Would you be so kind to give me (us) a hit whereabout I can reed some prove that I (we) shall not use the Ilford Method......
Everything is analog - even digital :D
L. F. A. Mason, "Photographic Processing Chemistry", Focal Press. Read the chapter on washing in which he shows the differential equation related to outward diffusion of hypo from film.
it seems clearly VERY sound to me - I don't see how you can go wrong - as long as you agitate (that's critical). Any level of knowledge in chemistry, physics and affiliated sciences really aren't going to be able to take the place of proper testing for residual hypo levels on the emulsion.
I'm really getting tired of this argument.
Diffusion is a continuous process and Mason shows that in his book. Others have too. If you don't wash in a continuously changing water supply, then hypo and other things build up and slow down the washing process.
Even with agitation there is a finite amount of exchange expressed as dc/dt or the change in concentration vs time within the film as a function of volume of water.
I have the book sitting right here next to me and I did when I answered the protestation in the last thread on this. Haist and others also disagree with washes that are not continuous.
Why take a chance?
Of course, you can do whatever you want to. After all, it might take 20 - 50 years to see if you have any problems so why worry.
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Just thought I'd check the Ilford method. It actually says 5, 10 and 20. When you compare it to the continuous flow method of a tube inserted to the bottom of a tank and the wash times in the older books on processing then it does seem to be very little water by comparison and of course the Ilford method isn't continously emptying the contents as the constant flow method is. However a change to process and much less water isn't necessarily per se a less efficient process.
PE. I confess to problems with technical explanations and I have read the APUG link provided but didn't find myself much the wiser or at least not as wise as I'd like to be.
I haven't got a copy of the LFA Mason book and I fear I am unlikely to be able to get one and I haven't seen the Kodak method so can I ask you:
1. What is the Kodak method
2. Does L.F.A. Mason say what the problem with the Ilford method is?
3. If so what does he say, in layman's terms, if possible
4. What modifications, if any, to the Ilford method are possible which help overcome its problems
I appreciate the answers to 2&3 may answer Q4 and if so ignore Q4.
The Ilford method seems to involve 35 vigorous agitations which seems to be quite a lot but only 3 dumps so I am assuming that the problem involves the number of dumps as I would have assumed that the nature of 35 inversions presents quite a force to remove fixer from the film but not getting rid of the fix-contaminated water continuously but swirling it around the film may be key to the problem identified by Mason or it may be that even 35 inversions are not enough to separate the fixer from the film.
However I am speculating now and I would do better to wait for your response
I've read the old posts and heard both arguments, and I personally use the Ilford method and then I let the film sit in a tank of running water for an extra 3-5 minutes while I prep other things, clean up, etc.
This is using Ilford Rapid Fixer. So no hardener. (Could this be part of the disagreement, some people using hardening fixers and some not?)
I do it to conserve water and save time.
The Kodak method uses continuous running water until the film passes 2 tests, namely the residual silver and residual hypo tests. Solutions for these can be purchased at most photo supply houses.
Mason effectively ignores the method that Ilford has posted on their web site, but he does say that one wash with a volume of X is 840 times more effective than 3 washes each one with 1/3 the volume of X, and therefore washing in continuously running water by the same analogy is infinitely more effective.
You see, the change in concentration of hypo in film depends on the concentration in the wash water and the time the film is in the water. If you don't maintain the concentration of hypo in the wash water at as close to zero as possible, then you cannot bring it to zero in the film.
Therefore, the only way to bring it to zero in the wash is by running the water all the time.
Mathematically this is: dx/dt = K[(a - x) - w] where
dx is the rate of change of hypo in the film
dt is the rate of change of time
K = a constant (depending on film, temperature, hardness etc)
a = initial amount of hypo in film
x = loss of hypo after unit time
w = amount of hypo in the wash water
The lower the value of w, the faster and better the wash is.
So, with a continuous wash, w = 0 (ideally) and is the fastest and best wash.
The method that he describes is a continuous wash of several tanks where fresh water enters the final wash, and then is circulated to the next from last and then second from last and etc until it overflows the first wash tank. During this period the film or paper is moved from the first (most contaminated) wash to the last through continuously running water.
This is the method that Kodak and Pako used in their processors.
The best method is to use running water for the time necessary to remove all residual chemistry to pass the test and it varies from film to film, paper to paper and from process chemistry type to type. I cannot give you an exact figure. You must test for the time yourself.
Dumps and inversions are NOT going to save you as the wash proceeds thusly. Lets say 50% of the hypo is removed in 10 mins. Then 50% remains. Then in the next dump, 50% of 50% is removed. In the next dump, 50% of 25% is removed. In continuously running water, the amount changes more rapidly and can approach zero more closely, as there is never any "w" left in the wash water.
PE makes perfect sense to me. Even in bathing ones self, if you sit in a bathtub full of less than clean water vs. the shower with always clean water.
Hey, maybe take the film or paper with you in the shower
It seems meaningless to even discuss this further academically - the only way you're going to prove whether the 'ilford method' works enough to give you a neg that contains a below-critical level of residual fixer is to do a rigorous test based on established standard target levels.