Indicator stop bath failuregreenspun.com : LUSENET : Large format photography : One Thread
Sometime ago, I regaled this forum of a problem in my darkroom to wit; hypo that turned blue and lost it's potency. Nobody had a real good answer. Well, I got one now and it does not lead to a tranquil mind.
The protocol; Printing trip snapshots from Ireland(not LF, sorry about that) onto 8x10 single weight paper, two negs on some, one on others, mounted back to back, wide borders allowing india ink annotation, to be passed around to the awed multitudes (my relatives of which there are a large number) while we talk about our trip. We are not talking archival here.
Developer: 36 oz Dektol: 1+2 water Stop: 32 oz Kodak Indicator Fix: Pure hypo Normally, I use Kodak Fixer for this, but had none mixed, hypo was.
I was printing along when I noticed that my stop, saved from a previous short session, was getting darker, no blue, a deeper yellow. I always change at that point, so I did. I was then astounded to see the hypo turn blue. Hmmm! I threw everything out and left quietly, not looking back.
In the middle of the night, Fred Picker's voice came out and said: "Test!"
After completing the run of prints the next day;
The stop had 5 single weight sheets through it. It took about 4.5 oz more developer to get it to the color at which I normally change.
The hypo had 5 single weight sheets through it. It took less than 0.2 oz of developer to develop a blue tint.
Conclusion: The indicator is worthless in the stop. I had always suspected this so I never ran it to purple. Now I find it is REALLY worthless. (Unfortunately, I forgot to continue on with the developer/stop test to see what it took to turn it blue.)
Hypo apparently has no buffering against alkaline developer that gets through the stop. I would expect that Kodak Fixer would. That is probably why I have had no visible problems in "production" printing because I usually use Kodak Fixer.
I usually reserve hypo for prints that are going to be toned, spotted and (I hope ) sold. If I am using a 'known' neg, I rarely print more than five 11x14's total including trials, in one session and I use all fresh chemicals so I hope there are no photos out there fading away.
Vestal says 20 prints/qt is stop capacity. The Kodak Darkroom Guide says substantially the same thing.
RJ Harris determined that a double weight print drained at least 15 seconds until the drops are 1 sec apart, carries 0.2oz of developer into the stop. As I didn't wait that long, I guess my single weights were carrying about the same amount. I was probably around 20-25 photos when I spotted the problem, so it occured before that. I think the 20 print/qt is optimistic. Better back off to 15 WELL-DRAINED 8x10 prints.
For 'fine' printing, I usually replace my developer and hypo at 10 8x10's so the stop now goes with the other two. I refixed the photos of the day before
I thought I'd tell you folks in case you had thought that you had finally found inner peace in your dark room.
-- Richard Trochllil (email@example.com), November 21, 2001
You RE-USE your stop bath? Well, what do you expect?
You really don't need an indicator to tell when the stop's used up. It loses its slightly 'sticky' feel and becomes slimy to the touch. At which point you sling it, and make up some fresh 2% acetic acid or metabisulphite solution.
-- Pete Andrews (firstname.lastname@example.org), November 21, 2001.
I am a simple soul and an amateur chemist- well trained but lapsed. When the indicator stop bath loses it's vinegar smell, or starts turning dark, I splash some ordinary distilled vinegar into it until it turns lighter yellow and I can smell the vinegar again. I keep using the same replenished bath until the bottle fills up, then dump some and refill with cheap Food Grade 5% Acetic Acid; i.e. vinegar.
I too wake up in the middle of the night too the imprecations and dire warnings of Fred Picker, but realize he gets at least $150 per print and can afford fresh chemicals every session.
There are many printers who use a simple water bath before fixing. Most proper fix baths DO have buffers included, just for that reason. Pure Hypo was replaced with a proper compounded fix bath over a hundred years ago just because of that. It is OK for toning purposes, but only after using a proper fix bath.
-- RICHARD ILOMAKI (email@example.com), November 21, 2001.
I suspect that your plain hypo bath is turning blue due to the carry- over of the indicator in your stop bath that turns blue in a more alkaline environment. Since you used plain hypo, which has a rather neutral pH, the carried-over indicator would naturally turn blue. This is its job. If your stop were the same pH as the plain hypo bath, it would also be blue and not function as intended. However, just because you have dyed your fix a nice shade of blue does not mean that it is exhausted. It will still fix as many prints as before. An acid fixer would, of course, not turn blue. It would simply take on a slightly yellowish tinge from the carried-over indicator (I'm sure you have noticed this in the past). This carry- over is normal and does not affect the activity of the fixer. Also, your stop bath is working just fine if it has not started to darken or turn blue. The exact pH of the stop is not as critical as some would lead you to believe. Running water works well, albeit more slowly, as a stop and it is of neutral pH. The main thing is to arrest the activity of the developer. So long as the pH is at a point where there is negligible developer activity this is accomplished. There are other factors that affect the useful life of plain hypo fixers, but in your situation things like oxidation and sulfur precipitation do not seem to be important determiners. As for re- using stop: go right ahead, just toss it before it loses its acidity. Discarding it before, or just as the indicator starts to change color, as you do, insures that the prints are adequately stopped and gives you a nice "fudge factor". Hope this helps clear things up (NPI). ;^D)
-- Doremus Scudder (ScudderLandreth@compuserve.com), November 22, 2001.
Hmmm! My hypo did not turn blue UNTIL I started with the new fresh stop. That led me to believe that developer had gotten into it, past the old stop that had not turned blue. Otherwise, why does hypo not turn blue with the first print? All of which leads me to believe that the indicator stop not indicating can still let alkaline prints get by.
And once developer gets into pure hypo, I think it loses its potency fast. Lootens kind of implies that. However, I had no way of testing that, so that is just a surmise.
I have been a bottler from way back, but now even indicator stop is suspect for me.
As I said, none of this leads to a tranquil mind.
-- Richard C. Trochlil (firstname.lastname@example.org), November 22, 2001.