What changes adding hypo clearing agent to selenium toner?

BHuij · Nov 7, 2025

I know back in the day that it was common advice to mix selenium toner with hypo clearing agent or other wash aids, though I can't remember why. Seems these days the more common advice is to just mix your toner with water and use it to exhaustion.

I've been doing the latter for several years, any print I'm going to keep goes through KRST mixed 1:9 with plain old tap water. Works great.

Today I did something dumb, and when mixing up my jug of wash aid (I just use sodium sulfite, haven't bought actual hypo clearing agent in a long time), I accidentally dumped it into my selenium toner jug instead of my jug of water. Oops. It still toned my prints as normal. Have I somehow compromised my 1:9 KRST by adding all that sulfite, or should I just continue business as usual until I hit the exhaustion threshold where I would normally toss it and mix up new?

mshchem · Nov 7, 2025

BHuij said:
I know back in the day that it was common advice to mix selenium toner with hypo clearing agent or other wash aids, though I can't remember why. Seems these days the more common advice is to just mix your toner with water and use it to exhaustion.

I've been doing the latter for several years, any print I'm going to keep goes through KRST mixed 1:9 with plain old tap water. Works great.

Today I did something dumb, and when mixing up my jug of wash aid (I just use sodium sulfite, haven't bought actual hypo clearing agent in a long time), I accidentally dumped it into my selenium toner jug instead of my jug of water. Oops. It still toned my prints as normal. Have I somehow compromised my 1:9 KRST by adding all that sulfite, or should I just continue business as usual until I hit the exhaustion threshold where I would normally toss it and mix up new?

I formerly used Kodak Hypo Clearing Agent when mixing Se toner. I think I picked up the habit from Kodak and Ansel books in the 80's. It may be best practice, I don't know.
My current procedure is I use "film strength" fixer, fresh with constant agitation for about 90-120 seconds, rinse the print for 15-30 seconds in a tray of fresh water, then straight into the Kodak Rapid Selenium toner 1+3 (1 toner, 3 water), all at 68-75°F. Toning is to my liking but it's fast. Warm tone papers like Fomatone require more dilute toner to have more control of the Toning, but 1+3 works fine. After toning quick rinse then into fresh hypo clear 2-3 minutes with agitation. Then a couple minutes of fresh water gentle wash, then into archival washer.

Personal taste is (currently) using water alone to mix up the toner.

koraks · Nov 7, 2025

BHuij said:
Seems these days the more common advice is to just mix your toner with water and use it to exhaustion.

@Doremus Scudder has posted about this many, many times and I recommend at least trying his approach, because it really does work: don't discard your selenium toner. Just replenish it from time to time.

I've never seen the need to mix it with anything other than tap water.

If your KRST works with the sulfite added, I wouldn't worry about it. It wouldn't surprise me if the regular formulation of the KRST concentrate already contains a good amount of sulfite. There's also some ammonium thiosulfate in it and if anything, the sulfite should help to avoid its decomposition.

DutchDarkroom · Nov 7, 2025

I checked my memory and the art of photography and have found this:
Many photographers used to add HCA to their selenium toner, why exactly i'm not sure my guess would be for convenience. They would then throw away the toner when the HCA stopped working, which it does much more rapidly than selenium toner, Back in the day chemistry was cheap and environmental concerns were not known of so this wasn't seen as a problem. Now everyone i know off has switched to a seperate HCA bath (after toning) so they can use their selenium for longer. As for your situation, your selenium is usable but most likely not for as long as normal. Now i do wonder if you could extend that life by still using a secondary HCA bath or if the HCA also affects the toner itself...

Something related, does anybody know if it is necessary to wash prints before toning after they have been in a secondary fixing bath or if you can go straight from fix 2 to selenium toner? (so the process would be dev, stop, fix, holding bath and at the end of the day holding bath, fix 2, selenium toner, HCA and final wash)

koraks · Nov 7, 2025

DutchDarkroom said:
Something related, does anybody know if it is necessary to wash prints before toning after they have been in a secondary fixing bath or if you can go straight from fix 2 to selenium toner?

Experiences vary and I think the ultimate conclusion is that it depends. In principle you should be able to go from fix straight to selenium toner, but I think there have been problems in particular with certain fixers (alkaline as I recall) when doing this. Personally I only tone after an initial wash of 10+ minutes, but this is also a practical choice since I can batch up my prints towards the end of the session and then tone everything in one go. Or even tone them on a next occasion after initial evaluation of the prints.

