back dots on student negatives

[wcroninger]

<p>We are having a run of irregular black dots on all HP5 negatives developed by students in my intro to photography class. Student prints look like someone stood back and threw dust at the negative, which is what I first suspected until it began to show up on all their negatives. There is no pattern to the spots, they can appear within the image, between frames and within the sprocket hole areas. I discarded all developer and wetting agent last night then used distilled water to mix new. Same problem occurred. The fixer tested as good but I did notice quite a few "floaters" in the batch, so I am leaning towards this being the problem . Couple other possibilities that I want to ask the group about based on what I've read in various threads.<br>

1) Problem seems to have started after I loaded a new 100' roll of HP5 in the bulk loader, defective roll?<br>

2) The Fixer jug is old, residue?<br>

3) We use well water which occasionally has a very strong sulphur smell, bad enough that we have had to discard wetting agent.<br>

4) After developer, students wash for 30 seconds with running water. <br>

Looking at the negatives under a high power loupe the spots are black, irregularly shaped and appear to be "in" the film as opposed to on it.<br>

Any thoughts? Please feel free to point me at a thread that I might have missed.<br>

Thanks!</p>

[User_502260]

<p>Did you by any chance filter the water used to make up or dilute the developer with a charcoal type filter? These filters need to be rinsed well or they can throw off black particles. Do you re-use either the developer or the fixer? If so, you need to filter them through coffee filters to remove particles. </p>

[Craig_Cooper11664875449]

<p>Youre #2 is always my biggest headache with embedded crud on the negatives</p>

[peterbcarter]

<p>Ditto</p>

[nbg90455]

<p>Toss the fixer, and the fixer jug (unless you can get it sparkling clean)...</p>

[Mike Howard]

<p>Reusing fixer over and over without filtering leaves little particles of silver in it, which can cause the black specs you are getting. Try the coffee filter approach for pouring the fixer back into the bottle, this should help a great deal.</p>

[jpo3136b]

<p>How about fixer cross contamination with developer?</p>

<p>Sources could include some trace fixer crystal caked in the developing tank lid; it'd be not just a simple mix up; if it is cross contamination from between uses, then I'd say a preliminary rinse with water and fresh drying of the tank will get rid of this.</p>

[chris_waller]

<p>I'm also inclined to think that it's residue in the fixer. I filter mine through a coffee filter after every 10 films.</p>

[wcroninger]

<p>Thanks for all the replies, I am also leaning towards contaminated fixer. The jug has been around for a long time and is caked with dried fixer and ? on the outside. Who knows what is living inside! <br>

During the Fall & Spring semesters we have around 36 students continuously using the two labs so the comments regarding filtering fixer are very useful. I will look into that. John the cross contamination idea is a possibility had not previously considered. We use a 20L floating lid tank for negative developer and I had just cleaned that pretty throughly between students so think we are ok there. But that also makes me wonder about how well the students are cleaning up after themselves so check all the developing tanks. <br>

I think we need to "invest" in a competent work-study during the year and setup a regular and timely cleaning schedule. The "black-spots" are new but we have ongoing problems with heavy sulphur smell and water spotting of negatives. A bit more emphasis on cleaning could not hurt.<br>

One last question, any thoughts on how to clean a plexiglas or lexan archival washer? I drain and wipe it down regularly but we have a real issue with "mineral" deposits on the outside where water dries.</p>

[lex_jenkins]

<p>Ditto the fixer sludge. I usually decant my recycled fixer as sludge accumulates, but filtering would work too.</p>

<p>Your well water sulfur problem is very familiar. Up until 2005 or so I was in a rural home with limestone basin wells and had the same problem. Darned stuff can kill an electric hot water heater every few years even with a sacrificial anode. I used the well water only for washing my prints. I tried filtering the well water but it still caused problems with my negatives so I switched to distilled water for mixing my darkroom chemicals and washing my film. Helped minimize problems with spotting on my negatives.</p>

<p>Good luck with your students. The main challenge is getting them to cooperate with consistent, proven methods. They tend to either take shortcuts or want to try experimental processes they've read about online before they've grasped the basics.</p>

[jpo3136b]

<p>For cleaning off of those water spots, have you considered some calcium carbonate in the water? A little Oxy-Bleach to soften up the water. Maybe a tablespoon to 2 to 5 gallons?<br>

Or, maybe a touch of borax? Just enough to get the water a little bit soft? </p>

<p>Won't there be minerals in the next batch of well water that you run through it? Might be sisyphean.</p>

[wcroninger]

<p>John, <br>

Thanks for the thoughts, will try them out and see. I took a trial at using white vinegar last night with no luck. But your suggestions are definitely worth a go. Yes I do expect this to be a recurring problem LOL. But one thing I've found over the years is that the cleaner you keep the darkroom the more the students seem to be willing to assist in its maintenance!<br>

Bill</p>