Concentrated Dektol stock solution

[Emilio_]

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]

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

 

[Doremus Scudder]

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]

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_]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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_]

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

Not sure I understand what you mean...

 

[ags2mikon]

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]

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

 

[Don_ih]

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]

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]

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]

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]

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

 

[Emilio_]

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]

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...)