View Full Version : Dichroic spots ?

11-May-2017, 01:43
I recently came across a phenomena I have never seen before: I processed HP5+ in Xtol 1:1 and irregular shaped spots appeared on the dried negatives. Diameter ~2mm, sometimes none, sometimes 3 per frame (sorry it's 120, nevertheless I hope on feedback please).

When looking through the negative you can not see them, but if you print (say the spot is in the sky) they print darker, which is odd, you expect a higher density with a spot, not lowering density.

After printing I looked carefully at an angle, and saw these blue/green coloured small stains/spot (again looking through you cannot see them). Spots were both on the emulsion and non-emulsion side. (afterthought: might the colour be responsible for the lower density ? Perhaps I should try printing on fixed grade paper ?)

Their appearance made me think of dichroic fog. I did try pure fixer on one of them, but that did not remove it.

I might try Farmer bleach, but that I can only apply to the non emulsion side (if it works at all).

The only reason for this phenomena is the Xtol I used: I always have to filter it before use, all my bottles of Xtol show a precipitate (although I used distilled water to make it up), and I always filter the working solution through a coffee filter; thus-far it never gave a problem.

The rest of my chemistry/procedure is sound, judged by a recent roll in home made Xtol (Mytol), the rest fixer etc are the same as the HP5 roll.

Any help appreciated,



11-May-2017, 03:15
What did you process the film in???

And what fixer did you use???

Steve K

11-May-2017, 03:20
I think this is one of the instances where a picture says more than a thousand words. It sounds like an interesting phenomenon for sure sounds it may be difficult to track down.

Given the color of the spots, the first thing that comes to mind is antihalation dye not being washed out entirely. Rewashing the negatives should help in this case. But I'm not sure if hp5+ in 120 has an antihalation dye that matches the color of your spots.

11-May-2017, 03:52
Are you using tap water for mixing your solutions??? Sometimes loose iron can cause spots in some solutions... (It can get past filters, or I have seen flux used to braze S/S dev reels sometimes dislodge onto developing film... Clean your S/S reels in an ultrasonic cleaner sometime, and you might see a sludge leftover inside the cleaner...) I have seen them cause spots... Magnify them and see if you can see a "nucleus" with the spot around them...

I just pulled down the first photo book I could reach, (Focal Encyclopedia of Photography) and looked up "dichroic fog" and it mentioned a bath in the following solution;

Thiourea 1.4 grams

Citric acid 1.4 grams

Water to make 125 c.cm

(I quote) Dichroic fog may be caused by excess of sulfite in a fine grain developer, by hypo contamination of the developer, by traces of developer in the fixing bath, or by insufficient fixing...

But I'd check for iron in solutions... (Sometimes excess iron can be released if local water line construction is happening, or just plain old bad plumbing where you live... Really flush out water lines, and change filters in the lab...) That might explain just some spots here or there...

Steve K

11-May-2017, 05:05
Thanks for the feedback.

To answer in one:

I used my last bottle of commercial Xtol (guess I mixed that one 2 years ago). What I always do/did: I solute the dry chemicals in MilliQ water (lab grade distilled water) and dispense aliquots (250 ml for 120 film or 4*5 film) stock in glass bottles, and fill them up to the brim with distilled water. The last 2 batches of Xtol showed a fine precipitate. Also others on this list (Sal I believe) reported the same problem. Before use of such a bottle I would filter the stock solution over a coffee filter, and fill up to 500ml with distilled water for single shot 1:1.

So I guess that rules out iron contamination, I have never seen these spots before until this last bottle of Xtol

Koraks; I do not think that it's the anti halo layer: first I always pre-rinse before development, and pour off a blackish rinse and second the spots are also on the emulsion layer.

I try to make a photograph, won't be easy though.

I'll mix the thiourea/citric acid bath and see what happens,



11-May-2017, 08:47
Do you use a stop bath?

11-May-2017, 10:58
No but I never did in all my processing over 25 years, and never saw these spots


Do you use a stop bath?

11-May-2017, 13:36
It only takes one time. I've always used stop bath and have never had dichroic fog. Assuming that's what the problem is why not try it.

16-May-2017, 10:36
a follow up,

First 2 photo's (kinda hard to photograph the spots) of the spots on the negative and on print:



The citric acid/thiourea did not work, nor fixing them out with pure fixer. Only left with Farmers, but that can only applied on the non-emulsion side. My hunch that the green/blueish colour kinda works as a lower density filter (the spots print darker) seems to hold: I made lith prints ( on old AGFA Record Rapid fixed grade paper, the example above is on Ilford MG IV RC)
of this roll, and the spots were almost invisible, if you did not know were to look you would not notice.

For lack off a better explanation I assume these spots are deposits of the Xtol precipitate and not some silver build up..