in order to attribute any value to the difference observed, the first logical step to take would be to verify the methodology for any systematic errors as well as repeat the test N times to establish variance. Then see what difference remains after statistical analysis.

 

[Don_ih]

I think there's enough potential error in measuring time, temperature, and volume, to account for the results. Even the prewash step will change the temperature of the tank and what's inside - even if only as the room-temperature air goes in as the water goes out.

 

[ic-racer]

Here is some additional information:

Dry tank/reel = 210g
Wet tank/reel = 224g

'Extra' water at 1g/ml = 14ml

Dry film dilution = 28ml developer + 112ml water = 28/140 = 0.2 = 1:4
Wet tank dilution = 28ml developer + 126ml water = 28/154 = 0.181818 = 1:4.5

 

[ic-racer]

I'd be glad to run another test. But, I'm not sure what 'other' test would be needed. Does anyone do a pre-wash differnently than agitate tempered water for a few minutes then pour it out? Are people transferring the film to a dry tank or letting the film sit for some time? Or using non-tempered water or adding Photo-flo something else I could test?

 

[Mr Bill]

Here is some additional information

Thanks for measuring that!

So in this particular configuration it looks like the prewash step is adding roughly 14 ml water to a nominal 140 ml developing solution - so a dilution of roughly 10%. (I suspect the 14 ml is a somewhat rough number, depending on the drain time.)

I'd be glad to run another test. But, I'm not sure what 'other' test would be needed

If you're up for it, something that might be interesting would be to "undo" the extra dilution by reducing the water in the original developing solution. In other words, let that "reduced water," ~14 ml, be replaced by the ~14 ml of carried-over prewash.

Such a test seems like it MIGHT show only the difference between developing solution entering dry film vs entering a pre-soaked and "swollen" emulsion.

Thanks again for both running the tests AND posting!

 

[ic-racer]

Yes, good points, one could test if just diluting the developer might have the entire effect. The pre-wash, however, also tempers the film faster (3 min vs 5min dry temper).

My own personal concluion is pre-wash does not do much, and I only did it back in the 1980s then stopped after that, until this most recent test.

In terms of the original problem (taming aerial film contrast) I have been down this path before. Even adding ice to the Jobo (in bottles of course) to get the temp down to 18c.

Actually the next step is to see how these negatives with gamma about 1.0 will print. Might be ok because, in my experience, the multigrade papers I use don't have any probelm achieving low contrast.

 

[Milpool]

Interesting. I experienced the opposite (with D-76 and TMX), but I wasn’t testing for this. It was just something I came upon by accident while trying to determine whether or not pre-washing affected development uniformity.

 

[Chuck_P]

I'd be glad to run another test. But, I'm not sure what 'other' test would be needed. Does anyone do a pre-wash differnently than agitate tempered water for a few minutes then pour it out? Are people transferring the film to a dry tank or letting the film sit for some time? Or using non-tempered water or adding Photo-flo something else I could test?

With all my single bath (XTOL) developing of sheet film I've only ever pre-washed with gentle agitation for 60 sec. Why, I believe I read it in The Negative, or somewhere. I have always transferred directly to the developing tank to begin development immediately, and I'm using TMX, so I am very particular with the temperature, always beginning at standard 68F. Honestly, I don't know what difference there would be with my negatives without the prewash, but I appreciate you doing it. Why so long of a prewash?

I've recently started mixing my own BTTB, where in that process it was recommended to not use a prewash.

 

[Vaughn]

So no significant difference shown between pre-wet or not so far...

 

[chuckroast]

I'd be glad to run another test. But, I'm not sure what 'other' test would be needed. Does anyone do a pre-wash differnently than agitate tempered water for a few minutes then pour it out? Are people transferring the film to a dry tank or letting the film sit for some time? Or using non-tempered water or adding Photo-flo something else I could test?

First, thanks for taking the time to do this and share it. It's really interesting and nice to see a quantitative discussion of the topic.

As others have suggested, a longer development time might provide a better measure. Double-X at ASA 100 in D-76 1:1 for 7.5 min, for example. Tri-X similarly takes a fair bit of time in D-76.

When I still did a prewash, it was for 3 min with the film sitting in a running water bath at a nominal 20C. I stopped doing it after a LOT of back- and forth here which seemed to land on the idea that prewashing the film actually made it harder for the developer to penetrate evenly because it had to difuse into an emulsion swollen with water. If true, that would be consistent with your findings.

 

[chuckroast]

Yes, good points, one could test if just diluting the developer might have the entire effect. The pre-wash, however, also tempers the film faster (3 min vs 5min dry temper).

My own personal concluion is pre-wash does not do much, and I only did it back in the 1980s then stopped after that, until this most recent test.

In terms of the original problem (taming aerial film contrast) I have been down this path before. Even adding ice to the Jobo (in bottles of course) to get the temp down to 18c.

Actually the next step is to see how these negatives with gamma about 1.0 will print. Might be ok because, in my experience, the multigrade papers I use don't have any probelm achieving low contrast.

I have not done it, but I suspect aerial film contrast could be reined in with either D-23 or Pyrocat-HD in a two bath configuration. Beutlers might also be a good choice since it is strongly compensating.

