pH of Dektol or D-72, stock or working strength ??

bernard_L · May 11, 2021

Can someone please provide a measurement of pH of Dektol or D-72, stock or working strength (1+2). Many values are listed in:
https://125px.com/docs/techpubs/kodak/cis-61-2010_05.pdf
page 4 for B&W, but not for Dektol. And, yes, it is likely close to that for Duraflo RT, but I'd like a measurement, not guessing.
Someone is bound to ask "why do you need to know?". A: because I want to close loopholes in my process with D-72, now that "Kodak" Dektol is doubtful.
Thank you.

bernard_L · May 12, 2021

@michael_r Thank you.
Wish I would have a more definite number. Might have bought a bag of Dektol to make a measurement, but I read that the currently sold stuff looks strange, dark out of the bag.

Michel Hardy-Vallée · May 12, 2021

Have you tried mixing a batch of D-72 with distilled water and fresh chemicals? This should give you as best a pH reading as you can.

bernard_L · May 12, 2021

Michel Hardy-Vallée said:
Have you tried mixing a batch of D-72 with distilled water and fresh chemicals? This should give you as best a pH reading as you can.

Thank you for your response. Long version of the story. I did mix a batch of D-72. Had doubts. Measured pH of 0.1M Na2CO3: too low. Ditto with pool PH+: correct pH. So maybe my (old) Na2CO3 has hydrated and/or carbonated (transformed to NaHCO3) through many years of exposure to air. So I baked it for 1 hour at 170°C. No change. Possibly chemistry of sodium carbonate and related compounds is more complex in real life than in textbooks.

At this point it looks like I'll get better D-72 using makeshift carbonate from pool supplies than from a chemical supplies bag (admittedly old). In that awkward situation a check on the pH of the as-prepared stock solution would be helpful. Plus, the next step is debunking some "silver bullet" claims about paper developers. I had better make sure y chemistry is correct.

bernard_L · May 12, 2021

michael_r said:
The range of 10.2-10.4 for the working solution was always in the MSDS for Dektol.

Indeed; thank you for pointing this out. Note, however, that this URL:
https://www.freestylephoto.biz/pdf/msds/kodak/Kodak_Dektol_1464726_1464734.pdf
shows two versions of the MSDS in succession. he 2010 version lists the value of the pH. The 2012 version states "nor applicable". Deregulation?
Irrespective, I now have the information.

Rudeofus · May 12, 2021

I just mixed a batch of home brew D-72 for my dark room. I used ancient chemistry, with dark gray Metol and Hydroquinone. Sodium Sulfite and Sodium Carbonate were from moderately fresh containers (i.e. less than 5 years old).

The stock solution measured a pH of 10.4, with a falling tendency, i.e. I would start measuring a few minutes after mixing something like 10.45, and could watch it go down to 10.37 within a few minutes. I can't pin down an exact reason for this pH drop over time, but maybe falling temperature (I mixed the ingredients in hot water) plus dissolving aerial Carbon Dioxide plus ionic strength effects, I really don't know, and also did not wait for the pH to stabilize. When I diluted a small batch 1+2 with tap water, I would measure a stable pH of 10.6.

bernard_L · May 13, 2021

@Rudeofus Thank you. This confirms the information in the old MSDS. My cheap pH meter is probably accurate to no better than 0.05 even after calibration in buffer solutions, but the change might be observable.
The rise of pH when diluting is, to me, puzzling, but chemistry is a complex science.

Rudeofus · May 13, 2021

I also measured pH after the dark room session: 10.5. This tells me, that pH should end up somewhere between 10.3 and 10.7, anything else would indicate a mixing error or expired ingredients. Since both Metol and HQ are fully deprotonized at these high pH levels, slight differences in pH may not even matter all that much here.

Michel Hardy-Vallée · May 13, 2021

Not sure where you are based, but the chemicals from Photographer's Formulary are reliable for their intended purpose, and I use them regularly for my own mixes. They are an excellent baseline against which to compare other supplies.

Sodium carbonate is super-cheap and sold under many various guises, but before I use pool supplies or store-bought washing soda, I would at least compare a small sample of PF's stuff (which you can buy anhydrous or monohydrate) to whatever else you plan to use on a regular basis.

Most formulas are based on monohydrate, since it's more stable than anhydrous and won't absorb water from the air as quickly:
http://stores.photoformulary.com/sodium-carbonate-monohydrate/

Do yourself a favour, and start from good quality supplies, do all the reference measurements you need (pH, specific gravity, colour, developing time, whatever), and THEN you have something to compare your experiments with.

bernard_L said:
Thank you for your response. Long version of the story. I did mix a batch of D-72. Had doubts. Measured pH of 0.1M Na2CO3: too low. Ditto with pool PH+: correct pH. So maybe my (old) Na2CO3 has hydrated and/or carbonated (transformed to NaHCO3) through many years of exposure to air. So I baked it for 1 hour at 170°C. No change. Possibly chemistry of sodium carbonate and related compounds is more complex in real life than in textbooks.

