Some darkroom questions

RalphLambrecht · Sep 4, 2009

Tom Kershaw said:
Ralph,

Is the graph presented here in 'Way Beyond Monochrome' first edition? I don't recall seeing it in the book.

Tom

It will be in the 2nd edition. remember, the 2nd edition has 560 pages. It's has quite a bit more content than the 1st.

RalphLambrecht · Sep 4, 2009

nworth said:
...2. There are a lot of ways to wash prints. Running water is usually the most convenient, but a series of rinses, allowing the paper to soak a minute or so in each one, also works just fine. RC paper washes out quite quickly. Most texts recommend 20 minutes in running water for batches, but it depends a bit on temperature, water flow, agitation, and a bunch of other things. I use an archival print washer, and I generally wash the prints for a half an hour in summer and up to an hour in the winter when the water is cold. This is condiered to be a bit long for RC paper, but I haven't had any problem with the paper coming apart at the edges...

3. ... Print development goes pretty well to completion, and minor changes will usually be wiped out during the process...

I agree with the erased portion of your reply, but...

Wow, what a waste of water! I've never seen a text recommending a 20-minute wash for RC paper. Actually, you are not doing the planet, your pocket or the print a favor. Minute amounts of residual fixer are good for your print. You don't want to wash everything out. That's why hypo-eliminators are not recommended anymore. Most texts recommend a 2-4 minute wash for RC and discourage hypo-clear (which I don't mind), but a quick and short sulfide toner does wonders for print longevity. Where did you get these excessive washing times from? They are good instructions for washing FB prints but not for RC.

To the myth of developing to completion, I added a chart earlier in the thread.

nworth · Sep 5, 2009

RalphLambrecht said:
I agree with the erased portion of your reply, but...

Wow, what a waste of water! I've never seen a text recommending a 20-minute wash for RC paper. Actually, you are not doing the planet, your pocket or the print a favor. Minute amounts of residual fixer are good for your print. You don't want to wash everything out. That's why hypo-eliminators are not recommended anymore. Most texts recommend a 2-4 minute wash for RC and discourage hypo-clear (which I don't mind), but a quick and short sulfide toner does wonders for print longevity. Where did you get these excessive washing times from? They are good instructions for washing FB prints but not for RC.

To the myth of developing to completion, I added a chart earlier in the thread.

I beg to differ, but only a little bit. A lot depends on the equipment. For RC prints you need at least two full changes of water, and the minimum recommended time at 21C is about 4 minutes. There are some excellent, sheet at a time, tray based washers that will do that. The texts recommend equipment that provides a full change of water every 5 minutes or less and at least 4 changes for untreated RC prints, 12 for untreated fiber prints. My equipment has a slower flow rate and I use rather cold water, which accounts for my longer wash times. With RC paper, water at 21C, and the recommended flow rate, 20 minutes is reasonable, but 15 will probably do OK.

RalphLambrecht · Sep 5, 2009

nworth said:
I beg to differ, but only a little bit. A lot depends on the equipment. For RC prints you need at least two full changes of water, and the minimum recommended time at 21C is about 4 minutes. There are some excellent, sheet at a time, tray based washers that will do that. The texts recommend equipment that provides a full change of water every 5 minutes or less and at least 4 changes for untreated RC prints, 12 for untreated fiber prints. My equipment has a slower flow rate and I use rather cold water, which accounts for my longer wash times. With RC paper, water at 21C, and the recommended flow rate, 20 minutes is reasonable, but 15 will probably do OK.

I see what you mean. Wash RC at slow flow rates in a so-called archival washer, like FB, and be done with it. I need to think about this. You may have a point if the paper can handle it.

dancqu · Sep 5, 2009

RalphLambrecht said:
Wow, what a waste of water!

I read posts that leave me in wonder of the huge amounts
of water wasted down the drain. I quote Fred Picker with
whom I am in complete agreement.

"No running water, no agitation! Archival washing requires
time, clean water, and print separation."

He has in mind the vertical slot washer with print separation
but without provision for running water. At most two fillings
are required. For myself I use a horizontal version. Prints
are placed in a wash tray where they alternate with
a separator fabric. A second tray allows for
transfers.

