My argument is not whether Permawash is a good product. I'm sure enough that it is that I have used Permawash for my own film and paper. My argument is solely whether I trust their verbiage and instructions, for anything better than momentary print survival. I use a higher concentration, longer rinse, longer bathing in wash aid and longer wash times. I use the conservative times that Kodak suggests. I'd rather be safe than sorry.
I don't know how this discussion driftet to one product, I started reading the thread, and skipped to the end....
Being a chem. engineer, and having worked years in a laboratory I can offer some advice. In a standard Paterson tank for two films, one need no more than 4 - 5 liters of water.
There are two principles at work here, dilution and diffusion.
At first one simply dilutes the fluid, this works fast, just a few seconds, but later in the process what is needed is getting the fixer salt molecules out of the emulsion, that is diffusion and takes minutes.
One also needs to take into account the rest of the last bath that remains inside the tank, every time one drains.
Dilution works all the way during the process and is what needs to be taken into account, as soon as the molecules have diffused out from film and into solution.
All this is standard operating procedure in all classical analysis work in any laboratory.
The calculation is like this : Drain fixer 600ml , in the tank remains 30ml that adheres to the tank insides, spiral, film and so on. Dilution is 30/600 = 1/20 and remains constant for every change of water.
repeated changes works this way 1/20 * 1/20 *1/20 = 0.000125 in other words concentration is reduced to 0,0125% of the original fixer bath.
In 6 changes one is down to a concentration of 0,000 000 015 or 0,015 millionth of the start.
If the procedure is something like this :
Empty fixer, fill with water and shake for 5 seconds, drain.
Repeat, shake double the time every time until this is repeated 7 times
Time increases like this : 5 - 10 - 20 - 40 - 80 - 160 - 320 seconds, no need to shake all the time but diffusion takes more and more time during the porocedure.
Last cycle will require some 5 minutes stand time, shake at first and a few times during the 10 minutes.
Concentration will now be down to 0,000 000 000 781 or a billionth of the start concentration.
One has used just 4 liters of H2O, compared to about 120 liters for an hours rinse in running water, and as any chem. engineer will tell you, even after an hour of running water the concentration will NOT be lower than after 7 changes of water.
The whole thing will take about 12 minutes, one has to work a little, the film will be perfectly rinsed and easily last 50 years as has mine since 1962, I have used this procedure for ever, except for a few years when I got a Paterson "tube", I note that there are a couple of spots on a few of the films from those years (the lazy years...) before and after they are spotless.
BTW I learned this not in school but from a german in a book : Hans Windish "Die neue Foto-Schule I, die Technik" apparently water was scarce in western germany after WW2!! The book is still recommended if it can be found, I have my copy.
Closing I will just note that archival copies on paper can be treated after similar principles. Using a couple of baths, draining the previous water out and changing 8 to 10 times should get prints that will last forever.
A method that I have used for many, many years is to use a cylindrical plastic conainer large enough to hold several reels. In the bottom are drilled a few very small holes. I insert the reels and fill the container once and then pour out the water to remove any fixer trapped in the reels. Then I adjust the water flow so that the container remains filled with water and little spills over. Clean water enters at the top and water and fixer exits the bottom. The size and number of holes are adjusted so that once filled the container will drain in approximately 1 minute when no additional water is added. I leave the container under the tap for 20 minutes. Since the flow rate is quit small I feel this method conserves water while providing good washing. I have negatives that are 50 years old that show no problems from residual fixer. The diameter of the container should be small enough so that the reels do not move around but remain on top of each other.
Gerald this way, slow running water will give less effective wash than 5 changes of water and about 1000 times less effective than 7 changes. I'm not saying you get bad results, but you waste both time and water.....
Please look at the math I have presented earlier in this and other threads, which was first shown by Mason in his text in the chapter on washing. The basis for it is dC/dT (Change in Concentration in the film or paper vs Time) and the only way to prove what is good is to test with a hypo retention kit and a silver retention kit. Mason and others do show that running water is better than standing water, and agitation is better than no agitation.
Running water gives you a GRADIENT, it i much like recharging batteries, where the curve flattens with time, ie washing gets less and less effective.
Dumping everything and extending time slightly with each water saves time, saves WATER and is the only way such things are done among professional chemists, Mason and others nonwithstanding. In classic chemical analysis, with a rotating gizmo, 3 changes of water is generally held to be enough....
I used to do this for a living, in part of my professional life.
Mason, P 204 gives the equation as:
dX/dT = K[(a - x) - w]
Where w = conc of hypo in the water adjacent to the emulsion, K = a constant based on conditions under test (thickness, hypo type, silver concentration, swell, etc), a= the initial concentration of the hypo, and x is the loss after time t.
This equation is most efficient with running water as you reach the minimum desired level of hypo. With changes of water you get concrete downward steps that approach this value, but in a less efficient manner.
If done correctly, they can both work, but usually the method of changing water is misused and Mason, who originally advocated this method, changed his opinion in later years (and in this text) to that of recommending running water with agitation.
Of course, re-presenting this argument here opens a years old debate on APUG here and on Photo Net on this subject.
I suggest you use what works for you but test for residual hypo and silver to insure proper lab procedure.
At the same time, there are other ways to improved hypo and silver removal if one is interested, but none of them are perfect either as they use additional chemicals to promote silver and hypo removal by a variety of methods.
There is no significant problem with the slight amount of hypo produced and the slight amount of silver produced in any method of wash. In fact, the multiple wash method produces, on average, exactly the same amount of hypo and silver in the waste water as any other method.
So the consumption of water may differ, but the effluent is "contaminated" by the same amount in both cases. Your film is probably better off using the continuous wash method however.
At present, I am working on ways to reduce the amount of wash needed for any film or paper. I find that the cost is quite considerable to the consumer but depending on water resources, some may be willing to pay that price.
Mason's work (at Ilford) complimented G.I.P. Levenson's (at Kodak, Harrow) and it's no co-incidence that Levenson was the editor working with Mason on his book.
The years old extremely heated debate on Photo.net etc was based on incorrect assumptions, Levenson's work at Kodak was on washing after Sodium Thiosulphate based fixers often with a hardener, while the later Ilford wash technique is based on Ammonium Thiosulpahte based fixers (Hypam) with no hardener. A fact conveniently over looked by both sides until Roger Hicks pointed it out.