 

[ic-racer]

Thank you for the suggestions on different developers. Stupid me...I have been using T-max developer at 1:4 ever since I started rotary processing in 1986. I forgot about the 1:7 and 1:9 dilutions. That will be my next test.

 

[Doremus Scudder]

I think the test, with the strong developer and short developing time, shows the effect of pre-soak quite well. I would imagine that the effect would diminish with longer developing times.

My supposition is that the saturated emulsion prevents the developer from soaking into the emulsion so quickly. The more gradual onset of development as the developer diffuses into the emulsion instead of being soaked up by it accounts for the slower onset (and maybe promotes more even development.

Note that any loss in activity at the beginning of development due to this effect can be easily compensated for by extending the development time a little.

Best,

Doremus

 

[dokko]

very nice test, thanks a lot for sharing!

I'd be curious though what happens if you simply extend the development time of the film with prewash a little bit to get the same overall density.

my guess is that the curves would match very closely with very little difference in gamma, maybe a slight difference in highlight compression.

 

[Vaughn]

...

my guess is that the curves would match very closely with very little difference in gamma, maybe a slight difference in highlight compression.

That was the basis of my earlier 'no significant difference' comment. One eventually determines the best development scheme by the results and how the negative prints. I also appreciate Doremus' observation that pre-wetting the emulsion does not negatively (and perhaps positively) affect the evenness of the absorption of the developer...just the rate. That has been my observation also.

 

[RalphLambrecht]

Hey, cool test, and good job of it!

If I may, I would hazard a guess that most of the effect is due to a slight dilution of the developer as a result of the water being carried into the developer by the wet film. But, just a guess - maybe or maybe not.

If you should ever want to investigate this idea it's possible to estimate the carryover by weighing a piece of scrap film when dry, then again when wet. Water weighs roughly 1 gram per milliliter as I recall. (Or, if you're using film on reels in a tank, there's probably also residual water in the tank/reels. )

FWIW if someone wanted to use a prewash and NOT dilute the developer, I'd guess it would be possible to deliberately over-concentrate the developer during mixing, just enough to counteract the amount of carried-over water per the volume of developer used.

Thanks for posting your test!

It's not due to the developer's dilution. The prewash water has already entered the emulsion, making it harder for the developer to get into the emulsion due to swelling, which impairs development.

 

[Mr Bill]

It's not due to the developer's dilution. The prewash water has already entered the emulsion, making it harder for the developer to get into the emulsion due to swelling, which impairs development.

Hi, I believe it is, more than likely, mostly due to the dilution.

FWIW I have pretty extensive experience in large lab processing systems, although mainly in color. I spent years as the QC manager, with 5 or 6 full time employees, including a chemist and a decently equipped chem lab. I know from experience that if a C-41 (color film) developer has a replenishment error of about 10% this is enough to move the "control plots" from near-center to near the "action limit" specs. Meaning still within spec, but recommended to take corrective actions. I would judge such density shifts to be roughly in the same range as ic-racer has observed.

Now, I have no actual experience with the process configuration ic-racer is working with, nor have I ever investigated the effect of prewashing (out of about ten commercial processes I've worked with, NONE have recommended a prewash). So I am strictly guessing on this, but I do think that it is very plausible that the 10% (more or less) dilution is the main culprit here.

One last note... the sensitometric effects of a diluted developer seem to significantly depend on how sensitive the developing agent is to development byproducts. So the results may vary, depending...

 

[MARTIE]

I'm pleased this topic has been brought up because I've noticed a visible difference between films with and without a pre-wash.
All pre-washed films have lower density and contrast by comparison.
So this thread all makes sense.

Can anyone calculate a time compensation for the drop in development activity?

By visual inspection alone, I'm guessing it will be closer to 20% rather than 10%. I will definitely be giving it a try away. So, thank you.

 

[RalphLambrecht]

Hi, I believe it is, more than likely, mostly due to the dilution.

FWIW I have pretty extensive experience in large lab processing systems, although mainly in color. I spent years as the QC manager, with 5 or 6 full time employees, including a chemist and a decently equipped chem lab. I know from experience that if a C-41 (color film) developer has a replenishment error of about 10% this is enough to move the "control plots" from near-center to near the "action limit" specs. Meaning still within spec, but recommended to take corrective actions. I would judge such density shifts to be roughly in the same range as ic-racer has observed.

Now, I have no actual experience with the process configuration ic-racer is working with, nor have I ever investigated the effect of prewashing (out of about ten commercial processes I've worked with, NONE have recommended a prewash). So I am strictly guessing on this, but I do think that it is very plausible that the 10% (more or less) dilution is the main culprit here.

One last note... the sensitometric effects of a diluted developer seem to significantly depend on how sensitive the developing agent is to development byproducts. So the results may vary, depending...

The effect of prewashing is not being questioned. The question is: What is the cause of decreased development after prewash? Is it because the minimal amount of residual water dilutes the developer, or is it because the prewash makes it harder for the developer to penetrate the emulsion? It's likely a bit of both, but I wanted to point out that there is more than just implee dilution going on. AFAIK, PE pointed this out on APUG years ago, and I'll check what Grant Haist wrote about it in 'Modern Photographic Processing'.