Kodalk substitute

Relayer · Jul 19, 2012

Hello

In my country Kodalk (sodium metaborate) isn't available for purchase. I know what kodalk can be replaced with borax+NaOH and sometime I used this. But now I want find other solution for buffer with same pH, because I don't like working with NaOH.
I found that carbonate-bicarbonate isn't good for kodalk replacement because optimal pH range for this system is 9.5..10.5.
Other possible substitution is DEA with pH in range 10.5..11.5. Maybe mixture of TEA+DEA will be good buffer in range 10..11.
In Anchell "Darkroom Cookbook" I found next recomendation for substitute kodalk:

Yet another substitution is to use 4 parts sodium carbonate, monohydrate, and 1 part borax to equal the same weight of Balanced Alkali (e.g., 10.0 grams of Balanced Alkali equals 8.0 grams of carbonate and 2.0 grams of borax).

I haven't found any details in google about carbonate-borax buffer, just only that such type of buffer used for pH in range 10-11. Someone try this?

Keith Tapscott. · Jul 19, 2012

From a Kodak formulary, 2 grams of "KODALK" (sodium metaborate) can be substituted with 0.3 gram of sodium hydroxide (caustic soda) and 1.4 grams of Borax (decahydrate).

Gerald C Koch · Jul 19, 2012

In which formula would you want to replace Kodalk?

Relayer · Jul 19, 2012

not in 2bath. DK-76, DK-50 and other

Gerald C Koch · Jul 19, 2012

Substituting one chemical for another in a developer is an "iffy" situation. I would say to try Anchell's suggestion but to test it first. If the negatives are too contrasty then reduce the ratio of carbonate to borate.

Relayer · Jul 20, 2012

ohh ... yes, I can mix carbonate+borax in different proportion and measure pH of solution but open question - what is the target pH of DK-50?

Ian Grant · Jul 20, 2012

The correct substitution is as Keith says 10gm Sodium Metaborate (Kodalk) is equivalent to 7gm Borax and 1.5g Sodium Hydroxide, and this substitution has been in use for well over 50 years.

Kodak have published this substitution themselves in Professional Handbooks and it's reliable. Kodalk hasn't been available in the UK for many years.

Ian

Mr Bill · Jul 20, 2012

Relayer said:
ohh ... yes, I can mix carbonate+borax in different proportion and measure pH of solution but open question - what is the target pH of DK-50?

There is an MSDS here, which says pH = 9.5 for a working solution: http://www.chemcas.com/msds112/cas/4204/7732-18-5_7757-83-7_7775-19-1_123-31-9_55-55-1.asp

I don't know how reliable this number is, though.

PhotoJim · Jul 20, 2012

You could possibly get sodium metaborate from Photographer's Formulary in the US. They ship it to Canada; I imagine they can ship it anywhere.

It lasts a long time so if you buy a good amount you will have a supply that will last you for many years, possibly justifying the shipping expense.

Gerald C Koch · Jul 20, 2012

Having practiced photography for over 60 years I have never seen a pH value given for DK-50. This is why I suggested running a few test negatives and adjusting the ratio of carbonate to borate on the basis of the tests. If the negatives are too contrasty then reduce the ratio (less carbonate). If they lack contrast then increase the ratio.

Ian Grant · Jul 20, 2012

Why not make it up properly like Kodak themselves suggested with 7.5gms Borax and 1.5gms Sodium Hydroxide instead of 10gms Kodalk/Sodium Metaborate ?

Ian

BradS · Jul 20, 2012

I had this same question some years ago....I'm not a chemistry person so, it took me several hours to figure this out but, here's the way I see it....

2NaOH + Na2B4o7(10H2O) + 5H2O <-->> 4NaBO2(4H2O)

2 mols lye + 1 mol Borax (in water) is equivalent to 4 mols Kodalk in water

80g lye + 381.37g Borax (in water) is equivalent to 551.42g Kodalk in water.

divide each of these by 5.5142 and we have:

14.5g Sodium Hydroxide (Lye) + 69.2g Borax dissolved in water is equivalet to 100g of Kodalk (dissolved in water.

Of course, you may wish to divide by 55.142 to get...

1.45G Lye + 6.9g Borax (dissolved in water) is the equivalent of 10g of Kodalk dissolved in water.

The difficulty with this whole approach is always measuring out the Lye accurately. It suck water out of the air so fast you can actually watch it gain weight on a scale.

(EDIT: or, do as Ian suggests above!)

Ian Grant · Jul 20, 2012

BradS said:
(EDIT: or, do as Ian suggests above!)

More importantly as KODAK SUGGEST

Ian

Rudeofus · Jul 20, 2012

As mentioned in that other thread, there is a (there was a url link here which no longer exists) described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax. I'd add half the moles of Na2CO3 as there are moles of NaOH in the original recipe and go from there.

Gerald C Koch · Jul 20, 2012

Relayer said:
But now I want find other solution for buffer with same pH, because I don't like working with NaOH.

This statement by the OP seems to be forgotten. He already knows how to make sodium metaborate from borax and sodium hydroxide but would like an alternate.

BTW, you cannot make sodium metaborate from sodium carbonate and sodium borate from just mixing them in solution. The only way to make it is to fuse the two chemicals at red heat. The average person does not have the equipment to do this.

Relayer · Jul 20, 2012

Rudeofus said:
As mentioned in that other thread, there is a (there was a url link here which no longer exists) described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax. I'd add half the moles of Na2CO3 as there are moles of NaOH in the original recipe and go from there.

hmm...

