Selenium toner dilution : help with a math problem

Alex Benjamin · Mar 21, 2025

I want to tone some Ilford warmtone fiber paper in Kodak selenium toner. Not sure what dilution to use between 1:9 and 1:20. Would like to try both.

Here's the math question I can't figure out:

If I start with 1 litre of the 1:9 dilution and don't like it, how much water should I add to reach 1:20?

If, on the other hand, I decide to start with 1 litre of the 1:20 dilution and don't like it, how much selenium should I add to get to 1:9?

MattKing · Mar 21, 2025

1 litre of 1:9 includes 100 ml of toner and 900 ml of water.
To turn that mix into 1:19 (for simplicity) working strength, that 100 ml of toner needs to be matched up with 1,900 ml of water. So to get the amount of water from 900 ml to 1,900 ml, add 1,000 ml (1 litre) of water.
You will end up with a total volume of 2 litres at the 1:19 strength.
We can work out the difference to make it 1:20, but are you sure you want to?
If you insist on 1:20, you need to end up with 20, rather than 19 parts water, so along with that 100ml of toner, you will have 2,000 ml of water, making for a total volume of 2,100 ml.

The second part of your question is more finicky.
1 litre of 1:20 dilution includes 1 part toner and 20 parts water. so the amount of toner in 1 litre is 1/21 x 1000 ml = 47.62 ml and the amount of water in that litre is the rest: 952.38 ml.
For 952.38 ml to be 9 parts, one part needs to be 105.82. So you have to add enough toner to bring the toner amount to that amount: 58.2 ml.

Alex Benjamin · Mar 21, 2025

MattKing said:
1 litre of 1:9 includes 100 ml of toner and 900 ml of water.
To turn that mix into 1:19 (for simplicity) working strength, that 100 ml of toner needs to be matched up with 1,900 ml of water. So to get the amount of water from 900 ml to 1,900 ml, add 1,000 ml (1 litre) of water.
You will end up with a total volume of 2 litres at the 1:19 strength.
We can work out the difference to make it 1:20, but are you sure you want to?
If you insist on 1:20, you need to end up with 20, rather than 19 parts water, so along with that 100ml of toner, you will have 2,000 ml of water, making for a total volume of 2,100 ml.

The second part of your question is more finicky.
1 litre of 1:20 dilution includes 1 part toner and 20 parts water. so the amount of toner in 1 litre is 1/21 x 1000 ml = 47.62 ml and the amount of water in that litre is the rest: 952.38 ml.
For 952.38 ml to be 9 parts, one part needs to be 105.82. So you have to add enough toner to bring the toner amount to that amount: 58.2 ml.

Thanks !!

Should have figured Matt would be the king of Math

GregY · Mar 21, 2025

Alex, my thanks to Matt for the math. I find the toning results depend on both the paper and the developer.
I find Ilford Warmtone to change colour very quickly.... My standard is 1:19..... i like to have time to pull the print out of the toner before it goes past the result i want. 1:9 will turn print colour of Ilford Warmtone super quickly....far too quickly for my taste.

pentaxuser · Mar 21, 2025

Looks like good maths, Matt or is that math in Canada as well

However, Alex, I doubt very much if rounding up to whole numbers for ease of using whole numbers of ml is likely to made any perceivable difference

pentaxuser

JerseyDoug · Mar 21, 2025

Alex Benjamin said:
I want to tone some Ilford warmtone fiber paper in Kodak selenium toner. Not sure what dilution to use between 1:9 and 1:20. Would like to try both.

Here's the math question I can't figure out:

If I start with 1 litre of the 1:9 dilution and don't like it, how much water should I add to reach 1:20?

If, on the other hand, I decide to start with 1 litre of the 1:20 dilution and don't like it, how much selenium should I add to get to 1:9?

Those two dilutions look a little odd in juxtaposition. 1:9 is more likely actually 1+9. But 1:20 is likely actually 1:20.

The math isn’t all that hard, but that level of precision is unnecessary. As long as you record what you did for each instance, simply adding another liter of water in the first instance and adding another 50ml of selenium in the second instance will be fine.

