Prolonged soak in demi. water for film
Just like others, I have at times struggled with drying marks on my film. While using wetting agent, and shortly dipping the film in demineralized water, still sometimes drying marks were left behind.
Now I have recently decided to leave out the wetting agent altogether and just do a last but prolonged soak of the developed film in demineralized water (10-15 minutes).
The films comes out very clean after drying, even when droplets were present when hanging them for drying. It seems to go better than before.
Are there any other people simply using a prolonged soak in demineralized water as the last bath for developed film? What are your experiences? Any possible cons to this approach?
Last edited by Marco B; 07-24-2009 at 09:29 AM. Click to view previous post history.
"The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true.
" - William M. Ivins Jr.
"I don't know, maybe we should disinvent color, and we could just shoot Black & White.
" - David Burnett in 1978
"Analog is chemistry + physics, digital is physics + math, which ones did you like most?
personally, i just use EK photo-flo with distilled water for a minute or so before hanging up to dry. i dry at room temperature, no heater, and i try to hang the negs in a place where there is little dust. some hang their negs in the shower after running it with HOT water for a minute or so, the steam generated helps to keep the dust down.
What is demineralized water?
I use distilled water and photo-flo, and pour alcohol on top. The alcohol gets rid of any bubbles that might stick to the film, and i'd like to think it forms a layer that coats the film as i pull it out causing it to dry faster. Film seems to dry faster now than when i just used water and photo-flo, but i've never timed it.
Long soak in distilled water is actually to avoid because it will soften the emulsion too much. Try a fresher wetting agent, when old it leaves residues even used much more diluited (at least I've solved my problem this way).
Plus current wetting agents contain sequestrants to cope with hard waters.
Adjust the amount of wetting agent to suit the "demineralised" water your using... relatively small differences in pH can affect surface tension. Also, as with any chemical, wetting agent can vary especially from manufacturer to manufacturer. When I was still processing my own film I generally needed to use a bit more than they recommended. I used Photo-Flo and commercially distilled water.
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Water is distilled to demineralize it.
Originally Posted by c.w.
^^^ Some providers claim reverse osmosis filtered water is "demineralized". They don't claim "all minerals removed" though most of the minerals are gone. At any rate even the best filtered water behaves a bit differently than distilled.
A prolonged soak isn't necessary IMO. I use filtered well water with a few drops of dish washing detergent as a surfactant and have not experienced any drying marks.
A few passes through it are enough then hang to dry.
It may be your wash is not any too complete. The long
Originally Posted by Marco B
soak allows a complete diffusion outward of chemistry
left in and on the emulsion.
I use a protracted Ilford wash sequence and afterward
a short soak in half strength PhotoFlo; all with distilled
water. After hanging an eight blade film squeegee rids
the film of all surface water. Dan
You are correct.
Originally Posted by Mike1234
Richard Knoppow posted the following text on a different forum a few years back. I believe it gives a very good description of deionized, distilled and demineralized water, and their differences.
'The theoritical pH of pure water is about 7.0 but it is extremely hard to measure due to it poor buffering capacity. You just have to expose it to air and the pH will change!
Reverse Osmosis As the name implies, it is the reverse of osmosis. If you separate pure water and less pure water with a semipermeable membrane, the water from the pure water side will flow into the less pure water, just like water flowing downhill. If you apply pressure to the less pure water, water will flow in the reverse direction and that is how you get purer water by reverse osmosis. It is the least pure water of the three.
Distilled water By boiling water it forms steam which condenses into distilled water. It is still not very pure because some of the trace metals will be carried over with the steam. To get really pure water you redistilled the distilled water again to get double distilled water. In reality we need all glass utensils, reflux condensers, etc. It is a more complicated and expensive process than the name implies. Commercial distilled water is not very pure because it is just a steam distillate!
Deionised water It is common to put a reverse osmosis unit or a steam distilling unit in front of a mixed bed deionised unit. Basically tap water contains plentry of M+ and M-, the common ones are Ca2+, PO4--, Na+ and Cl- to name two, most of the problem in photographic process is caused by Ca2+. The purer the water the less M+ and M-. If one pass water through a mixed bed deioniser, the M+ and M- is captured by the resin and only water passed through.
Without going into too much details, generally speaking if properly done, deionised water is purer than distilled water which is much purer than water obtained by reverse osmosis. To put it bluntly unless one have a very 'hard water supply' it is unlikely that the water used with affect the photographic processes. One easy way out of problem with 'hard water' is to collect rainwater and use it instead.'