Concentrated Dektol stock solution

Emilio_ · Jul 27, 2024

Hello everyone,

I've recently purchased a package of Dektol powder to prepare 3.8 liters of paper developer. According to the instructions, the stock solution should be diluted 1+2 with water before use.

To save storage space, I'm considering making the stock solution more concentrated, reducing it by half (i.e., making 1.9 liters of stock solution) and then diluting it 1+6 with water (right ratio?).

Does anyone know if this approach would work effectively? Would it impact the performance or shelf life of the developer?

Thanks for your insights!

Best,

Emilio

xkaes · Jul 27, 2024

Sounds OK, but you might need that much water for everything to dissolve.

Doremus Scudder · Jul 27, 2024

All the components will likely not go into solution at that higher concentration. Kodak's recommendation are likely based on this. You can try, but if there is undissolved powder or sediment, you'll have to dilute more. Keep in mind that a very concentrated solution at 75°F will likely throw a precipitate at 65°F; in other words, take your minimum storage temperature into consideration.

Best,

Doremus

MattKing · Jul 27, 2024

I agree with all the posts above.
IIRC, the mixing directions specify mixing to a slightly more concentrated, smaller amount, and then diluting the resulting mix to 1 US gallon (3.8 litres). You can probably use that slightly more concentrated amount as your stock solution, with a corresponding slightly greater dilution to convert the stock to standard working strength.
By the way, if you were able to get it to a 1/2 gallon of double concentration stock, the necessary dilution to get to standard working strength would be 1 + 5, not 1 + 6 (convert the 1/2 gallon of "super stock" to the target amount of 3 gallons of working strength).

Emilio_ · Jul 27, 2024

MattKing said:
the mixing directions specify mixing to a slightly more concentrated, smaller amount, and then diluting the resulting mix to 1 US gallon (3.8 litres). You can probably use that slightly more concentrated amount as your stock solution, with a corresponding slightly greater dilution to convert the stock to standard working strength.

Yes, the instructions say to mix the powder in 3 liters of water and then add 0.8 liters after everything has dissolved. Now, I'm not sure what the ratio of the stock solution to water would be with this concentration. I’m also unsure if this would be very useful, as it might not save much space.

MattKing · Jul 27, 2024

Emilio_ said:
Yes, the instructions say to mix the powder in 3 liters of water and then add 0.8 liters after everything has dissolved. Now, I'm not sure what the ratio of the stock solution to water would be with this concentration. I’m also unsure if this would be very useful, as it might not save much space.

Well, it does mean you can easily split it into 3 one litre bottles.
And you can achieve the standard working solution from that "super stock" by mixing it 1 + 2.78, although I would probably round that to 1 + 2.75.
The exact mixing ratio isn't particularly important, but being consistent is fairly important.

cmacd123 · Jul 27, 2024

Emilio_ said:
Yes, the instructions say to mix the powder in 3 liters of water and then add 0.8 liters after everything has dissolved.

actually, not add 0.8 liters, but add water suficent to bring the total volume to 3.8 liters. the presence of the dissolved powder MIGHT increase the volume of the solution,and by doing to final addition you compensate for that. Most published formulas do the same thing, start with .7 Liters, add stuff and bring up to 1 liter.

RalphLambrecht · Jul 27, 2024

Emilio_ said:
Hello everyone,

I've recently purchased a package of Dektol powder to prepare 3.8 liters of paper developer. According to the instructions, the stock solution should be diluted 1+2 with water before use.

To save storage space, I'm considering making the stock solution more concentrated, reducing it by half (i.e., making 1.9 liters of stock solution) and then diluting it 1+6 with water (right ratio?).

Does anyone know if this approach would work effectively? Would it impact the performance or shelf life of the developer?

Thanks for your insights!

Best,

Emilio

shoudn't that be1+4 then? I believe more concentrated solutions have a longer shelf life.

Rudeofus · Jul 28, 2024

RalphLambrecht said:
shoudn't that be1+4 then? I believe more concentrated solutions have a longer shelf life.

If you do the math correctly, it's neither 1+6 nor 1+4, it's 1+5.

RalphLambrecht · Jul 28, 2024

Rudeofus said:
If you do the math correctly, it's neither 1+6 nor 1+4, it's 1+5.

I This is putting a knot in my brain. If it's regularly 1+2, then if the concentration doubles, it ought to be 1+4 or not?... Oh no wait; I got it now... It would help if you watered down your new stock solution 1+1 first and then 1+2 as recommended by Kodak. In both cases, you end up with 12 liters of working solution. I don't get how 1+5 would work. That would make 6 liters of somewhat higher concentration.

Ian Grant · Jul 28, 2024

I did some testing early this year and at double strength, so 1.9 litres, everything will dissolve while warm, the precipitate out what looks to be Metol and Carbonate overnight.

If you want a concentrated print developer, you need to replace the Metol with Phenidone or Dimezone, and the Sodium Carbonate with Potassium Carbonate and a small amount of Hydroxide. That's how commercial developers like PQ Universal, Liquid Dektol, etc, are formulated.

Ian

MattKing · Jul 28, 2024

RalphLambrecht said:
I This is putting a knot in my brain. If it's regularly 1+2, then if the concentration doubles, it ought to be 1+4 or not?... Oh no wait; I got it now... It would help if you watered down your new stock solution 1+1 first and then 1+2 as recommended by Kodak. In both cases, you end up with 12 liters of working solution. I don't get how 1+5 would work. That would make 6 liters of somewhat higher concentration.

