# Dilution question

Discussion in 'B&W: Film, Paper, Chemistry' started by shuttershane, Feb 17, 2012.

1. ### shuttershaneMember

Messages:
30
Joined:
Feb 14, 2012
Shooter:
Medium Format
So I am a little confused. So I am going to try developing my first roll of b&w film with Rodinal. The dilution recommended is 1:25

I have a Patterson Universal which I understand holds 500ml. How do I calculate 1:25 for 500ml?

Is it like this?
500/25 = 20
500 -20 = 480

So that would mean 20ml of Rodinal go into 480ml of water?

Or am I totally missing something here?

2. ### clayneMember

Messages:
2,805
Joined:
Sep 4, 2008
Location:
San Francisc
Shooter:
Multi Format
There's a million threads on this, but in short...

devel = 500 * 1/25 = 20
water = 500 - (500 * 1/25) = 480

And at these dilution levels, the disparity between 25 or 26 total parts is not going to make or break things.

I recommend you use 1:50 for your first time, though.

3. ### shuttershaneMember

Messages:
30
Joined:
Feb 14, 2012
Shooter:
Medium Format
OK cool, thanks Clayne. I will take your suggestion and do a 1:50.

Sorry I know its been covered but I kept seeing conflicting answers...but your explanation about the disparity eases my mind.

I developed film a very long time ago but that's when I was in school so all is forgotten

4. ### clayneMember

Messages:
2,805
Joined:
Sep 4, 2008
Location:
San Francisc
Shooter:
Multi Format
Whenever you see 1:50, within photo-circles and depending on who you're talking to, it could mean anything from 1 part dev, 49 parts water or 1 part dev, 50 parts water. That's why you'll commonly see 1+49, because it's clear it's 1 part dev, 49 parts water. In reality though we're talking .2ml variation - not enough to matter.

5. ### R.GouldMember

Messages:
943
Joined:
Apr 22, 2010
Location:
Jersey Chann
Shooter:
Medium Format
Simple anwser, divide the total required I:E 500 by the dilution +1, in your case 25, so divide 500 by 26,round it up very slightly, and you have your dilution, 20 to 480, this works for any dilution, and came from Patterson many years ago. one suggestion, when using Patterson tanks it is better to put a bit more developer in the tank, I would suggest 600, which at 1/25 works out at 24 developer to 576 water,as patterson reels can slip very slightly up the center colum, and leave a fraction of the film out of the chemicals,
Richard

6. ### chuck94022Subscriber

Messages:
732
Joined:
Jan 11, 2005
Location:
Los Altos, C
Shooter:
Multi Format
Agree with Richard, and will add that if you have a multi-reel tank, use both reels (set the empty one to take up the slack on the column), put the reel with film at the bottom of course. This will reduce the chance of the reel coming up out of the fluid.

Messages:
8,814
Joined:
Sep 19, 2003
Location:
K,Germany
Shooter:
Multi Format
excactly!

8. ### Tony-SMember

Messages:
807
Joined:
Aug 16, 2009
Location:
Fort Collins
Shooter:
Multi Format
Yes, that's correct. And it is a 1:25 dilution or, what I prefer, 1+24.

9. ### Tony-SMember

Messages:
807
Joined:
Aug 16, 2009
Location:
Fort Collins
Shooter:
Multi Format
That's perfectly fine for large dilutions, but when one talks about D-76 at 1:1 (undiluted) vs. 1+1 (1 part D-76 and 1 part water; i.e., 1:2 dilution) it is two very different things in chemistry parlance.

10. ### Steve SmithMember

Messages:
9,135
Joined:
May 3, 2006
Location:
Ryde, Isle o
Shooter:
Medium Format
So is a 1:1 dilution 1+0?

I think it's only chemists who think of 1:25 as one part in a total of twenty five. The rest of us think of it as ratio i.e. one part to twenty five parts.

So 1:1 would be the same as 1+1 i.e. equal quantities of developer and water.

Steve.

11. ### shuttershaneMember

Messages:
30
Joined:
Feb 14, 2012
Shooter:
Medium Format
Thanks for this reply. I plan to attempt all of this later today. You guys rock with all the great suggestions.

Last night I watched tv while practicing putting 120 film onto the reels. I think I have this part down.

12. ### Tony-SMember

Messages:
807
Joined:
Aug 16, 2009
Location:
Fort Collins
Shooter:
Multi Format
Yes, undiluted. Mathematically, it's the easiest way and least prone to confusion and error.

