Capacity of Citric Acid Stop?

[tgtaylor]

Anyone have an idea of the number of 8x10 prints per liter a 1.5% citric acid stop bath will process? Dektol is the developer.

Thomas

[Jim Noel]

It is so cheap to mix, why take a chance. Just mix fresh for each 4 hour session.

[tgtaylor]

It is so cheap to mix, why take a chance. Just mix fresh for each 4 hour session.

Thanks Jim.

Except for Perma Wash, Photo-Flo, and C-41 Stablizer which I use to near capacity I toss all other chemistry after each session. The capacity of the Dektol is 32 8x10 prints per liter of working strength developer and I'm wondering if the capacity of the citric acid stop would be similar if not the same. It's much easier to count print to know when you are nearing solution capacity.

Thomas

[cyrus]

Thanks Jim.

Except for Perma Wash, Photo-Flo, and C-41 Stablizer which I use to near capacity I toss all other chemistry after each session. The capacity of the Dektol is 32 8x10 prints per liter of working strength developer and I'm wondering if the capacity of the citric acid stop would be similar if not the same. It's much easier to count print to know when you are nearing solution capacity.

Thomas

I don't know the capacity and I'm not sure that many people really bother with that when it comes to using stop solution.
I suppose one can test the stop solution using a ph strip to make sure it is still mildly acidic.

[Ken Lee]

"Except for Perma Wash..."

If you use a non-alkaline fixer, you can easily make your own washing aid (http://www.digitaltruth.com/data/washaid.php): just use a teaspoon of Sodium Sulfite per liter of water, and toss it when you are done.

If you use an alkaline fixer, you don't need a washing aid.

According to Anchell and Troop, in The Film Developing Cookbook (http://www.amazon.com/Film-Developing-Cookbook-Darkroom-Vol/dp/0240802772), Alkaline Fixers have the following advantages over more traditional Acidic formulas:

Less danger of over-fixing
Shorter washing times
More archival
Greater capacity
More stable
Can be formulated to have low odor.

[tgtaylor]

Thanks for the tip Ken. Perma Wash is pretty expensive stuff and I haven't thought of mixing it myself until now. A quick inventory shows that I have sodium sulfite in stock as well as sodium bisulfite which, according to the 12th edition of Harleys Condensed Chemical Dictionary (1987), "its properties and uses are practically identical" with sodium metabisulfite. But the latter is inexpensive so I'll add it to my shopping list.

I do use TF-5 but also use HCA (which I mix) and Perma Wash for "insurance."

Thomas

[cowanw]

I suspect it depends on how long you drain your developer off.

[JBAphoto]

Squeeky test - grip the edge of a test strip and rub between your finger and thumb, if it does not "squeek" discard your stop bath

[Doremus Scudder]

As for the stop bath, the "squeaky test" described above is a pretty good indicator of exhaustion; if the stop doesn't remove the slipperiness of the developer, then it's exhausted.

Also, my citric acid stop form Amalco has an indicator in it, like the good old Kodak Indicator Stop. So does the citric acid stop from Fotospeed. You could also just add the bromocresol to the stop yourself and make your own indicator stop.

Don't keep citric acid stop baths in working solution for a long time anyway. Because the acid is organic, it tends to grow mold and bacterial crud after a while. I use mine one-shot/one session. I usually mix at about half strength for film developing.

As for washing aids: you certainly don't need both HCA and Perma Wash. There is some doubt about whether Perma Wash really works anyway. Some swear by it, but a quick look at the contents and the dilution leads me to be skeptical...

At any rate, using HCA alone is more than enough. As mentioned above, you can mix your own easily. My recipe is one Tablespoon of sodium sulfite per liter plus a pinch of sodium metabisulfite.

If you want extra archival protection for your prints, then treat in a stabilizer like Sistan (there are a lot of knock-off products on the market now too) before drying.

Best,

Doremus

[Cor]

You can brew your own sotp bath:Add 400gr Citric Acid, Bromecresolgreen (indicator yellow to purple at around pH 6-7), and Methyl Parabene to prevent growth of slimy things in a final volume water. Dilute 1+19 and discard when blue/purple. Exact concentrations, except Citric acid are in my notes, not here right now.

Best,

Cor

[tgtaylor]

Thanks for the input everyone - good stuff!

My copy of Hawley's says the green version changes color (yellow to blue) over the pH range 3.8 - 5.4, and the purple version (yellow to purple) 5.2 - 6.8. Private citizens can purchase the green but not the purple which must be shipped to institutions. Anchell only gives the formula for the purple in The Darkroom Cookbook and right above it is a formula for Bisulfite Stop Bath. Probably the best choice would be to use the squeek test and the pH paper to determine the number of prints per liter.


Thomas

[Doremus Scudder]

... Probably the best choice would be to use the squeek test and the pH paper to determine the number of prints per liter.

The problem with trying to determine a "prints-per-liter" capacity for a stop bath is that its life depends on the alkalinity of the developer, the amount of developer carry-over when transferring prints, the hardness of the water it was mixed with, etc. That's why I like the indicator. Of course, I don't let my stop get totally purple; the minute I notice a bit of a change from bright yellow to greyish, then I toss it. The "squeaky test" is just about as accurate.

Keep in mind, that in printing, the function of the stop is not only to stop development (which can be accomplished in a fairly neutral pH), but also to keep the acid fix running well through its entire useful life.

Speaking of capacities, similar constraints apply to developer and fix, i.e., "prints-per-liter" capacities are simply approximations based on averages plus a safety factor. Develop a lot of prints with a lot of black area and the developer will die more quickly than if you had developed prints with large white areas; the opposite for fix :)

Best,

Doremus