water filtration for PMK Pyro

[ward]

I have been reading the Book of Pyro and am getting ready to start

ordering chemicals. I have a plumbing network in my darkroom for

moving water to the various points, but it is not filtered. I have

considered an in-line filter, but Hutchings generally refers to

distilled water.

 

Are in-line filters enough? What should I look for in a filter

system? Any specific recommendations? Is water purity more of an

issue at certain parts of the process?

 

Thanks all!

 

--ward

[jorge_gasteazoro4]

I really would not recommend a filter only for PMK. If you water is very hard, an alkaline media will elute carbon dioxide and leave you with Calcium hydroxide, making the developer more active. This might sound like a good thing but if the hardness is not constant, which it hardly is, then you would have variable results. You also have the danger of scaling, precitpitation, etc etc. It is better to use destilled or deionized water. It is so cheap that for a few cents you are insuring your film processing.

[bob_finley]

I have a filter in line after the hot/cold mixing valve for washing as I have old galvanized plumbing and get the occasional particle in wash water without it. But I don't use it for mixed chemicals or final film wash even though we have very pure and very soft water from tap.

 

I use deionized water for all mixed chemicals as it is cheap insurance. You can get 5 gallon containers with spigot almost anywhere and fill them even at the grocery store. Five gallons of developer/fix/stop etc. will go a long way in a home darkroom and cost you as little as $0.25 per gallon.

[ward]

And then do you wash in straight tap water?

[doremus_scudder1]

Ward,

 

The problem with tap water and PMK is not so much the particulate content (though a 5-mil in-line filter is cheap and keeps the crud off of your film in the wash!), but the varying hardness (read calcium carbonate content) of the water, which can affect the activity of the developer. PMK is especially sensitive to carbonate levels and, therefore, development activity can vary greatly depending on how hard your water is.

 

I use PMK very often and develop negatives in two places: my residence in Southern Oregon and my apartment in Vienna, Austria. A little research showed that the hardness of the water in the two places varies little, but is different from place to place. Therefore, I have two sets of developing times for PMK, one for Oregon, one for Vienna, that are a bit more than 10% different. If you live in an area where the hardness of the water varies with the seasons, i.e. the water source is not exactly the same year-round, I would recommend using deionized or distilled water to mix your developer. This guarantees consistancy. By the way, distilled water for the final rinse in hard water areas is a must to elinate scale formation on the negs.

 

Hope this helps, ;^D)