# Chemistry: Ratios

Discussion in 'B&W: Film, Paper, Chemistry' started by Bruce Osgood, Nov 27, 2004.

1. ### Bruce OsgoodMembership CouncilCouncil

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Is a ratio of 1:2, 1 part X plus 1 part Y to make 2 parts or is it 1 part X plus 2 parts Y to make a combined 3 parts?

Would a PMK developer that calls for combing parts of 1:2:100 yield 100 ml or 103?

2. ### leeMember

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No, Bruce, your second answer is the correct. To reiterate, it is one part of Y and two parts of x

103 is the correct answer. I use 100 ml with 200 ml with 1000 ml for PMK. Sometimes with 4x5 I use 50 ml +100 ml + 500 ml because the tray I use for the developer is smaller.

Just maintain the 1+2+100 and you will be ok.

lee\c

3. ### jim appleyardMember

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I see that more folks are going to the the "+" sign when talking about mixing chemicals. It leaves no doubt that way.

4. ### Ian GrantSubscriber

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That's always been the way here in the UK

1+9 = 1:10
1+1 = 1:2

It's far less ambivalent

Ian

5. ### jim appleyardMember

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Ian, we're a little slow here in the US; look who got re-elected!

6. ### dancquMember

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So, 1:1 = 1+0 ?

I don't read it that way. I read 2:5, two parts to five parts,
two ml to five ml, etc. That's a ratio : . Dan

7. ### leeMember

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I agree with Dan (dancqu) 1:2:100 = 1+2+100

lee\c

8. ### Bruce OsgoodMembership CouncilCouncil

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Then, if you are saying "to", you mean 2 parts diluted "to" five parts, this will yield five parts total. In this case 1:1 would equal 1+0, or 'full strength'.

But if you mean "to" to mean + (why not say +) you would have 7 parts in total.

This is my question. Resolved: In photographic chemistry : seens to mean +. In the future I will use the plus sign and hope Anchell etal do the same.

thanks to all

9. ### JorgeInactive

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Sorry, but 1+9 is not equal to 1:10.
1+9 is 1 part of liquid added to 9 parts of other liquid. 1:10 is one part of liquid added to 10 parts of another liquid. In reality, photographic solutions should be expressed in percentages. IOW, a 10% solution by volume would be 1+9, but not 1:10.

So for example mixing Xtol at 1:2 is adding 1 part of Xtol concetrate to 2 parts of water and this in effect is a 33.33% solution.

10. ### leeMember

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In this case 1:1 would equal 1+0, or 'full strength'.

Bruce, I don't see it that way. I see it as one part x and one part y. Would that not yeild 50%?

the symbol : and the symbol + mean the same thing to me.

lee\c

11. ### David A. GoldfarbModeratorStaff MemberModerator

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As I understand it, among non-photographic chemists, there is a difference, but in photographic chemistry, the + and : are used interchangeably. I've taken to using the + symbol to avoid the ambiguity.

12. ### dancquMember

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The plus, "+", is what I used now and then. Using it is a step
towards spelling it out.

Now I don't think the + should be used. Using it is a step away
from the universally used : for denoteing ratios. Dan

13. ### dancquMember

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I nor yourself in your OP did mention "diluted". Ratios, one : one,
1:1, one to one, 1 to 1. The convention is the colon, : . Dan

15. ### djklmnopMember

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Oh come on guys, must you make photography this complicated???

16. ### Dean WilliamsMember

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Bruce;
When you are working with photographic chemistry, make it easy on yourself and change all the colons ":" to plus signs "+". This is the way it should be expressed anyway.

True ratios will just mix you up, and in reality can't normally be expressed in an easy way when using more than two like quantities (like mls). In other words, the PMK "ratio" is expressed incorrectly simply because it has more than two quantities. It should be 1+2+100, and that's really the only way it makes sense here.

Just in case you want to know, to express a developer dilution of (one part Dektol plus two parts water) in a ratio, it would be written 1:3. The second numeral of a ratio (the three in the Dektol example) is the total of parts needed for the solution. The first numeral (the 1) indicates one of the parts that make up the total, in this case the Dektol. Mechanical ratios work the same way, (think of two pulleys, one three times the size of the other). The larger pulley is three feet in diameter, the smaller one foot. One rotation of the larger rotates the smaller three times. A ratio of 1:3.

