FX-2K

[consumptive]

Hi. I'm interested in trying out FX-2, however I don't have any of the potassium carbonate crystals on hand. However, I saw the formula listed online at Jack's Chemistry site:

http://www.jackspcs.com/fx2.htm

where a "K" variant is mentioned at the bottom:

"Replace the potassium carbonate with 225 g Kodalk (sodium metaborate). This variation, FX 2K, provides more flexibility with enhanced midtones."

Its my understanding that Kodalk and sodium metaborate are NOT the same thing. Has anyone tried this variant? My first edition Film Development Cookbook doesn't mention it. Is this legit? And is it Kodalk or sodium metaborate?

Thanks

 

[Tom Hoskinson]

Kodalk is Sodium Metaborate.

See: (there was a url link here which no longer exists)

You could also substitute Sodium Carbonate for the Potassium Carbonate. A more concentrated solution can be made with Potassium Carbonate than with Sodium Carbonate. You can also substitute other alkalis as long as you keep the working solution pH the same.

 

[nworth]

The specification here is for "Potassium carbonate crystals," which is very vague. It also states that this particular form is needed because of an unknown amount of bicarbonate contaminant, and it does not give a pH target for the developer. In other words, there is no hope of duplicating the original FX-2 - ever! The metaborate variation (FX-2K) looks like a good and safe substitute that will give you consistent results. In general, you can substitute sodium carbonate monohydrate for anhydrous potassium carbonate weight for weight (not an exact mole for mole substitution, but close enough), so long as the solution is not too concentrated to dissolve all the carbonate needed.

 

[Tom Hoskinson]

The specification here is for "Potassium carbonate crystals," which is very vague. It also states that this particular form is needed because of an unknown amount of bicarbonate contaminant, and it does not give a pH target for the developer. In other words, there is no hope of duplicating the original FX-2 - ever! The metaborate variation (FX-2K) looks like a good and safe substitute that will give you consistent results. In general, you can substitute sodium carbonate monohydrate for anhydrous potassium carbonate weight for weight (not an exact mole for mole substitution, but close enough), so long as the solution is not too concentrated to dissolve all the carbonate needed.

Yes:

Crawley's FX-2 Acutance Developer


Metol 0.25 gram
Sodium Sulfite (anhyd) 3.5 grams
Potassium Carbonate (Crystal) 7.5 grams
Glycin 0.75 gram
Pinacryptol Yellow 1:2000 solution 3.5 ml
Water to make 1.0 liter

From the BJP Annual 1970, page 213

Note: Crawley says nothing about Bicarbonate in the K2 CO3 + 1.5H2O (nor does J.T. Baker - for that matter)



Potassium Carbonate (Crystal) MW=165.24
Potassium Carbonate (Anhyd) MW=138.21

Sodium Carbonate (Anhyd) MW=105.99

Molecular weights from J.T. Baker

 

[gainer]

IOW, 138.21 g of Potassium Carbonate (Anhyd) exactly equal 165.24 g of Potassium Carbonate (Crystal) and if there's any doubt about what you have, heat the heck out of it before you weight it and treat it as anhydrous.

 

[Alan Johnson]

Geoffrey Crawley was uncertain of the exact formula carbonate he put in FX-2.From his article BJP Jan 6 1961:
"Potassium carbonate (cryst) B.P. K2CO3. 1 1/2 H20 gives an individual type of alkalinity not matchable with any direct equivalent form of potassium carbonate (dried).......the B.P. crystals must therefore be used in these formulae when specified.The type of alkalinity provided is useful as it is in practice less energetic than the other carbonates (due to the formation perhaps of some restraining bicarbonate?) and therefore allows a fairly large concentration to be present,which stabilses the activity of the solution.It seems to work very well with glycin, and was mentioned in this context 60 or 70 years ago"
A copy of British Pharmacopeia c1960 and a copy of a pharmacopeia describing the present potassium carbonate cryst. would be needed to find out if the original could be authentically matched.