You should think of it for what it is - a dilution factor; "one divided by twenty-five". That way you can easily determine volumes so long as you know the final volume you need. For instance, if you need 750 ml at 1:25 it would be:

725 ml / 25 df = 30 ml of developer
725 ml - 30 ml = 695 ml of water
--------------------------------------
30 ml of developer plus 695 ml of water is a total of 725 ml at 1:25

Yes, I was corrupted by my high school photography teacher, too, nearly 40 years ago! Fortunately, I was straightened out by a college biology professor (who also taught photography in the department).

But 1:1 is a ratio, i.e., 1/1, which equals 1. And anything divided by 1 is undiluted, in this case, straight D-76.

Last edited by a moderator: Feb 18, 2012
13. ### Thomas BertilssonSubscriber

Messages:
15,665
Joined:
Jan 21, 2003
Location:
Minnesota
Shooter:
Multi Format
This could be overcome by stating, simply:
One part of Rodinal, to 24 parts water.
D76 undiluted.
One part D76 to one part water.

That, to me, surpasses the 'least confusing' criteria, because it isn't even confusing at all.

14. ### fotchMember

Messages:
4,809
Joined:
Mar 16, 2005
Location:
SE WI- USA
Shooter:
Multi Format
I have to agree with Steve on this. I am not corrupted by a chemist background however, I do have common sense. I may also add, it has always worked right, never a problem.

15. ### Steve SmithMember

Messages:
9,135
Joined:
May 3, 2006
Location:
Ryde, Isle o
Shooter:
Medium Format
I know we have discussed this before but I have always thought of it like this:

1:3 can be stated as 1 to 3. i.e. one part of something to three parts of something else.

Steve.

16. ### Tony-SMember

Messages:
807
Joined:
Aug 16, 2009
Location:
Fort Collins
Shooter:
Multi Format
But unfortunately Kodak uses 1:1 while Ilford uses 1+1, thus the potential problem. If they say in their data sheet "one part D76 to one part water" then that would be fine. But they don't.

I'll assume that you don't mean I don't have common sense.

And that's fine for you, but when communicating information to others, especially those who are new, 1:1 is more readily screwed up than is 1+1.

But to me, and many others, "1 to 3" is one part developer and 2 parts water. The "+" symbol is unequivocal while the ":" symbol isn't.

17. ### Bruce OsgoodMembership CouncilCouncil

Messages:
2,626
Joined:
Sep 9, 2002
Location:
Brooklyn, N.Y.
Shooter:
Multi Format
Simply put, it is a RATIO not arithmetic.

A 1:3 ratio means one part something to make 3.

1 + 3 is not a ratio, it is arithmetic and means 4.

" i.e. one part of something to three parts of something else." would equal 4 and is arithmetic.

18. ### Thomas BertilssonSubscriber

Messages:
15,665
Joined:
Jan 21, 2003
Location:
Minnesota
Shooter:
Multi Format
I know that; my little recommendation was more of a dream scenario than anything. My own philosophy is to try to never use abbreviated expressions, because they cause confusion usually, as evidenced here.

19. ### clayneMember

Messages:
2,805
Joined:
Sep 4, 2008
Location:
San Francisc
Shooter:
Multi Format
Guys, can we please not have another 500 page thread on a topic we've all beaten to death already?

I think we all know that depending on which field one is working with, 1:1 could mean straight/undiluted, because of parts vs total parts, but it's very well known to all of us, that within photo-circles, it is not parts vs total parts, but instead parts vs other parts. And since we're almost always dealing with something:water, common sense should translate 1:1 as half this, half that.

The only people who take issue with this are the ones who cannot adapt to the "corruption" of the measuring systems being used. However, I will once again reiterate that nobody ever said that it's ratio of one part : total parts, even with the ':' notation. 1:1 makes perfect sense if you think about it as parts : other parts.

If you see D-76 1:1 and you mix it straight because 'chemistry books say so damn it!' then you're not using common sense.

20. ### RalphLambrechtMember

Messages:
8,814
Joined:
Sep 19, 2003
Location:
K,Germany
Shooter:
Multi Format
the trouble wiyh common sense is thst it isn' very common.

21. ### Tony-SMember

Messages:
807
Joined:
Aug 16, 2009
Location:
Fort Collins
Shooter:
Multi Format
If only it were qualitative or quantitative. But unfortunately, it's subjective.