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).

[table="width: 300"]

1:50
1+49


1:25
1+24


1:2
1+1


1:1
1

[/table]

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?

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

:munch:

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".

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

I prefer the notation 1+x because it can only be interpreted in one way.

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).

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

Vaughn said:

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).

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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

Like I said, great entertainment!

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.

Behind all this is some logic that gets missed. Say you're mixing a developer 1:100 (1+99) and need 1 litre, then you use a small accurate measure for the 10ml then pour this into a larger measure and then make it up to 1000ml (1 litre). This larger measure isn't likely to be accurate enough to measure 1010ml of 1+100.

Ian

MattKing said:

Like I said, great entertainment!

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Tons of fun!

A ratio of 1:1 meands life size in our case FS - Full strnght - as no dilution (or concentration) is taking place...

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Not following the logic of that one! LOL! In this case, 1:1 means that for every one unit of something (for example in a drawing) there is one unit of another thing (such as of the real item represented by the drawing). FS means full scale, not full strength...

But in spite of this silliness, Ralph nailed it -- good communication is the key! And I am afraid that Ian's last post fails the good communication test.

From Wikipedia:

"Dilution ratio
Ratios are often used for simple dilutions applied in chemistry and biology. A simple dilution is one in which a unit volume of a liquid material of interest is combined with an appropriate volume of a solvent liquid to achieve the desired concentration. The dilution factor is the total number of unit volumes in which your material will be dissolved. The diluted material must then be thoroughly mixed to achieve the true dilution. For example, a 1:5 dilution (verbalize as "1 to 5" dilution) entails combining 1 unit volume of solute (the material to be diluted) + 4 unit volumes (approximately) of the solvent to give 5 units of the total volume. (Some solutions and mixtures take up slightly less volume than their components.)
There is often confusion between dilution ratio (1:n meaning 1 part solute to n parts solvent) and dilution factor (1:n+1) where the second number (n+1) represents the total volume of solute + solvent. In scientific and serial dilutions, the given ratio (or factor) often means the ratio to the final volume, not to just the solvent. The factors then can easily be multiplied to give an overall dilution factor.
In other areas of science such as pharmacy, and in non-scientific usage, a dilution is normally given as a plain ratio of solvent to solute."
(end of citation)

In photographic processes, 1:50 means that in a total volume 50 units, 1 unit will be the developer (or other agent) and the rest (49 units) will be water (or other solvent).

A long time ago, Kodak decided to avoid any misunderstanding by adopting an additive notation, such as 1+49 (which is basically the same as the 1:n+1 notation mentioned a above). Kodak's notation is crystal clear: 1 unit of the principal agent is added to 49 units of solvent, whichs gives a total volume of 50 units.

1:50 (1 to 50 or 1 in 50) means that the agent is 1/50 of the total volume of 50, from which we can infer that the solvent is 49/50 of the total. As Kodak expresses, 1+49 to make up 50 units.

Similarly, if we want to use the agent undiluted, the scientific notion would be 50:50 (50 units of the total volume would be the agent and there would be no solvent. Thus, the reduced fraction 1:1 means undiluted (that is, 1 unit of agent plus 0 units of solvent) or 1+0, which is usually called "stock", which means straight out of the bottle or as initially prepared from dry ingredients according to the manufacturers basic formula.

Vaughn said:

FS means full scale, not full strength...

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In photography some manufacurers use the term F.S. with developers that can be use at Full Strenght or also diluted 1+1 and 1+3 etc, but yes FS is full scale in other photographic applications like copying, but we can have a ratio in this case so 1:1 is also applicable

I did qualify because we don't use a ratio like 1:1 with dilutions as it's meaningless, how can you have a one sided ratio when there's no dilution or concentration

What's important is accuracy and some manufacturers used to put both 1:10 (1+9) or similar on their bottles/datasheets to prevent inaccuracies.

Ian

Benoît99 said:

A long time ago, Kodak decided to avoid any misunderstanding by adopting an additive notation, such as 1+49 (which is basically the same as the 1:n+1 notation mentioned a above). Kodak's notation is crystal clear: 1 unit of the principal agent is added to 49 units of solvent, whichs gives a total volume of 50 units.

1:50 (1 to 50 or 1 in 50) means that the agent is 1/50 of the total volume of 50, from which we can infer that the solvent is 49/50 of the total. As Kodak expresses, 1+49 to make up 50 units.

Similarly, if we want to use the agent undiluted, the scientific notion would be 50:50 (50 units of the total volume would be the agent and there would be no solvent. Thus, the reduced fraction 1:1 means undiluted (that is, 1 unit of agent plus 0 units of solvent) or 1+0, which is usually called "stock", which means straight out of the bottle or as initially prepared from dry ingredients according to the manufacturers basic formula.