DutchDarkroom · Nov 7, 2025

For me it would be more practical, although i could take prints from the holding bath into the fix and back into the holding bath and wash them for a bit. I currently use ilford rapid fixer which i is acidic (ph 5.0-5.5), kodak rapid selenium toner contains 25-30% ammonium thiosulphate so i can't imagine a little fixer on a print would significantly change this. Based on ammonium thiosulphate already being in the toner and if your recollection is correct most problems occuring with alkaline toners i would come to the conclusion that is has to be perfectly fine. However i have no experience with this and i wouldn't like to risk it.

koraks · Nov 7, 2025

I think the problems people have experience when going from fix straight to toner can be tracked to (1) remaining silver salts in the fixer reacting with the toner to form stain and/or (2) developer carry-over into the toning bath. IDK for sure which is the main culprit, only that a few people have (also recently) reported such problems.

DutchDarkroom said:
if your recollection is correct

That's always the $1m question, haha! I do know for sure that we have seen reports of staining problems with selenium toner not too long ago on the forum, as well as people reporting that a fix-direct-to-toner workflow works just fine for them. I take from this that it's case-specific and that you need to be alert to any problems, and adjust your workflow on signs of staining.

DutchDarkroom · Nov 7, 2025

I searched a bit more on this and experiences are very very mixed. What is reported most is going from an acidic fixer straight into selenium tends to leave stains, but it is also reported that ilford rapid fixer (which to my knowledge is acidic) works fine and is also called an alkaline fixer by some people on here. Unfortunately there is no final judgement in darkroom methods so i guess we will never know certainly. My theory (based on what others have also said) is that it might have to do with water quality and so results will vary. I might test going straight from fixer into selenium to see if i get stains since there are reports stains come quickly, not on a long term basis. Or i will just take a couple extra minutes to wash my prints and be certain i'm doing it right.

koraks · Nov 7, 2025

DutchDarkroom said:
My theory (based on what others have also said) is that it might have to do with water quality and so results will vary.

That's exceedingly unlikely unless the water for some reason has extreme amounts of very uncommon contaminants in it. Within the normal range of tap water - no way it'll have enough buffering capacity to shift pH to whatever turns out to be problematic, and presence of calcium salts will also not be a problem (it may make photographic solutions cloudy, but won't stain paper or film). Excess iron in water can be a problem, but is uncommon in tap water because this is one of the compounds that's removed by default through aeration followed by flocculation.

Either way, processes with a a fairly rigorous rinse/wash between fixing and staining are unlikely to present a problem, while attempts to shorten the process are inherently more risky and may or may not work. I think that makes the choice a fairly easy one if you factor in the labor that goes into making a decent print.

DutchDarkroom · Nov 7, 2025

You seem to know a hell of a lot about water! I wonder what may cause these differing results then. Anyway i agree that it's not worth the risk for most people and i'll figure out a way to wash prints between fixing and toning. Thanks for the help!

mshchem · Nov 7, 2025

When fixed prints are immersed in KRST and a stain appears it's an indication that your fixer is exhausted. A minute or 30 seconds intermediate wash in gently running water between fixer and selenium is adequate. Staining indicates insoluble silver halides remain, have not been removed by the fixing bath.

BHuij · Nov 7, 2025

DutchDarkroom said:
Something related, does anybody know if it is necessary to wash prints before toning after they have been in a secondary fixing bath or if you can go straight from fix 2 to selenium toner? (so the process would be dev, stop, fix, holding bath and at the end of the day holding bath, fix 2, selenium toner, HCA and final wash)

I won't pretend my n=1 results generalize to anyone else, but using my normal materials and chemicals, this almost perfectly describes my printing process. I'm using Ilford MG FB paper, E-72 developer, Kodak indicator stop bath, TF-5 fixer, KRST, and plain sodium sulfite as wash aid in place of HCA.

Every print goes through developer, stop, and 2 minutes in a neutral 1st fixer bath, then into a water holding bath until I'm done exposing paper for that day. Sometimes that's 15 minutes in the water holding bath, sometimes it's 4 hours.

When everything for that session has been fixed the first time, then I pull out the prints I'm actually going to keep from the holding bath, and put them in a second TF-5 bath for 2 more minutes. A quick but thorough 20-second rinse is all I do between that second fixer bath and toning, usually toning for ~5 minutes (at this point the lights are on so I can just kinda tone by eye). After the toner, they go straight into a separate wash aid. I mix up the wash aid bath at the start of the print session and just use it the one time before discarding. Finally into the running water for a final wash.

So I haven't experimented with going straight from 2nd fix into toner, but even with just a brief rinse in between those steps, I haven't seen staining from the toner in years. In fact the last time I saw staining, it was the reason I finally decided to adopt a 2-bath fixing regimen.