At this point it looks like I'll get better D-72 using makeshift carbonate from pool supplies than from a chemical supplies bag (admittedly old). In that awkward situation a check on the pH of the as-prepared stock solution would be helpful. Plus, the next step is debunking some "silver bullet" claims about paper developers. I had better make sure y chemistry is correct.

bernard_L · May 13, 2021

Michel Hardy-Vallée said:
Do yourself a favour, and start from good quality supplies, do all the reference measurements you need (pH, specific gravity, colour, developing time, whatever), and THEN you have something to compare your experiments with.

Sensible advice. I live in France. My sources of photographic raw chemicals are either Disactis (France) or Suvatlar (Germany).

RPC · May 13, 2021

In this thread, Photo Engineer discusses how pH in developers containing hydroquinone change within a time after mixing, then stabilize:

https://www.photrio.com/forum/threads/what-are-we-talking-about-here-aging-of-d-76.25228/

Michel Hardy-Vallée · May 14, 2021

Indeed, that is one of the caveats of the original D-76 formula. Grant Haist suggested dropping hydroquinone altogether and adjusting the proportions of the other ingredients to achieve the same results.

RPC said:
In this thread, Photo Engineer discusses how pH in developers containing hydroquinone change within a time after mixing, then stabilize:

https://www.photrio.com/forum/threads/what-are-we-talking-about-here-aging-of-d-76.25228/

Michel Hardy-Vallée · May 14, 2021

Salutations du Québec. Ici on peut tout acheter de Photo Formulary, sauf les quelques produits classifiés comme l'hydroquinone. Heureusement on a Argentix pour ça.

bernard_L said:
Sensible advice. I live in France. My sources of photographic raw chemicals are either Disactis (France) or Suvatlar (Germany).

bernard_L · May 14, 2021

RPC said:
In this thread, Photo Engineer discusses how pH in developers containing hydroquinone change within a time after mixing, then stabilize:

https://www.photrio.com/forum/threads/what-are-we-talking-about-here-aging-of-d-76.25228/

Yes, I read that now and then on the interweb. In 2018 I mixed a gallon of D-76 and measured the pH as-mixed (once cooled to 25°C) and at intervals increasing from 12 to 24 hours over 3 days. No change within 0.02 units. Has anyone else actually performed that measurement?

Anon Ymous · May 14, 2021

bernard_L said:
Yes, I read that now and then on the interweb. In 2018 I mixed a gallon of D-76 and measured the pH as-mixed (once cooled to 25°C) and at intervals increasing from 12 to 24 hours over 3 days. No change within 0.02 units. Has anyone else actually performed that measurement?

Since you mixed a gallon of it, I assume it was store bought, not scratch mixed, right? If so, this is a better buffered version of D76, not the original formula. Perhaps closer to D76d.

bernard_L · May 14, 2021

Indeed, but I always found that statement unqualified, i.e. applying to any form of D-76, whether store-bought, original (2g borax) or D-76d (8g borax + 8g boric acid). Consistent with that quotation by the late PE, who should know (my emphasis):
https://www.photrio.com/forum/threa...g-about-here-aging-of-d-76.25228/#post-353613

A simple way to avoid this problem, which also takes place with Dektol btw, is to let it stand 3 days or about that, before using it.
The reason is simply, that hydroquinone reacts with oxygen and sulfite to form hydroquinone sulfonate which is less active, but it also forms sodium hydroxide which raises the pH. These two effects see saw back and forth as the activity of the developer gradually decreases with age.
It happens with any hydroquinone containing developer that is supplied in powder form. It is really no big problem after about 3 days. Then the developer, in my tests, stays constant for weeks until age finally begins to take over and it decays into developer death.

That is distinct from the long-term death of D-76 with H rising to 9.5 and activity... zero.

Anon Ymous · May 14, 2021

michael_r said:
Who said packaged D-76 is more buffered? I don't think that is correct.

If you search for an older D76 MSDS, you'll notice some listing both sodium tetraborate (borax) and boric anhydride. The formula used for the commercial product has changed in all these decades that it has been available.

john_s · May 14, 2021

And there's the D76 label from Australia:

D76 Kodak Australia, packaging indicates 4.5% Hydroquinone, 4.6% Borax and 1.8% Boric Acid

copied from http://www.lostlabours.co.uk/photography/formulae/developers/devD76_variants.htm

There is a photo of the label on the web somewhere. (Australian MSDS docs often had more detail, presumably because of local regulations.)

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