Here is the math, assuming that you really mean 1:9 and not 1+9: The liter of 1:9 dilution is 1/9 liter (111 ml) of selenium and 8/9 liter (889 ml) of water. To get to a 1:20 dilution starting with the same 1/9 liter of selenium you will need 19/9 liter (2.111 liter) of water in total. And since you already have 8/9 liter of water you will need to add an additional 11/9 (1222 ml) of water.

Plug 50ml of selenium and 950ml of water into the same math to get the answer for the second question

Alex Benjamin · Mar 21, 2025

JerseyDoug said:
Those two dilutions look a little odd in juxtaposition. 1:9 is more likely actually 1+9. But 1:20 is likely actually 1:20.

I used Kodak's notation. On the bottle, it does note 1:3, 1:9, 1:20, when describing the amounts of prints that can be toned per dilution.

GregY said:
I find Ilford Warmtone to change colour very quickly.... My standard is 1:19..... i like to have time to pull the print out of the toner before it goes past the result i want. 1:9 will turn print colour of Ilford Warmtone super quickly....far too quickly for my taste.

I'll probably start with 1:20, or rather 1:19, as Matt suggests, and go to 1:9 if I don't find it strong enough. My feeling is that these will be my two extremes. I'll find something in the middle if neither satisfiy me.

JerseyDoug said:
The math isn’t all that hard, but that level of precision is unnecessary. As long as you record what you did for each instance, simply adding another liter of water in the first instance and adding another 50ml of selenium in the second instance will be fine.

Works for me.

mshchem · Mar 22, 2025

I've used 1+3 KRST forever for cold and neutral tone papers. Depending on the paper it needs to be much more dilute for warmtone papers. Fomatone needs very dilute solution, for pretty much any toner. Been a while since I've used Ilford warmtone, but I would mix 500mL of 1+9, if it is too much too fast I would dilute to 1 L or a quart or so (US not Imperial quart speaking)

MattKing · Mar 22, 2025

I actually have a Bachelor of Science degree with a major in Physics - so the "math" bit comes fairly naturally.
As for the 1:20 vs 1+20 vs 1:19 vs 1+19: the confusion arises because of two different outlooks on the issue.
To whit, is the number on the right of the colon - the "19" in "1:19" - refencing the number of parts of dilutant or the total number of parts overall?
For whatever reason, the Kodak nomenclature has always referenced it to the number of parts of dilutant, and that is where I learned this stuff from.
I am given to understand that that isn't a universal understanding of the issue.

koraks · Mar 22, 2025

Alex Benjamin said:
If I start with 1 litre of the 1:9 dilution and don't like it, how much water should I add to reach 1:20?

If, on the other hand, I decide to start with 1 litre of the 1:20 dilution and don't like it, how much selenium should I add to get to 1:9?

From a practical viewpoint, it doesn't really matter. If the action is too limited/slow, add some concentrate. If it's too fast, add some water. Beyond this, it's splitting hairs unless you're using the toner one shot and you're toning an edition of identical prints that you want to make as identical as possible. And really, selenium toner shouldn't be used one shot to begin with; it's unnecessarily wasteful and releases more toxic selenide to wastewater than necessary.

Think about it - if you reuse your toner (which you should), it'll always be of basically undetermined strength after you've toned the first print. How much selenium will actually have been used? It depends on the depth of toning, as well as the silver density of the print. In practice, you don't really know how much selenide there's still left in your working strength toner after you've run a couple of prints through it. I don't know about you, but I simply look at how toning progresses and once it gets noticeably (annoyingly) slow, I just add some concentrate to restore its vigor.

So I really think it's not really an issue - a much more pertinent question is how you (visually) track the progress of toning. I'm sure you've figured that out, using some kind of visual reference (an untoned print/strip) or maybe just by the seat of your pants (which makes the dilution problem virtually irrelevant to begin with).

What I'm trying to say is - don't worry about it. This is one of those things where trying to be exact doesn't really result in a more accurate end result. Again, with the exception of the initial use case I mentioned above.

RalphLambrecht · Mar 22, 2025

I asked Claude and he said:
Let me solve this step by step:

For the first question: Starting with 1 liter of 1:9 dilution, how much water to add to reach 1:20?