It sounds like the general consensus is that in the past, photographers were combining selenium toner with HCA for the convenience of having "tone the print" and "kill the residual fixer" as a single step, and then discarding it when the HCA was dead, simply because the HCA was dead, even if the selenium in there was still perfectly capable of toning.

Hopefully my little oops with the sulfite doesn't actually compromise my toner in any way. I believe you're correct that KRST concentrate itself contains both some sodium thiosulfate and probably some sodium sulfite. I should be able to tell without much trouble over the next several times I use it if the toner isn't behaving as expected. But I'm already doing the wash aid as a separate step, so I'll plan on just continuing as if my toner was mixed only with water until a compelling reason to worry presents itself

Thanks all!

pentaxuser · Nov 7, 2025

mshchem said:
then straight into the Kodak Rapid Selenium toner 1+3 (1 toner, 3 water), all at 68-75°F. Toning is to my liking but it's fast. Warm tone papers like Fomatone require more dilute toner to have more control of the Toning, but 1+3 works fine. After toning quick rinse then into fresh hypo clear 2-3 minutes with agitation. Then a couple minutes of fresh water gentle wash, then into archival washer.

Personal taste is (currently) using water alone to mix up the toner.

I wonder if your experience with Kodak Rapid Selenium at 1+3 indicates a major difference from Ilford Selenium. In the Ilford video on its Selenium Toner the presenter uses it at 1+3 and at that dilution she gets an amazing pinkish tone which I assume doesn't happen with Kodak Selenium

She uses a WT Ilford paper and sort of hints in passing that "other papers may produce a different tone So maybe the kind of tone she gets is confined to Ilford WT paper ?

Here's the video
Thanks

pentaxuser

MattKing · Nov 7, 2025

I think the practice of adding HCA to the toner came about historically because toner was cheap and usage was high and it saved time - all the sorts of things that apply more to a prolific printer or commercial user, but not to most users here.
In addition, the practice arose before the health concerns surrounding selenium toner were well understood, so disposal was not as likely to be a concern.
As far as going straight from fixer to toner, that practice was more common when people were using plain - not rapid - fixer, and were therefore probably contributing less silver load to the fixer bath, resulting in less silver carry-over.
I certainly wouldn't consider doing that unless I was using two bath fixing, and being conservative about how many 8x10 prints per bath.

mshchem · Nov 7, 2025

BHuij said:
I won't pretend my n=1 results generalize to anyone else, but using my normal materials and chemicals, this almost perfectly describes my printing process. I'm using Ilford MG FB paper, E-72 developer, Kodak indicator stop bath, TF-5 fixer, KRST, and plain sodium sulfite as wash aid in place of HCA.

Every print goes through developer, stop, and 2 minutes in a neutral 1st fixer bath, then into a water holding bath until I'm done exposing paper for that day. Sometimes that's 15 minutes in the water holding bath, sometimes it's 4 hours.

When everything for that session has been fixed the first time, then I pull out the prints I'm actually going to keep from the holding bath, and put them in a second TF-5 bath for 2 more minutes. A quick but thorough 20-second rinse is all I do between that second fixer bath and toning, usually toning for ~5 minutes (at this point the lights are on so I can just kinda tone by eye). After the toner, they go straight into a separate wash aid. I mix up the wash aid bath at the start of the print session and just use it the one time before discarding. Finally into the running water for a final wash.

So I haven't experimented with going straight from 2nd fix into toner, but even with just a brief rinse in between those steps, I haven't seen staining from the toner in years. In fact the last time I saw staining, it was the reason I finally decided to adopt a 2-bath fixing regimen.

It sounds like the general consensus is that in the past, photographers were combining selenium toner with HCA for the convenience of having "tone the print" and "kill the residual fixer" as a single step, and then discarding it when the HCA was dead, simply because the HCA was dead, even if the selenium in there was still perfectly capable of toning.

Hopefully my little oops with the sulfite doesn't actually compromise my toner in any way. I believe you're correct that KRST concentrate itself contains both some sodium thiosulfate and probably some sodium sulfite. I should be able to tell without much trouble over the next several times I use it if the toner isn't behaving as expected. But I'm already doing the wash aid as a separate step, so I'll plan on just continuing as if my toner was mixed only with water until a compelling reason to worry presents itself

Thanks all!

You have a darn good process there!

BHuij · Nov 7, 2025

Been working well for me!

mshchem · Nov 7, 2025

pentaxuser said:
I wonder if your experience with Kodak Rapid Selenium at 1+3 indicates a major difference from Ilford Selenium. In the Ilford video on its Selenium Toner the presenter uses it at 1+3 and at that dilution she gets an amazing pinkish tone which I assume doesn't happen with Kodak Selenium

She uses a WT Ilford paper and sort of hints in passing that "other papers may produce a different tone So maybe the kind of tone she gets is confined to Ilford WT paper ?

