DK-25R

[removedacct3]

I would like to mix D-23 replenisher (DK-25R), but I am a little confused about the sodium metaborate ingredient. The anhydrous variant is difficult to source and ridiculously expensive and some online places suggest I can use the tetrahydrate variant. Any insights and where to get it, preferably from a European supplier.

 

[Donald Qualls]

There's a conversion around somewhere to replaced sodium metaborate with borax and sodium hydroxide. I'll try to remember to come back here when I'm at home, I've got it stored on that computer. I can vouch for it working correctly; I ran replenished D-23 for several months back in 2005 or so.

 

[removedacct3]

Yes, I have read that too and I do have caustic soda (lye) at my disposal. But NaOH is highly hydroscopic, so is 1.5g NaOH (and) interchangeable with 1.5g caustic soda?

Nevertheless, thank you very much for the confirmation that I should be able to use Borax/NaOH as a replacement ingredient.

 

[reddesert]

I haven't made this recipe, but the original recipe seems to use Kodak Balanced Alkali (Kodalk). The Darkroom Cookbook says that sodium metaborate can be substituted weight for weight for Kodalk, and they say to use the hydrated form - they say octahydrate, but I suspect they mean tetrahydrate, which would be the usual room temperature form.

Generally, anhydrous variants of chemicals that are hygroscopic are made by baking off the absorbed water, but the difference is also generally irrelevant for photographic chemicals. You're going to dissolve it in water anyway. You just have to make sure to understand whether the weight in the recipe is for the anhydrous or the hydrated form, and convert the weight if needed.

 

[john_s]

The naming of the hydration of sodium metaborate has been confusing. The following was copied from Ryuji Suzuki's web site before he discontinued it. It is probably still available in the wayback machine (web archives).

<Start of Quotation>

Hydration of sodium metaborate, NaBO2, and that of Kodalk

Kodalk or "Kodak balanced alkali" is Eastman Kodak Company's trade name for sodium metaborate. The largest supplier and research institution for this compound is U.S. Borax Research Corp. in Anaheim, California. In Ullmann's Encyclopedia of Industrial Chemistry, Robert A. Smith of U.S. Borax explains industrial production processes for this compound among other boron compounds in detail.

In old literature, sodium metaborate tetrahydrate (CAS 10555-76-7) is denoted Na2B2O4 - 8H2O. This lead to old nomenclature describing hydration of sodium metaborate to be octahydrate. However, as more modern techniques became available, the actual structure of sodium metaborate is known to be better described by NaB(OH)4 - 2H2O, and this substance became to be commonly denoted by NaBO2 - 4H2O, hence tetrahydrate. According to detailed catalogues of several laboratories chemical suppliers, there is no NaBO2 - 8H2O commonly traded today. Robert Smith of U.S. Borax explains that "sodium metaborate tetrahydrate is the stable solid phase in contact with its saturated solution between 11.5 and 53.6°C." Therefore, octahydrate in old nomenclature and tetrahydrate in modern nomenclature indicate the identical chemical in the same hydration form. It is just that the nominal formula weight for tetrahydrate is half that of octahydrate. One mole of tetrahydrate would provide one mole of B(OH)4- in aqueous solution, while octahydrate would provide two moles.

The formula weight for this sodium metaborate tetrahydrate is 137.8. Common procedures for making sodium metaborate from borax and sodium hydroxide are often based on incorrect assumption that Kodalk is actually NaBO2 - 8H2O, and they have to be corrected. Fortunatelly, the proportion of mixture is correct, and the error is in final dilution, so solutions made from incorrect instruction can still be used, but by increased amount.

In order to make 1.0g sodium metaborate tetrahydrate, mix 0.692g borax and 0.145g sodium hydroxide. When dissolved in water, these two make solutions of identical composition.

<end>

 

[Donald Qualls]

Here's the formula I've used in the past for DK-25R:

Balanced Alkali Replenisher (aka DK-25R)

Add 22 ml per 135-36, 120, or 8x10 equivalent developed, discarding developer if needed to maintain volume. Formula contains sodium hydroxide and borax equivalent to 20.0 grams sodium metaborate, aka Kodak Balanced Alkali (Kodalk). My source gives no indication how long replenishment may be carried on with D-23, so one will need to watch for changes in negatives.

750 ml Water
10.0 g Metol
100.0 g Sodium Sulfite
1.9 g Sodium Hydroxide
9.8 g Borax

Water to make 1.0 L

I have always bought sodium hydroxide as drain opener lye; yes, this is hygroscopic, and will also absorb carbon dioxide from the air, but if it absorbs more than a few percent of water, the beads in the can will clump. My rule has been that if I can't scoop it out with a teaspoon without risk of flinging crystals around the room, it's gotten too damp and I replace it. In the past, using it mainly to mix Parodinal (so a few grams a month), I've gotten through about 2/3 of a can before this occurs (tightly closing the can after each use, of course). You could also make it up as a high concentration solution, but you can't store this in glass -- it'll eat the glass.

 

[removedacct3]

Here's the formula I've used in the past for DK-25R:
... but if it absorbs more than a few percent of water, the beads in the can will clump. ...

I did not know that. That is useful information. Thank you!

 

[Christiaan Phleger]

Yes thank you Donald that is a useful formula.