In a 1:9 dilution, we have 1 part selenium to 9 parts water, which means:

Selenium: 1/10 of the total volume
Water: 9/10 of the total volume

In a 1:20 dilution, we have:

Selenium: 1/21 of the total volume
Water: 20/21 of the total volume

In 1 liter (1000 ml) of 1:9 dilution, we have:

Selenium: 1000 × (1/10) = 100 ml
Water: 1000 × (9/10) = 900 ml

The amount of selenium stays constant. We need to find the total volume (V) where:

100 ml of selenium = V × (1/21)
V = 100 × 21 = 2100 ml

So our final volume needs to be 2100 ml, meaning we need to add: 2100 ml - 1000 ml = 1100 ml of water

For the second question: Starting with 1 liter of 1:20 dilution, how much selenium to add to reach 1:9?

In 1 liter (1000 ml) of 1:20 dilution, we have:

Selenium: 1000 × (1/21) ≈ 47.62 ml
Water: 1000 × (20/21) ≈ 952.38 ml

The amount of water stays constant at 952.38 ml. In a 1:9 dilution:

Water (952.38 ml) = 9/10 of the total volume
Total volume = 952.38 ÷ (9/10) ≈ 1058.2 ml

So the new amount of selenium needed is: 1058.2 ml - 952.38 ml ≈ 105.82 ml

Therefore, we need to add approximately: 105.82 ml - 47.62 ml ≈ 58.2 ml of selenium

To summarize:

Add 1100 ml of water to convert 1 liter of 1:9 dilution to 1:20
Add 58.2 ml of selenium to convert 1 liter of 1:20 dilution to 1:9

Don_ih · Mar 22, 2025

While generally 1:9 means 1 per 9 (an end volume of 9), whenever it is written in photography I assume it means 1+9 (an end volume of 10).

@pentaxuser -- we call it "math". I remember reading "maths" when I was a kid and thinking that s would make the word irritating to say. I tried it a few times. Didn't like it. I decided it was an irritating habit from the old country to be discarded, much like insisting on using "an" instead of "a" before words that begin with a non-silent "h" (like "an historic event" -- which, when read aloud, sounds like "unhistoric event"). I can't recall if Bertrand Russell liked that "an" or not - he was irritating in other ways....

Ben 4 · Mar 22, 2025

If you have access to Tim Rudman's Photographer's Master Printing Course, you'll find a handy dilution table in the back as well. It doesn't explain directly how to go from one dilution to another, but it gives you a leg up by telling you exactly how much water and how much of your chemical you should have at each dilution level.

pentaxuser · Mar 22, 2025

Don_ih said:
While generally 1:9 means 1 per 9 (an end volume of 9), whenever it is written in photography I assume it means 1+9 (an end volume of 10).

@pentaxuser -- we call it "math". I remember reading "maths" when I was a kid and thinking that s would make the word irritating to say. I tried it a few times. Didn't like it. I decided it was an irritating habit from the old country to be discarded, much like insisting on using "an" instead of "a" before words that begin with a non-silent "h" (like "an historic event" -- which, when read aloud, sounds like "unhistoric event"). I can't recall if Bertrand Russell liked that "an" or not - he was irritating in other ways....

Thanks Don So you say and write "I have a degree in math or a math degree"? Math sounds strange to me perhaps because we in the U.K. always say maths so it might be just "conditioning" but equally it seems to make sense because mathematics has always seemed to be a study of numbers plural or symbols plural where the collective and singular noun math does not seem to describe it as well

Maths rather than math seems logical and is not in the category of say the phrase like "non inflammable" which I admit has always been confusing or the name spelt as Majoribanks but pronounced Marshbanks Finally Cholmondeley pronouced Chumley takes us to the territory of a comic sketch that might have been made for a conversation between Jed Clampett and his English butler

pentaxuser

Don_ih · Mar 22, 2025

pentaxuser said:
mathematics has always seemed to be a study of numbers plural or symbols plural where the collective and singular noun math does not seem to describe it as well

"A study" is singular.

Alex Benjamin · Mar 22, 2025

Ben 4 said:
If you have access to Tim Rudman's Photographer's Master Printing Course, you'll find a handy dilution table in the back as well. It doesn't explain directly how to go from one dilution to another, but it gives you a leg up by telling you exactly how much water and how much of your chemical you should have at each dilution level.