 

[nworth]

The quote given by Johnson is somewhat more useful and specific than that given in the jackspec website, but it is still a bit vague. We are not sure what this "individual type of alkalinity" is or how it affects the image or why. The specification is still poor, and it is uncertain if the results could be matched. Certainly other forms of carbonate in equivalent amounts will work in this formula, but you can't guarantee just the same results Crawley got.

 

[Murray Kelly]

The FX-2K indeed looks like a good substitute, but 225g of Kodalk seems an awful lot to replace 75g of Pot. carbonate crystals. Does Kodalk have all that many more H2O molecules in it?

Murray

The specification here is for "Potassium carbonate crystals," which is very vague. It also states that this particular form is needed because of an unknown amount of bicarbonate contaminant, and it does not give a pH target for the developer. In other words, there is no hope of duplicating the original FX-2 - ever! The metaborate variation (FX-2K) looks like a good and safe substitute that will give you consistent results. In general, you can substitute sodium carbonate monohydrate for anhydrous potassium carbonate weight for weight (not an exact mole for mole substitution, but close enough), so long as the solution is not too concentrated to dissolve all the carbonate needed.

 

[consumptive]

Looking at these published formulas for FX-2 more closely and something is amiss. Jack's website specifies 75grams of potassium carbonate (crystal) and the formula posted by Tom above states 7.5 grams of the same. My Film Developing Cookbook lists the formula twice: once in the section on non-solvent developers, and again in the back as an example of how to mix developers. In one instance its 75 grams potassium carbonate (crystal), in the other 7.5 grams.

Tom - thank you for setting me straight on kodalk=sodium metaborate. hammering this into my head now

 

[gainer]

The FX-2K indeed looks like a good substitute, but 225g of Kodalk seems an awful lot to replace 75g of Pot. carbonate crystals. Does Kodalk have all that many more H2O molecules in it?

Murray

100 grams of sodium metaborate or Kodalk in water is the same as 14.5 grams of sodium hydroxide + 69 grams of borax. The difference in weight is due to water of crystallization in solid metaborate, which will make up part of the water of solution. I used to be concerned about whether Kodalk was 4-mol or 8-mol until I found out that the same metaborate in a closed container could be either 4- or 8-mol depending on temperature. It appears that much is soluble, but whether necessary or not is another question. The pH may in fact not be as high as the carbonate concoction, but concentration and pH both affect activity so it's hard to tell without trying it.

 

[Alan Johnson]

Looking at these published formulas for FX-2 more closely and something is amiss. Jack's website specifies 75grams of potassium carbonate (crystal) and the formula posted by Tom above states 7.5 grams of the same. My Film Developing Cookbook lists the formula twice: once in the section on non-solvent developers, and again in the back as an example of how to mix developers. In one instance its 75 grams potassium carbonate (crystal), in the other 7.5 grams.

Tom - thank you for setting me straight on kodalk=sodium metaborate. hammering this into my head now

The higher concentration (FDC p127,Jackspcs) is the stock solution.The lower concentration (FDC p59) is the working solution.
FDC p60 says to replace potassium carbonate by approximately 1.5 x the amount of Kodalk,which we established is sodium metaborate, to make FX-2K.I have the 1998 (2nd?) edition of the FDC,it definitely says 1.5x the amount.

 

[consumptive]

The higher concentration (FDC p127,Jackspcs) is the stock solution.The lower concentration (FDC p59) is the working solution.
FDC p60 says to replace potassium carbonate by approximately 1.5 x the amount of Kodalk,which we established is sodium metaborate, to make FX-2K.I have the 1998 (2nd?) edition of the FDC,it definitely says 1.5x the amount.

ahh yes, I see. sorry sorry. Obviously I'm new to all this chemistry/mixing (and apparently math). Slowly it is all sinking in... am I looking at stock or working solution? - on guard for that now too. Thank you.

 

[Alan Johnson]

There is a difference in the amount of metaborate given by Jackspcs,225g/L and by the FDC, 1.5x75=112.5g/L.
This kind of error in formulae turns up from time to time. I would trust the Film Developing Cookbook version.