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Unfortunately Kodak in the US seemed to think differently Someone there got confused by the + and the :

So in British publications Kodak would say 1+1 & 1+3 and in the US 1:1 & 1:3 and mean the same thing, go figure that one out. The : symbol is used in maths (Mathematics) as a Ratio not as a + (plus) sign

Ian

If you change definitions depending on what field you are working in, you are ambiguous.

From Wikipedia:

In mathematics, a ratio is a relationship between two numbers of the same kind[1] (e.g., objects, persons, students, spoonfuls, units of whatever identical dimension), usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two[2] which explicitly indicates how many times the first number contains the second (not necessarily an integer).[3] In layman's terms a ratio represents, simply, for every amount of one thing, how much there is of another thing. For example, supposing one has 10 pairs of socks for every pair of shoes, the ratio of shoes:socks would be 1:10 and the ratio of socks:shoes would be 10:1.

I took a modification of this for my above post.

This shows you that some people do not know that things are often wrong on the internet. A ratio is a ratio regardless of usage. Math defines the term. The above, in my post here and previously, is the correct definition.

You do what you wish. You can even define things any way you wish. That does not make them right. I suspect an errant photographer or poster here probably edited the post on dilution ratios.

PE

I've never worked for Kodak, but the way I was taught in undergrad is the same as PE has it. 1:49 is the same as 1+49. Though most of the time we did things by % volume.

Concerning the notation for dilution; as a fellow student in chemistry was fond of saying, "That's not ambiguous that's amtriguous."

Bethe;

10% is 1:9 or 1 ml in 9 ml etc. So, yes I understand. I do most things by weight as the volume changes when you mix many things together. I also measure many viscous things which are difficult to measure by volume. Weight is easier. I must remind anyone who wishes to be critical of my using weight, consider that I usually measure in the dark when measuring out emulsions and 10% gelatin for addition to an emulsion. So, weight is handy.

But, thanks for the confirmation. I think often that no one these days is properly trained in math, or has ever taken a real lab course.

PE

But, thanks for the confirmation. I think often that no one these days is properly trained in math, or has ever taken a real lab course.

PE

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I suck at math, but I do have a BS in bio (we had to take chemistry for that, too), a MS in Forensic Science, and worked in a lab for 14 years.

"Ratio" in English has two meanings, which in Italian can be rendered as "rapporto" in one case, and "proporzione", which I think is translated exactly by the English word "proportion".

The first case, rapporto, or quoziente, is expressed with / or something to that effect.

If I say that 4/5 of APUG forum participants do not write in proper unambiguous English the second member, the divisor, is the "total"* of the two groups of APUG participants, and the first, the dividend, is those for each five participants who cannot use unambiguous English.

If I say that the proportion between those who can use unambiguous English and those who cannot is 1:4, I say the same thing expressed as a proportion.

Those two kinds of notation, 1:4 and 1/5 or 4:1 and 4/5 are, if I get it right, both termed "ratio" in English.

This is made worse by the fact that / and : are alternative signs for "division", and although it is customary to use / for "rapporto" and : for "proportion" this subtleties can go lost for writers of instruction booklets.

A trained person always reads 1:10 as "one to ten" (eleven parts in total) but many would read it as 1/10. It would be called a "ratio" in both cases correctly but the dilution would be different.

I guess in Italian and in other languages the ambiguity would be resolved because it would be specified "a proportion of 3:10" or "un quoziente di 3/13". In English you are pretty much stack with "ratio" which is "irrational" a way to express oneself (quotient, proportion should find larger use).

Fabrizio

* OK it's not the "total" you get what I mean...

Fabrizio;

The ":" is never used alone for division. It is formed from a dash through the colon (terrible double meaning here! ). The notation 1/10 is still one tenth which is 10% or 1 + 9 or 1:9. More a function of math than English I think.

PE

1: 9 1+ 9
its the same as saying
salt and paper
or salt n'peppa

"whatever it is" : or + ( added to ) " whatever it is"

the worst is when it is 1:9:1 and there are only 2 things being mixed !

Just as a side note, from way back when....

Back at the origin of chemistry and photography, things were expressed in parts such as:

7 parts Metol
3 parts HQ
0.5 parts KBr
25 parts Sodium Carbonate
and 1000 parts water

Regardless of the measurement units used, Grams, Ounces, Millifarkles or whatever, the ratios always came out right using YOUR units. And, they made up molal solutions not molar. So, that is the origin of many of our formulas and procedures. Everything was assumed to be in ratios or parts, not the native measures.

So, if parts were grams you have:

7 grams Metol
3 grams HQ
0.5 grams KBr
25 grams Sodium Carbonate
1000 grams of water

This way you can read very old formulas and come up with something workable.

PE

The title of this thread is an oxymoron.
The discussion of the topic is both futile and moot.

For example Kodak publication j86 on T-max developers does not use either notation! It state the dilution as follows:

You can easily mix smaller volumes by mixing one
part of the concentrate with four parts water.

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