So, do not agitate. Keep the prints separated. Allow time
for the chemistry to diffuse outwardly from the prints.
Very little water is needed. Dan

RalphLambrecht · Sep 5, 2009

dancqu said:
I read posts that leave me in wonder of the huge amounts
of water wasted down the drain. I quote Fred Picker with
whom I am in complete agreement.

"No running water, no agitation! Archival washing requires
time, clean water, and print separation."

He has in mind the vertical slot washer with print separation
but without provision for running water. At most two fillings
are required. For myself I use a horizontal version. Prints
are placed in a wash tray where they alternate with
a separator fabric. A second tray allows for
transfers.

So, do not agitate. Keep the prints separated. Allow time
for the chemistry to diffuse outwardly from the prints.
Very little water is needed. Dan

Indeed, the process of print washing is a combination of displacement and diffusion. Just prior to the wash, a relatively large amount of excess fixer is gently clinging to the print through surface adhesion. An initial, brief but rapid, rinse in water quickly displaces this excess fixer, simply washing it off the surface. However, there is still plenty of thiosulfate left in the print, and this is a bit harder to get rid of. It has been deeply absorbed by the emulsion and saturates the print fibers. The remaining thiosulfate can only be removed by the process of diffusion.
As long as there is a difference in thiosulfate concentration between the print and the wash water, thiosulfate will diffuse from the print into the water. This gradually reduces the thiosulfate concentration in the print and increases it in the wash water. Diffusion continues until both are of the same concentration and an equilibrium is reached, at which point, no further diffusion takes place. Replacing the saturated wash water entirely with fresh water repeats the process, and a new equilibrium at a lower residual thiosulfate level is obtained. However, diffusion is an exponential process that decreases geometrically with time. This means that the rate of diffusion slows down rapidly towards the equilibrium. Print washing is quicker if the wash water is not entirely replaced in certain intervals, but slowly displaced with a constant flow of fresh water across the print surfaces, keeping the concentration difference, and therefore the rate of diffusion, at a maximum during the entire wash.

wogster · Sep 6, 2009

RalphLambrecht said:
Indeed, the process of print washing is a combination of displacement and diffusion. Just prior to the wash, a relatively large amount of excess fixer is gently clinging to the print through surface adhesion. An initial, brief but rapid, rinse in water quickly displaces this excess fixer, simply washing it off the surface. However, there is still plenty of thiosulfate left in the print, and this is a bit harder to get rid of. It has been deeply absorbed by the emulsion and saturates the print fibers. The remaining thiosulfate can only be removed by the process of diffusion.
As long as there is a difference in thiosulfate concentration between the print and the wash water, thiosulfate will diffuse from the print into the water. This gradually reduces the thiosulfate concentration in the print and increases it in the wash water. Diffusion continues until both are of the same concentration and an equilibrium is reached, at which point, no further diffusion takes place. Replacing the saturated wash water entirely with fresh water repeats the process, and a new equilibrium at a lower residual thiosulfate level is obtained. However, diffusion is an exponential process that decreases geometrically with time. This means that the rate of diffusion slows down rapidly towards the equilibrium. Print washing is quicker if the wash water is not entirely replaced in certain intervals, but slowly displaced with a constant flow of fresh water across the print surfaces, keeping the concentration difference, and therefore the rate of diffusion, at a maximum during the entire wash.

One of the issues is the with RC papers any thiosulphate in the paper, from cut edges, etc doesn't matter, because the resin coating is a barrier between it and the emulsion, there may not be a lot of thiosulphate in a thin emulsion, so it may not take a lot of washing to get it out. These days when in many places water is in short supply, which makes it relatively expensive, washing prints for hours in fresh water seems kind of silly. One wonders if the Ilford method of washing film, which uses relatively little water to archival standards, is good enough for negatives, why we need to wash RC prints for hours in running water to achieve pretty much the same thing.

dancqu · Sep 6, 2009

WE?

wogster said:
... why we need to wash RC prints for hours in running
water to achieve pretty much the same thing.

Don't include me. Two minutes according to Ilford.

When I was using RC I'd give a print out of the fix three
tray rinses, of 1, 2, and 3 minutes using a minimum of
water. Were I to work with RC again I'd cut that to
three 1 minute rinses or maybe a 1 and a 2
minute. I was overdoing it. Dan

Some darkroom questions

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