DK-20 ultra fine grain B&W developer (raw chemicals, experiences)

PeterFotolab · Oct 9, 2022

I don't know if there is already a composite theme for the DK20 developer. If not, I started one.

My question is:
about KSCN (Potassium Thiocyanate)

- It is possible to make a KSCN stock solution e.g. solution with a volume of 100 ml? ... I need to preserve KSCN.

A couple of years ago I bought KSCN 250gr, the warranty ended in 2018, now I started developing with DK-20 after a long break, and it seems to me that the result is not as fine-grained as when I started experimenting with fresh KSCN, already it is not that. I assume that it can be due to the non-functionality of KSCN to dissolve silver on the emulsion.

Does anyone know what she is shelf life of KSCN?

I was thinking of making a stock concentrate, e.g. into alcohol, or TEA, this is how a stock solution concentrate developer with VitC is made.

250 grams of KSCN lasts a long time, and throwing away the whole package every year is not a good idea.

Or do you know of another chemicals that will dissolve the silver halide with a similar property to KSCN?

ThankYou.

Anon Ymous · Oct 9, 2022

IIRC, potassium thiocyanate keeps indefinitely in solution. It's also very hygroscopic and will rapidly absorb humidity from the air. As a result, what you weigh on the scale has progressively less of the compound and more water. It would be a good idea to make a solution of known concentration, like 50% w/v, when you buy it.

Ian Grant · Oct 9, 2022

DK-20 was withdrawn in the US because of bad Dichroic fogging issues with US made Kodak films, it was made for a few years longer by Kodak Ltd in Europe as there was not a similar problem with British made Kodak films. It had to do with fall out from US atmospheric atomic tests affecting gelatin, and new techniques.

You can use Sodium Chloride instead of Thiocyanate, that was Kodak's approach with DK-20's replacement Microdo, then Microdol_X. Ilford released a data sheet P10 on this before releasing Perceptol.

Ian

PeterFotolab · Oct 9, 2022

Anon Ymous said:
IIRC, potassium thiocyanate keeps indefinitely in solution. It's also very hygroscopic and will rapidly absorb humidity from the air. As a result, what you weigh on the scale has progressively less of the compound and more water. It would be a good idea to make a solution of known concentration, like 50% w/v, when you buy it.

Thanks for the reply, but how to dilute it, how to dose it to achieve 1g of KSCN in solution form. Up to 1 liter DK-20 goes 1g Potassium Thiocyanate. What can I dissolve it in, just distilled water or some kind of preservative? Well thank you.

PeterFotolab · Oct 9, 2022

Ian Grant said:
DK-20 was withdrawn in the US because of bad Dichroic fogging issues with US made Kodak films, it was made for a few years longer by Kodak Ltd in Europe as there was not a similar problem with British made Kodak films. It had to do with fall out from US atmospheric atomic tests affecting gelatin, and new techniques.

You can use Sodium Chloride instead of Thiocyanate, that was Kodak's approach with DK-20's replacement Microdo, then Microdol_X. Ilford released a data sheet P10 on this before releasing Perceptol.

Ian

I have never experienced dichroic fog since using the DK20. I shoot primarily on Fomapan 400, no fogging occurred.

Does sodium chloride have the same properties for dissolving silver halide as Thiocyanate, to ensure a fine grain?

Anon Ymous · Oct 9, 2022

PeterFotolab said:
Thanks for the reply, but how to dilute it, how to dose it to achieve 1g of KSCN in solution form. Up to 1 liter DK-20 goes 1g Potassium Thiocyanate. What can I dissolve it in, just distilled water or some kind of preservative? Well thank you.

You take the 250g KSCN and dissolve it in deionised water, to a final volume of 500ml. You take 2ml of the solution for every gram of KSCN needed. The dissolution of KSCN in water is endothermic, the solution will get very cold.

Anon Ymous · Oct 9, 2022

PeterFotolab said:
I have never experienced dichroic fog since using the DK20. I shoot primarily on Fomapan 400, no fogging occurred.

Does sodium chloride have the same properties for dissolving silver halide as Thiocyanate, to ensure a fine grain?
Is it tried and tested?

Sodium chloride can be used to make a Perceptol - Microdol like formula. Search for Edgar Hyman's formula. It's actually very close to the commercial developer and gives very good results. Metol, sulfite and sodium chloride, that's all. There's a speed penalty of about a stop, but at the 1+3 dilution it still gives fine grain, is reasonably sharp and the speed penalty is reduced. I haven't noticed any dichroic fog with any films when using this formula. Modern films are probably much less susceptible to dichroic fog compared to old ones, which is probably why you didn't notice any when using DK-20.

PeterFotolab · Oct 9, 2022

Anon Ymous said:
You take the 250g KSCN and dissolve it in deionised water, to a final volume of 500ml. You take 2ml of the solution for every gram of KSCN needed. The dissolution of KSCN in water is endothermic, the solution will get very cold.

Sounds interesting. It just doesn't bother me that it will be a stable solution indefinitely. OK, the concentrate will be sealed in the bottle. Are there studies that KSCN will be stable in DI water, that it will not lose its effectiveness?

Anon Ymous · Oct 9, 2022

PeterFotolab said:
Sounds interesting. It just doesn't bother me that it will be a stable solution indefinitely. OK, the concentrate will be sealed in the bottle. Are there studies that KSCN will be stable in DI water, that it will not lose its effectiveness?

This has been my experience after keeping a solution for a couple of years or so. I don't have any sources about its longevity, that's something I remember reading, but haven't kept any references. If you are worried that it won't keep that well, weigh some freshly bought KSCN, like 50g and keep it sealed. Then you can make a solution whenever needed, without weighing it again, you already know how much you have, regardless of what it weighs then (it could have picked some moisture).

Ian Grant · Oct 9, 2022

PeterFotolab said:
I have never experienced dichroic fog since using the DK20. I shoot primarily on Fomapan 400, no fogging occurred.

Does sodium chloride have the same properties for dissolving silver halide as Thiocyanate, to ensure a fine grain?
Is it tried and tested?

Yes, Sodium Chloride works as well, probably in a slightly different way, but it's the results that count. I have tried it, and it worked well, but I don't want the drop in film speed.

I did test DK-20 many years ago and had no Dichroic fogging at all with FP4. It all comes from the same research papers, which I have somewhere.

Ian

DK-20 ultra fine grain B&W developer (raw chemicals, experiences)

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