Here's the video
Thanks

pentaxuser

This is very similar to using Kodak toner. Warmtone papers will vary in response. Fomatone can produce all sorts of results

Raghu Kuvempunagar · Nov 7, 2025

BHuij said:
photographers were combining selenium toner with HCA for the convenience of having "tone the print" and "kill the residual fixer" as a single step,

This can't be true if the Selenium toner itself contains Ammonium Thiosulphate, the key ingredient of fixer.

MattKing · Nov 7, 2025

Raghu Kuvempunagar said:
This can't be true if the Selenium toner itself contains Ammonium Thiosulphate, the key ingredient of fixer.

Is it ammonium thiosulfate in selenium toner or is it sodium thiosulfate, or have both been used?

Ian Grant · Nov 7, 2025

MattKing said:
Is it ammonium thiosulfate in selenium toner or is it sodium thiosulfate, or have both been used?

Ammonium Thiosulphate.

I think AA added HCA to KRST, but a major component of HCA is Sodium Sulphite which is already present tin KRST. Early Kodak KRST may have had a different balance of chemicals.

Ian

Raghu Kuvempunagar · Nov 7, 2025

MattKing said:
Is it ammonium thiosulfate in selenium toner or is it sodium thiosulfate, or have both been used?

According to a Kodak patent it is Ammonium Thiosulphate:

Kodak Polytoner and alternative sepia/sulfide toners

If it has lost the deep oranage colour, then it is mostly gone. Well, the bottle I prepared with persulfate is less orange than the sulfide/sulfur preparation to begin with. I don't think much was happening anymore with the sulfur/NaOH bottle, so I've added another gram of hydroxide in the...

www.photrio.com

MSDS of Harman Selenium Toner mentions only Ammonium Thiosulphate:

https://www.ilfordphoto.com/wp/wp-content/uploads/2017/03/HARMAN-Selenium-Toner-13-GHS-H17.pdf

Ammonium Thiosulphate is more desirable for making concentrated solutions due to its solubility.

Andrew O'Neill · Nov 7, 2025

I only ever mixed KRST with water...and replenished, as mentioned by Matt. I keep the HCA treatment separate.

Doremus Scudder · Nov 7, 2025

I always transfer prints directly from second fix to toner and always have.
Staining will occur if you do this if 1) the fixation of the print is not adequate and there are non-water-soluble silver halides left in the emulsion or 2) if the fixer is too acidic. FWIW, I use Ilford Rapid Fixer or Hypam 1+9 and have never had a problem. I've also used TF-4 and Kodak Rapid Fix (print dilution). Problems with staining may occur with the stronger "film dilution" of Ilford and Kodak rapid fixers; I've never tried it. Bottom line, fix well and use a near-neutral or alkaline fixer. Or wash thoroughly before toning. That works too, it's just more time consuming.

The wash-aid step should be after fixing and a five-minute water rinse. The five-minute rinse before the wash aid is important and helps speed up washing according to Ilford. Mixing selenium toner with wash aid is wasteful if you toss the toner when the wash-aid is exhausted. If you keep the toner longer, then you don't have a wash-aid step at all. Better to do it separately and after the five-minute rinse.

I've written a lot here and over on the LF fora about keeping and replenishing selenium toner. I have two batches, one stronger, one weaker, that have been going for 10 years now. Toning is done by visual inspections and prints are removed from the toner when the desired tonal shift has been reached. When times get too slow, more stock toner solution is added to speed it back up. Amounts are not specific. Toner used this way needs to be filtered before and after use. I use regular coffee filter cones. Sometimes a batch will grow bacterial slime. If that's the case, it's better to toss it and mix fresh. I've only had that happen a time or two.

Best,

Doremus

Ian Grant · Nov 7, 2025

I'm still using the same bottle of working solution KRST that I began using in the mid to late 1980, It KRST just gets filtered every year or so and topped up with more concentrated fresh KRST to replenish it.

I need some more KRST but at the current price I won't bother, I'll just mix my own, I have enough Sodium Selenite to last me out . . . . . . . . . .

Ian

David Lindquist · Nov 7, 2025

In The Print, copyright 1983, in a footnote in the section on toning, Ansel Adams comments "...I have recently been advised by scientists at Eastman Kodak that there may be no advantage to mixing Hypo Clearing Agent, instead of plain water, with the selenium toner. However, since this was previously considered the preferred method, I am continuing with the use of Hypo Clearing Agent; I have used this system for many years with apparent success."

David

What changes adding hypo clearing agent to selenium toner?

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Kodak Polytoner and alternative sepia/sulfide toners

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