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  1. #1

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    Consensus on the notation of dilutions

    I've noticed that a lot of people, here and elsewhere on the 'net, use the colon and plus sign interchangeably to indicate dilutions. For example,

    Rodinal 1:50 / Rodinal 1+50

    Isn't there a difference? (albeit a very small one).

    1:50 1+49
    1:25 1+24
    1:2 1+1
    1:1 1

    I don't think it matters whether you dilute 1+50 instead of 1+49, but the last two lines of the table above could be really confusing. Technically, 1:1 is a stock dilution (undiluted), but if you use + and : without noting the difference, you end up with a 1+1 (that's 1:2 using the colon) dilution. Quite a difference.

    Maybe I'm just wrong about all this, so please correct me if I am. I just wanted to know if there's a consensus among you fine people. How does one indicate dilutions in a standardized and non-confusing way?
    And the sign said, "long haired freaky people need not apply"

  2. #2
    Photo Engineer's Avatar
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    Strictly speaking 1:50 and 1+50 mean the same to me and to most chemists and technical people. Same goes for 1:49 and 1+49..

    1:50 gives 51 parts and 1:49 gives 50 parts. It is normal to mix up to a given total such as 50 parts or 10 parts.

    So, a 10% solution is 1:9 or 10 ml of A and 90 ml of B.

    PE

  3. #3
    MattKing's Avatar
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    This question always brings rise to great entertainment.

    Basically, there is little consensus on the issue, because photographers come from different backgrounds (vocations and geographies) and the "norm" differs with those backgrounds.

    Personally, I prefer to either write out the instructions ("start with 100 ml of stock and add water to make a total volume of 250 ml") or use the shorthand of "1 + 24".
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  4. #4
    Ian Grant's Avatar
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    Walter, you're 100% correct in that 1+49 is the same as 1:50 etc. This 1:x is the scientific way of denoting dilution and used by the vast majority of people.

    One company breaks that rule though Eastman Kodak, why no one knows.

    Ian

  5. #5

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    I prefer the notation 1+x because it can only be interpreted in one way.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #6
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    I have always thought of it as ratios, with 1:31 yielding 32 parts with HC-110.

    1:1 as a stock solution without dilution just makes zero sense to me. Better (IMO) to use 1+0, or 1:0, but best to just say "stock solution".

    Disclaimer -- I am not a chemist. I am more use to thinking in terms of mathematics, and of roof pitches and steepness of trails where 2:9 is 2 units of rise to every 9 units of run).
    Last edited by Vaughn; 05-18-2012 at 02:54 PM. Click to view previous post history.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  7. #7
    Photo Engineer's Avatar
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    Well, let me try it this way then.

    1:49 says a ratio of 1 part concentrate:49 parts water. This makes 50 parts

    Or 1+49 says 1 part concentrate plus 49 parts water. This also makes 50 parts.

    So, I come out with both meaning the same to me and that is the way I was taught it as an undergraduate, a graduate and also as an engineer at Kodak.

    By no means can I make 1+49 equal to 1:50. If you say 1 in 50 this becomes ambiguous. You see, you never talk about ratio of one to the total, it is ration of one to another.

    A ratio represents, simply, for every amount of one thing, how much there is of another thing (NOT THE TOTAL). For example, supposing one has 10 parts of water for every part of developer, the ratio of developer:water would be 1:10 and the ratio of water:developer would be 10:1. The total number of parts would be 11. This would also be a 1+10 solution.

    PE

  8. #8
    Ian Grant's Avatar
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    Quote Originally Posted by Vaughn View Post
    I have always thought of it as ratios, with 1:31 yielding 32 parts with HC-110.

    1:1 as a stock solution without dilution just makes zero sense to me. Better (IMO) to use 1+0, or 1:0, but best to just say "stock solution".

    Disclaimer -- I am not a chemist. I am more use to thinking in terms of mathematics, and of roof pitches and steepness of trails where 2:9 is 2 units of rise to every 9 units of run).
    Your logic's right Vaugh

    A ratio of 1:1 meands life size in our case FS - Full strnght - as no dilution (or concentration) is taking place, 1:50 is a 1 part in 50 there's no ambiguity with that. 1+49 means the same as 1:50 but 1:49 means one part in a total of 49.

    What is a ratio like 1:1 or 1:50 it's well written about and not contentious either, see Dilution ratios.

    Ian
    Last edited by Ian Grant; 05-18-2012 at 04:32 PM. Click to view previous post history. Reason: add link

  9. #9
    MattKing's Avatar
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    Like I said, great entertainment!
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  10. #10
    RalphLambrecht's Avatar
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    i don't know about any consessus, but i enthusiastically vote for the 1+' typenotation, as i find it to be the lest con fusing and more helpful when mixing chemicals, of course it cold just be me and the strange ways my damaged brain works!others may have other preferences.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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