What makes a dilution? (A "I feel stupid" kind of post)

I mean, I know what a dilution is, but for some reason I've been going around in circles trying to figure this one out. Is 1+1 always 1+1 as long as you have a minimum amount of developer and an equal amount of water?

To start with: I've been developing almost all my films in D-76 undiluted. This is what I was taught, and it was easy to follow since I had all the times in my head for different films and ratings. But now I want to try a 1+1 dilution (not for any cost savings, but for specific development advantages).

However, I'm a little confused with all the information out there concerning what is the correct amount of developer needed per roll of film. Many people say between 100-150 ml per roll (135, 120, 4-4x5 sheets), although Steve Anchell writes that 250 ml is ideal for proper development. Again, I'm not trying to save on using developer, I'm just trying to find the best way to go about it.

I have small tanks. I mainly use a 500 ml SS tank for one roll of 120 or one (or two) rolls of 135.

Until now, I have always just put one roll of film in the tank, and filled it up (I wasn't worried about wasting developer because I needed to use it up and I wanted to avoid any streaking or other development problems). That's stock. But can 250 ml still be considered stock if it's mixed with 250 ml of water? The amount of developer is considered stock but does the effect of water make it a 1+1 dilution? If I develop two rolls of 135 in a 500 ml tank filled with undiluted developer is that stock or can I consider that diluted?

Basically I guess my question is, if I want to develop my films in a 1+1 dilution in a 500ml tank, how much developer should I use, and how much water? I guess I'm trying to work out the differences between using 250+250 with one roll of film, or the same dilution with two rolls. Are they both considered 1+1 dilutions? Would the only difference be the times used to develop (I'm assuming 10% more for two films)? I want the tank to be filled to capacity.

I feel like quite a noob for asking, but I haven't been able to find any information that answers that question. A lot of the information that I've found assumes that people are using bigger tanks so that the dilutions make sense.

Stock is what the formula/package created to begin with. Once you start adding extra water it's no longer stock.

In general the question is does the diluted developer have enough developing power to handle all the film? IIRC Kodak only claims about 4 rolls for it's D-76. Ilford claims 8 for it's version [ID-11?] If you go with Kodak's numbers you'd need 250ml of stock for each roll. Plus any water needed to dilute. So you'd need a 1 litre tank to handle the 500ml of stock and 500ml of water. If you go with Ilford's you'd need 250ml of stock and 250ml of water. At least some of us find 8 rolls per 1 litre fine. Some I'm sure even claim more. Do some tests with non-critical film and see for yourself.

Think of 1+1, 1+4, 1+9 as ratios. Whatever the total volume, the goal of the ratio is to state 1 unit of stock + X units of diluent (water in this case). So, if you want to use 1+1, then it's equal amounts of stock and water to make whatever total volume you need.
To maintain the same amount of developer, your total volume will be higher (is the tank big enough?).

Here's the skinny from Kodak publication J-78 on D-76 developer:

If you use D-76 Developer diluted 1:1, dilute it just before
you use it, and discard it after processing the batch of film.
Before using the diluted developer, make certain that there
are no air bubbles in the solution. If air is coming out of the
solution and forming bubbles, let the solution stand until the
bubbles dissipate. Don’t reuse or replenish the diluted
solution. You can develop one 135-3 roll (80 square inches)
in 473 mL (16 ounces) or two rolls together in 946 mL
(one quart) of diluted developer. If you process one
135-36 roll in a 237 mL (8-ounce) tank or two 135-36 rolls
in a 473 mL (16-ounce) tank, increase the development time
by 10 percent

You can get the J-78 publication online on the Kodak website.

Dear Loose,
Don't feel stupid. As a math-impaired former history major, such things have long baffled me. One of my ways around such things is to use a replenished developer--in my case, D23. All I have to do is add the proper amount of replenisher to the stock bottle whilst the film is developing. At the end of the developing cycle, I just empty the tank back into the stock bottle. If there is any excess--there often is, I just dump the few ml down the drain. Of course, such a procedure does not help you if you are interested in comparing results of stock D75 vs 1:1 or doing other kinds of experiments. But using replenisher sure has simplified my darkroom life.

Once you start adding extra water it's no longer stock

So, if you want to use 1+1, then it's equal amounts of stock and water to make whatever total volume you need.
To maintain the same amount of developer, your total volume will be higher (is the tank big enough?).

Thanks Nick and Bethe, I think that's the confirmation I wanted -- basically 1+1 is the same as long as you've got enough developer. So if I wanted to do 2 rolls at the same time I would need a bigger tank in order to do it.

John -- I'm a former history major myself (before moving over to linguistics). That being said I started in chemisty but I guess it's been a while. I prefer to focus more on the photographic side of things than the technical details (but it sure helps when you know exactly what you're dealing with).

You can develop one 135-3 roll (80 square inches) in 473 mL (16 ounces) or two rolls together in 946 mL (one quart) of diluted developer. If you process one 135-36 roll in a 237 mL (8-ounce) tank or two 135-36 rolls in a 473 mL (16-ounce) tank, increase the development time by 10 percent


smieglitz -- I've seen this before too, but the confusion lies in the fact that at first they tell you to develop 2 rolls in a 946 ml tank but to process two rolls in a 473 ml tank for 10% longer. I guess they should clarify that to be in stock solution.

No. It's not stock solution. It reads as 1+1 to me. Stock solution (1+0) will be a shorter time regardless of the tank volume. You'll need at least 16 ounces or 473ml to physically cover two reels in a metal tank regardless wether it is diluted 1+0 or 1+1 or 1+2 ...