If this is all mush to you, just go back to my first sentence and mix with confidence.

17. ### dancquMember

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So then a dilution of 1:1 would be a solution with one part of the
first numeral and zero parts of what ever else; the second numeral
minus the first equalling zero. "The second numeral of a ratio...is
the total of parts... .

Any wonder I'm not convinced?

18. ### JorgeInactive

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Thank you! I was wondering if I was the only one who saw the problem.

19. ### Mark LayneSubscriber

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Talk about a tempest in a teapot. Get back to work fellas

20. ### Lee ShivelyMember

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I used to know how to mix photographic chemicals. Now I have no idea what I'm doing. Send help. My head is about to explode!

21. ### Dean WilliamsMember

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Look, I just put that last part in there in case Bruce wanted to know how a TRUE ratio was figured.

If we all just replace the colon in a dilution with a plus it will save a lot of head scratching. Remember that first of all.

When Kodak says "D76 1:1" they mean one part D76 and one part water. I don't know why they use the ratio thing here (the colon) instead of a plus sign. It's been used for a long time though, and they probably won't change it. I'm sure the chemists who work for Kodak know the difference between a ratio (expressed with a colon) and additive notation (expressed with a plus sign). We want additive notation to make things easier, and, so things like a ratio of 1:1 don't cause so much misunderstanding.

The definition of a ratio is: "The relation of two quantities of the same kind." So, the ratio of:

1:0 is a misnomer. You can't have a ratio with only one quantity

1:1 is what we call stock solution. One part developer in a total of one part. That's a 100% solution.

1:2 is half stock and half water.... and so on.

There are three ways to express a ratio, and maybe this will help clear things up: 1:1 or 1/1 (like a fraction) or 1 divided by 1. If you use the fraction method you will see that a 1:1 ratio is 1 or for our purposes, stock solution.

Again, Kodak uses the colon to denote an additive notation, while Ilford and Agfa (and others) use the more conventional plus sign.

Just remember to replace the colon with a plus sign and all this ratio stuff won't matter.

22. ### photomcMember

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Good explanation Dean..next point is just keep doing what you have been, if you start changing everything - well IT IS Like STARTING OVER.

23. ### Bruce OsgoodMembership CouncilCouncil

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Now that works for me. Thank you.
1 (Stock) + 1(Water) = a 50% Working Solution.
1 (Stock) + 2(Water) = 33.33% Working Solution.

24. ### JorgeInactive

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I have never heard of true ratios or false for that matter. But the important thing is that it does not matter. As long as you use the notation in the way you understand it consistently you are in good shape. The explanation that 1:10 means one part in a total of ten parts seems unecessarily complicated, If we are going to use scientific notation, we would be talking about solutions with a precise specific gravity, or solutions with molarity, molality etc, etc.

In the end if you make 1 part in 9 or 1 part in 10 the difference is so slight as to have no impact in processing, so people, just do it the way you understand it and do it that way always and you will be fine...

25. ### TPPhotogMember

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I am so happy that Rodinal states 1+25; 1+50 or 1+100 and my Ilford chemicals 1+4 or 1+9 much much easier to understand. After all as we soup our negs we are cooks not scientists LOL

But as already said as long as the dilutions are consistant for your own use, does it really matter. Remember if you always make the same dilution then it becomes a standard for your use and that's all that matters.

26. ### dancquMember

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I sympathize. I read a thread similar to this a year or two ago
at rec.photo.darkroom. I'd always used the universall convention
of the colon when expressing ratios. I've returned to darkroom work
after many years absence.

I read a number of posts declaring that the unique nature of
photographic chemistry sets it apart from all else when expressing
ratios. So, I adopted the + ; 1+1+8 rather than 1:1:8. The first
reads one part A PLUS one part B PLUS eight parts C while the
second reads one part A TO one part B TO eight parts C.

To make a long story short, I've gone back to the universally
used convention of the colon when expressing ratios. The colon
is just TOO universally used. I think I've been using it for at
least 50 years and not been once out of line in doing so. Dan