It is easier if you work in gallons - at least with this packaging!
It is designed to mix up into 1 gallon of stock solution, which in turn is diluted 1 + 2 to make 3 gallons of working solution.
So if you were able to make up a super stock solution of 1/2 gallon, you would need to dilute that 1 + 5 to again make 3 gallons of working solution.

Don_ih · Jul 28, 2024

RalphLambrecht said:
This is putting a knot in my brain.

Think of it this way: instead of 1 + 2 (Dektol plus Water), it's (1/2 + 1/2) + 2 ( (Dektol plus Water) plus Water) or 1/2 + 2.5. Much simpler

Don_ih · Jul 28, 2024

Incidentally, looking up the solubility of the various constituents of D72, the only thing that might precipitate out is Sodium Carbonate, if the the temperature drops enough. Everything else should easily dissolve in 1/2 the volume of water.

However - Dektol is a single powder in a package and it may not properly dissolve in 1/2 the recommended volume of water, because of whatever else is in it that makes it possible to be a single powder. When mixing a developer from scratch, it's important to add ingredients in a certain sequence and completely dissolve each before adding the next.

RalphLambrecht · Jul 28, 2024

MattKing said:
It is easier if you work in gallons - at least with this packaging!
It is designed to mix up into 1 gallon of stock solution, which in turn is diluted 1 + 2 to make 3 gallons of working solution.
So if you were able to make up a super stock solution of 1/2 gallon, you would need to dilute that 1 + 5 to again make 3 gallons of working solution.

Ha, got it.thanks

Emilio_ · Jul 28, 2024

Ian Grant said:
everything will dissolve while warm, the precipitate out what looks to be Metol and Carbonate overnight.

Not sure I understand what you mean...

ags2mikon · Jul 28, 2024

I tried it with D-72 and it didn't work. After about an hour on the magnetic stir it still had undissolved particles. I ended up just adding more water. D-72 is supposed to be the same as Dektol.

xkaes · Jul 28, 2024

How long does Dektol/D-72 stock last? I always mix from scratch, so I'm clueless.

Don_ih · Jul 28, 2024

ags2mikon said:
I tried it with D-72 and it didn't work. After about an hour on the magnetic stir it still had undissolved particles.

Undissolved particles of what, though? What stage didn't dissolve completely? You're not supposed to add the next ingredient until the previous one is dissolved.

john_s · Jul 28, 2024

Emilio_ said:
Not sure I understand what you mean...

Most chemicals are more soluble in warm water than in cold. So the extra powder chemicals in your double strength experiment will dissolve in warm water but can not stay in solution as it cools.

As someone said above, some substitution might enable success, for example, potassium salts are more soluble than sodium ones.

Rudeofus · Jul 28, 2024

xkaes said:
How long does Dektol/D-72 stock last? I always mix from scratch, so I'm clueless.

If you have stock solution, it lasts for many months. I develop my prints in stock solution, and the only reason I throw it out eventually is because I have lost so much due to carry over. Depending on number of prints it typically takes 6 months to reach this state. The solution does get darker over time, but it still works.

Doremus Scudder · Jul 29, 2024

Emilio_ said:
Not sure I understand what you mean...

Ian is saying that when the concentrated solution cools, the chemicals can no longer stay in solution and precipitate out.

Here's his (corrected) original reply: "everything will dissolve while warm, then precipitate out what looks to be Metol and Carbonate overnight [when the solution cools]."

Make sense now?

Doremus

xkaes · Jul 29, 2024

And some chemicals will precipitate out before others -- just like some liquids freeze before others.

Emilio_ · Jul 30, 2024

Doremus Scudder said:
Ian is saying that when the concentrated solution cools, the chemicals can no longer stay in solution and precipitate out

I see, thanks. Then 'to precipitate out' means that the melted grains solidify back in their original form...right? As I don't know this verb in English I could not grasp the sense of the sentence...

koraks · Jul 30, 2024

Emilio_ said:
Then 'to precipitate out' means that the melted grains solidify back in their original form...right?

Yes. They crystallize out usually at the bottom of the vessel. Sometimes they manage to create nice looking spikey crystals, sometimes it looks like white dust settling at the bottom.

You could try and figure out what the minimum volume of water will totally dissolve your developer. Then store it away and look at it after a few weeks. If anything has dropped out of solution, you can add some more water. Then when the weather cools in winter, you'll find you'll have to add some more water, still.

Alternatively, follow the manufacturer's instructions: you'll be done in 20 minutes and everything will work according to the documentation you have available to you in terms of storage life, dilution, development times etc.

If you want to vastly enhance shelf life while at the same time minimizing volume, consider making your own developers using dry/powdered ingredients. You can fairly easily buy things like hydroquinone, metol, phenidone, sodium or potassium carbonate, sodium sulfite, potassium bromide, benzotriazole etc. It's a bit more work obviously than buying a ready-made packet or bottle, but it gives the advantage of being able to mix only as much as you need, whenever you need it, the product will always be fresh, and it'll be cheap on a per-liter basis (not counting your hours of manual labor...)

Concentrated Dektol stock solution

Emilio_

xkaes

Doremus Scudder

MattKing

Moderator

Emilio_

MattKing

Moderator

cmacd123

RalphLambrecht

Rudeofus

RalphLambrecht

Ian Grant

MattKing

Moderator

Don_ih

Don_ih

RalphLambrecht

Emilio_

ags2mikon

xkaes

Don_ih

john_s

Rudeofus

Doremus Scudder

xkaes

Emilio_

koraks

Moderator

Concentrated Dektol stock solution

Moderator

Moderator

Moderator

Moderator

Privacy & Transparency

Privacy & Transparency