You need a certain amount of developer to process a specific area of film. What the above says is if you cut the total volume of 1+1 diluted developer you need to extend the time because their won't be enough stock in 473ml @1+1 to develop two rolls. You either have to extend the time with less developer volume, or increase the total volume of the working 1+1 solution.

winger said:

Think of 1+1, 1+4, 1+9 as ratios.

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But they are not "ratios". As noted here, they are what are called "parts", as in 1 part plus 1 part, 1 part plus 4 parts, and 1 part plus 9 parts, where the parts are equal volumes.

Ratios are notated with a colon. 1 + 1 equals a ratio of 1:2 (1 part plus 1 part = 2 parts), where 1 part is taken to a final volume of 2 parts. The ratio is read as "1 part to 2 parts".

For 1+4, this is written as 1:5 ("1 to 5", that is 1 part plus 4 parts = 5 parts), and 1+9 is the same as 1:10.

I oversimplified a bit, but it's easier to think of. And I meant the ratio of stock to water, not stock to total. My chemistry prof in college used to try and mess us up by switching between the two to see who caught it.
And have a BS in bio and a MS in forensic science and am so math-impaired it was a running joke with my past supervisor.

Winger, I believe you have it correctly.

Kirk, If I have it correctly, and I would be appreciative to know if I am wrong, you're right - BUT - you are right everywhere other than in common photographic usage, where the notation is used differently. I believe I have seen previous threads that touch upon this.

In the world of photography, the correct notation as you describe it is not generally used. It causes much confusion among others who wander into photography from other disciplines.

In photography a 1 to 1 blend means one part A plus one part B and is denoted 1+1 or 1:1
In photography a 1 to 2 blend means one part A plus two parts B and is denoted 1+2 or 1:2

One advantage to the common photographic notation is that it makes it easy to call out a more complex mix from a final formula that is comprised of several stock solutions - say from three stocks and water. For Example: ABC Pyro has rthree stock solutions, A, B, and C. It is easy to call out: "For tray development 1+1+1+7" or "For tank development 1+1+1+11"

Another benefit is that one needn't make any calculations to find out how much water is needed to add, since it is explicitly called out.

Regardless of what system is used, the plus sign is a much better way to denote the photographic usage, and lessens any chance of confusion. The : sign is used in photography as if it were the + sign.

C

The problem arises because some manufacturers used 1:10 or 1:20 quite correctly as Kirk says to mean dilute 100ml to 1 litre etc. In this instance 1:10 & 1:20 meant 1+9 and 1+19. Luckily that practice has stopped in photography

I have to admit that with Rodinal & now Pyrocat HD I always use the 1+50 & 1+1+100 to mean 10ml +10ml made up to 1 litre (for Pyrocat).

Some people use the colon incorrectly so it's definitely better to use the plus sign. FS is used in both instances to indicate a solution is used Full Strength.

Ian

CBG said:

In the world of photography, the correct notation as you describe it is not generally used. It causes much confusion among others who wander into photography from other disciplines.

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THis is true, and that's why we see so many of these types of questions over the years. I suggest adopting which ever notation you prefer, and using them correctly. Summing of parts is not the same as ratios.

CBG said:

In photography a 1 to 1 blend means one part A plus one part B and is denoted 1+1 or 1:1
In photography a 1 to 2 blend means one part A plus two parts B and is denoted 1+2 or 1:2

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Your examples are correctly written for summing of parts, but they are incorrect for the ratios. The 1+1 being equal to 1:1 is quite a common error.

CBG said:

One advantage to the common photographic notation is that it makes it easy to call out a more complex mix from a final formula that is comprised of several stock solutions - say from three stocks and water. For Example: ABC Pyro has rthree stock solutions, A, B, and C. It is easy to call out: "For tray development 1+1+1+7" or "For tank development 1+1+1+11"

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I agree that when using multicomponent developer stocks, it is sometimes easier to use parts summing.

But if you want to use a tank and you want 280 mls of solution in it, when using parts summing, you'll have to convert it to ratios anyway to figure out how to make it. 1+1+1+11 is equal to 1:1:1:14, and you take 280 ml and divide it by 14 which gives you 20 ml for each of the 3 components.

I'll leave it to you to show how you calculate volumes needed to make 280 ml when stating with 1+1+1+11 notation.

CBG said:

Another benefit is that one needn't make any calculations to find out how much water is needed to add, since it is explicitly called out.

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See the example above. Not always true when working with more complicated examples with odd volumes.

CBG said:

Regardless of what system is used, the plus sign is a much better way to denote the photographic usage, and lessens any chance of confusion. The : sign is used in photography as if it were the + sign.

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Your last sentence used to be right in it's observation, but I think more and more manufacturers are using ratio notation correctly. Ilford is very consistent, but some older Kodak stuff is ambiguous as to if ratio notation is what they really are using, as opposed to parts summing with ratios (colon punctuation sign : ) in the place of addition signs.

And, in larger dilutions, the difference can become small. 1+1000 and 1:1000 are not that difference. Only a difference in 1 part in 1000 parts.

If I saw a 1:1 dilution specified in a photography book, I would definitely assume that 1+1 was meant, and I think that most other people would do the same.

Chazzy said:

If I saw a 1:1 dilution specified in a photography book, I would definitely assume that 1+1 was meant, and I think that most other people would do the same.

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But what if you saw 1:10 ?