Mixed my own D-76 Low ph?

So I have been experimenting mixing my own chemicals with the help of the Darkroom Cookbook. I have been having an issue where the developers I mix seem to be less active than they should be. A fair amount less active. This has happened with D-23, divided and single bath, as well as D-76. Even developing for longer than I think I should be based off the Massive Dev Chart, I am ending up with very thin negatives. I know they are being exposed correctly.

TO help diagnose my issue I bought a PH meter. After calibrating it, my D-76 is reading a PH of 7.9. From what I am reading, it should be more in the range of 8.5. I am fairly sure I am not messing up the formula, and I have switched scales, so I think one of my chemicals is suspect, or monohydrated when I am expecting anhydrous etc.

Based on the fact I was having a similar issue with D-23 (I have not remixed and measured, but I can if necessary), it has to be either the sodium sulfite or borax. Is there an easy way to test this? I was thinking of taking the ph of a 10% solution of each or something, but I am having trouble finding what this ph should be. I slept through a few too many high school chem classes to understand it all. Can anyone help me with this information? Or if you think it may be something else, I am interested in your thoughts.

Thank you for any help

Are you using tap water? Check the pH of the water itself as one possibility.

"Developing" by CI Jacobson 1948 p67 gives the pH of a 10% solution of sodium sulfite as 9.7.
It may be worth checking to see that your sodium sulfite has not partially oxidized to sodium sulfate which solution has a pH ~7.

relistan said:

Are you using tap water? Check the pH of the water itself as one possibility.

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That won't make much of a difference unless the tap water is below 6 or so. Which it isn't.

vjuliano said:

I think one of my chemicals is suspect, or monohydrated when I am expecting anhydrous etc.

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Sodium carbonate usually does not come as anhydrous, but either as mono or sometimes deca. Verify what you have.
Of course this doesn't explain your problems with the sulfite. However, sulfite and borax are usually what you'd expect them to be.

It might be worth reading this question about mixing your own D76:

https://www.photrio.com/forum/threads/d-76-ph-elevation-with-storage.55838/

I have been making a few batches of it myself, both with metol and phenidone and they have both worked and continue to work as expected some months after mixing.

Terry S

Using the PH meter some more, Ive lost all confidence in its accuracy. It seems to drift off calibration almost instantly, and I struggle to get reproducible results. It does seem to be consistent in its indication that my D-76 PH is low though. So I am going to invest in a meter that isnt the cheapest amazon has to offer, I will continue my investigation when it arrives and post back here. Thanks for the help so far.

Thanks!

I just got a cheapie pH meter just to add a data point to my lab notes, and maybe to support mixing my own.

But isn't pH one of those measures you can kick up or down like adjusting a swimming pool? Mix up the D-76 to formula, check the pH and add a pinch of this or that to bring alkalinity up or down to where it needs to be?

After all, we change its pH pretty much when we mix it 1:1 don't we?

vjuliano said:

Using the PH meter some more, Ive lost all confidence in its accuracy. It seems to drift off calibration almost instantly, and I struggle to get reproducible results. It does seem to be consistent in its indication that my D-76 PH is low though. So I am going to invest in a meter that isnt the cheapest amazon has to offer, I will continue my investigation when it arrives and post back here. Thanks for the help so far.

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If it constantly drifts, then the batteries may be flat. Check with fresh batteries if you can.

koraks said:

That won't make much of a difference unless the tap water is below 6 or so. Which it isn't.

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You sound pretty sure of yourself. Have you tested OP’s tap water? I’ve seen it as low as 5 when testing. That will matter.

I’m no chemist but it sounds like a jug of distilled water would be more worthwhile than a Ph meter, unless you already tried distilled. Also chemicals of known purity and grade. As someone already mentioned the formulae should be self correcting if mixed properly.

michael_r said:

pH measurements are more of a requirement where the formula itself indicates something like after all the ingredients are mixed "add [sodium hydroxide] or [acetic acid] to pH X.X.

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I thought the developing agents depend on alkalinity for rapidity. So when adding water, part of the reason it takes longer to develop is that it's less alkaline.

An update, feeling that bad / less active chemistry was my issue, I decided to try to isolate the offender. Having had issues with DD-23 and D-76, I had a feeling Borax might be the issue. I mixed up a new batch of D-76 and DK-76, which is D-76 but with the Borax replaced with sodium metaborate. I used distilled water this time to remove this variable as well. Let both sit for a bunch of hours to settle then ran a test strip through each, using same time (7.5 min for Arista Edu Ultra 400). The D-76 was still very thin, but the DK-76 looked great. I then ran a full roll through and am very happy with the results.

This is surprising because the Borax is from the Photographers Formulary. Has anyone experienced anything like this before? Is borax prone to oxidation or aging?

Thanks for the help

then why the difference? and D-23 works as expected, just no speed gain from DD-23

I have been trying to get PH measurements, but I dont trust my ph meter. I figured identical solutions with a single variable was an alright experiment.