Na2B4O7.10*H2O + 2*NaOH + 5*H2O --> 4*NaBO2 + 16*H2O

so

Na2B4O7.10H2O + Na2CO3 + 6*H2O --> 4*NaBO2 + 16*H2O + CO2

381.37g of Borax + 106g of Sodium Carbonate = 551.2g Kodalk (sodium metaborate + water NaBO2·4H2O )
and for 10g of Kodalk we need mix 6.92g of Borax with 1.92 of Sodium carbonate

Rudeofus · Jul 20, 2012

Gerald C Koch said:
BTW, you cannot make sodium metaborate from sodium carbonate and sodium borate from just mixing them in solution. The only way to make it is to fuse the two chemicals at red heat. The average person does not have the equipment to do this.

And doesn't need to. Relayer doesn't want to supply the world market with 99.9% pure Kodalk, he wants a buffer at pH 8.2 for a photographic developer. At this pH any extra CO32-, HCO3- or CO2 won't make much of a difference. If it did, the dev could not be used after much exposure to air anyway.

Mike Wilde gave his recipe specifically because NaOH picks up CO2 after some time. I really don't think there is much of a difference between making it with carbonate vs. lye but I'm open to learning.

@Relayer: If you are concerned about the surplus of CO2, you could leave it standing in air for a while. I'm not aware of any harm air could do to metaborate.

Relayer · Jul 20, 2012

Rudeofus said:
And doesn't need to. Relayer doesn't want to supply the world market with 99.9% pure Kodalk, he wants a buffer at pH 8.2 for a photographic developer.

yes, you right. I'm find some easy-to-mix buffer solution that give me different range of pH and and also allow substitute kodalk

just make some experiment: in 1l of water at 32C dissolve 1.92g of Sodium carbonate. then add 6.92g of borax - its dissolved very quickly! solution is muddy, but clear after 2-3min. check pH - 9.2 at 24C. now put this solution in open bottle and will be recheck pH later

Gerald C Koch · Jul 20, 2012

Rudeofus said:
As mentioned in that other thread, there is a (there was a url link here which no longer exists) described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax.

Certainly one can make a buffer from carbonate and borate but the last sentence is not true. Sodium carbonate is not sufficiently alkaline to react with borax in water like sodium hydroxide can.

Relayer · Jul 20, 2012

Gerald C Koch said:
Sodium carbonate is not sufficiently alkaline to react with borax in water like sodium hydroxide can.

not agree - you forget about hydrolyze.

Gerald C Koch · Jul 20, 2012

Relayer said:
not agree - you forget about hydrolyze.

You can certainly try mixing sodium carbonate and borax together in water but speaking as a chemist it's not going to make sodium metaborate.

Photo Engineer · Jul 20, 2012

During the war, Agfa used a Kodalk substitute. I would have to go back over a lot of notes to find this, but if you need it, I might be able to find it. A simple solution exists. I know that, but it is hidden in reams of notes. sorry.

PE

Rudeofus · Jul 21, 2012

Gerald C Koch said:
You can certainly try mixing sodium carbonate and borax together in water but speaking as a chemist it's not going to make sodium metaborate.

There is little chance that sodium metaborate is actually present in substantial amounts at pH of 8.2. Let's look at an excerpt from this table of buffers:

[TABLE="class: cms_table_grid, width: 500"]
Buffer pH range
Sodium tetraborate/ Hydrochloric acid 8.1 - 9.2
Sodium tetraborate/ Sodium hydroxide 9.3 - 10.7
Sodium carbonate/ Sodium hydrogen carbonate 9.2 - 10.8
[/TABLE]

This table suggests that below pH of 9 there is an equilibrium between borax and boric acid, no matter which borate compound you started with, and that the carbonate won't interfere all that much. I seriously doubt that there would be a noticeable difference between NaOH+Borax and Na2CO3+Borax once the remaining compounds are added to make pH of 8.2.

So, yes, you may be right in theory, Na2CO3+Borax don't make metaborate in aqueous solution, but they do make something which behaves very very similar to metaborate once pH is set below 9. Let's face it: all these recipes list metaborate because it is much easier to dissolve initially than borax or boric acid, not because of its pH buffer range.

RalphLambrecht · Jul 21, 2012

the darkroom cookbook3rd ed shows another substitution on page 329as sodium carbonate multiplied by 0.59. i never tried it though.

sharperstill · Jul 21, 2012

BradS said:
I had this same question some years ago....I'm not a chemistry person so, it took me several hours to figure this out but, here's the way I see it....

2NaOH + Na2B4o7(10H2O) + 5H2O <-->> 4NaBO2(4H2O)

2 mols lye + 1 mol Borax (in water) is equivalent to 4 mols Kodalk in water

80g lye + 381.37g Borax (in water) is equivalent to 551.42g Kodalk in water.

divide each of these by 5.5142 and we have:

14.5g Sodium Hydroxide (Lye) + 69.2g Borax dissolved in water is equivalet to 100g of Kodalk (dissolved in water.

Of course, you may wish to divide by 55.142 to get...

1.45G Lye + 6.9g Borax (dissolved in water) is the equivalent of 10g of Kodalk dissolved in water.

The difficulty with this whole approach is always measuring out the Lye accurately. It suck water out of the air so fast you can actually watch it gain weight on a scale.

(EDIT: or, do as Ian suggests above!)

You're NOT a chemistry person? Fooled me.

Jon

Kodalk substitute

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