I do have it and stupid me didn't even think of looking there ! Thanks.

Alex Benjamin · Mar 22, 2025

Don_ih said:
we call it "math". I remember reading "maths" when I was a kid and thinking that s would make the word irritating to say. I tried it a few times. Didn't like it. I decided it was an irritating habit from the old country to be discarded, much like insisting on using "an" instead of "a" before words that begin with a non-silent "h" (like "an historic event" -- which, when read aloud, sounds like "unhistoric event").

pentaxuser said:
Thanks Don So you say and write "I have a degree in math or a math degree"? Math sounds strange to me perhaps because we in the U.K. always say maths so it might be just "conditioning" but equally it seems to make sense because mathematics has always seemed to be a study of numbers plural or symbols plural where the collective and singular noun math does not seem to describe it as well

Maths rather than math seems logical and is not in the category of say the phrase like "non inflammable" which I admit has always been confusing or the name spelt as Majoribanks but pronounced Marshbanks Finally Cholmondeley pronouced Chumley takes us to the territory of a comic sketch that might have been made for a conversation between Jed Clampett and his English butler

pentaxuser

In French it's always plural — les maths — but the "s" is not pronounced.

Ben 4 · Mar 22, 2025

I don't think one would (think of looking there, or in any of the books on our shelves)…I really don't know why that tidbit stuck in my mind. I think I acquired Dr. Rudman's book at a time when I was re-learning darkroom work and was hungry for information and guidance, poring over every page.

Don_ih · Mar 22, 2025

Alex Benjamin said:
In French it's always plural — les maths — but the "s" is not pronounced.

That really didn't help. Alex.

JerseyDoug · Mar 22, 2025

MattKing said:
I actually have a Bachelor of Science degree with a major in Physics - so the "math" bit comes fairly naturally.
As for the 1:20 vs 1+20 vs 1:19 vs 1+19: the confusion arises because of two different outlooks on the issue.
To whit, is the number on the right of the colon - the "19" in "1:19" - refencing the number of parts of dilutant or the total number of parts overall?
For whatever reason, the Kodak nomenclature has always referenced it to the number of parts of dilutant, and that is where I learned this stuff from.
I am given to understand that that isn't a universal understanding of the issue.

I had this same conversation with my father many years ago. We were looking at the data sheets for a variety of darkroom chemicals, some American and some German. His take on it was that 1+9 meant add 1 part of the concentrate to 9 parts of water, and 1:10 meant pour 1 part of the concentrate into the graduate and then add enough water to bring the level up to the "10" mark.

GregY · Mar 22, 2025

Don_ih said:
That really didn't help. Alex.

Neither does the sidetrack on etymology Don
BTW... as far as dilutions... Ilford instructions for fixer dilutions for example are 1 +4 or 1 +9.
I store my selenium toner in a 2 liter jug. ......so i use 100ml + 1900ml....
others' dilutions may vary.

pentaxuser · Mar 22, 2025

Don_ih said:
That really didn't help. Alex.

Yes it did. I was about to reply to that reply that this shows that we and the French do agree on things. My nation(the Scots) formed an an alliance with France many centuries ago

We better stop this now and call it a draw. It's way off the subject and I feel may only be amusing you and I. We are no doubt as one in our sympathies with those unfortunates saddled with the names of Majoribanks and Cholmondeley

pentaxuser

snusmumriken · Mar 22, 2025

Alex Benjamin said:
In French it's always plural — les maths — but the "s" is not pronounced.

Vaughn · Mar 22, 2025

koraks said:
...

What I'm trying to say is - don't worry about it. This is one of those things where trying to be exact doesn't really result in a more accurate end result. Again, with the exception of the initial use case I mentioned above.

Agreed. Just be consistent and judge by the results one gets.
And if one needs to transmit one's process to someone else, just make sure all are on the same page.

Don_ih · Mar 22, 2025

GregY said:
Neither does the sidetrack on etymology

No, but it's at least a bit more interesting.

JerseyDoug said:
His take on it was that 1+9 meant add 1 part of the concentrate to 9 parts of water, and 1:10 meant pour 1 part of the concentrate into the graduate and then add enough water to bring the level up to the "10" mark.

so they mean the same thing.

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