Theory also breaks down slightly because hard water washes films & papers more effectively than soft water (or de-ionised/distilled water).
So that's another reason why Ron's comments are important here.
Originally Posted by Photo Engineer
I would like to add:
Depending on the ions, some hard waters can slow down washing. This is due to the decrease in swell caused by Sulfates, and the change in swell due to the pH of some water supplies. For example, water with a lot of Calcium Sulfate or Aluminum Sulfate, which would be slightly acidic (beyond the norm introduced by Carbonate perhaps), would sharply decrease swell.
In addition, Calcium ions tend to slow fixing and washing due to the nature of their effects on hypo.
This is why I suggest running tests with your local water supply, as it can have a major impact on the final times of fix and wash.
You relly did grasp this Fabrizio!
Originally Posted by Diapositivo
I have nothing further to add,my post was NOT an attack an Greg, nor on PE, it was just to highlight that the testing method will measure down to COMMERCIALLY sufficient levels, beyond that it simply says nothing meaningful.
I can live with that. because I always washed to archival levels anyway, not because I'm overly concerned with that, but because water is cheap where I live, and because I can.
I used to use running tap water, but think that is a nuisance around HERE, this being Norway, we have very cold tap water (no ice needed when I enjoy my oirsih whiskey!!).
Since I'm more concerned with emulsion reticulation than remaining thiosulphates, I decided to go to slush-and-discard watering, I can conntrol water temperature within 1 degree Celcius that way.
I did a little research, dug out long forgotten school training, my chemistry class, I'm an old chemical engineer. So I discovered that this watering business was in line with my classical formal chemistry education, and EUREKA, the good old Ilford system was better from bolth a teoretical and practical point of view. For ME.
You can do what you like, as long as the film spend enough time in water and you use enough of it or changes it enough, you will be good. You will reach commercial levels easily and fast, archival levels with just a little more work or time.
This is really no big deal, its almost infathomable that anyone can spend so much time debating such a simple issue,m and make something so simple look so hard.
Have a nice time all of you, but make damn sure you spend a lot more time photograping, than debating issues that was debated to death more than a century ago.
Out of Curiosity. When I worked with Microfilm, We were always to ask for a "Methylene Blue" test that said the film was washed "sufficiently". I only saw a consultant once with a bunch of dropper bottles and a penchant for only working when he was alone.
What is the difference between the MB test and the Silver Nitrate test that we are discussing here. Would sending some of the Doubters off to repeat this test sequence with Methylene Blue help the cause?
I still live just beyond the fringe in Stittsville
"There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).
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You see why this method is not just for anyone? Also, there are standards, as I have stated before, for retained HQ and Metol, but there is no good test for them either.
Anyone interested in my test setup, here are a couple of images. One is of my flow meter and homemade stand. The plug on top is there until my screw in thermometer arrives later this week. The other picture is of the test to determine the necessary flow rate by adding food coloring to the water in the tank, and I only had green available. The thing entering the tank is a stainless steel tube small enough to go through the core of a Hewes reel. By adding a rubber stopper on the end, I can plug up a plastic tank for forced washing, as well.
Very nice Greg. Well done.
Pretty mundane stuff for anyone trained and with experience working in a modern lab.
Originally Posted by cowanw
In my day we did this manually of course, measuring with precipitates and such. You would spend a *lot* longer analysing anything than just washing a little longer.....
And that link to a 124$ or was it £, for a PDF-file describing the process was hillarious, some are prepared to being shafted or to quote JP Barnum *there's one sucker born every minute*!!