Borax (sodium tetraborate) SUBSTITUTE for sodium metaborate?

[kev curry]

Can Borax (sodium tetraborate) can be substituted for sodium metaborate in PMK?

[Sevo]

No. But a common way to prepare a sodium metaborate solution is by dissolving the appropriate amounts of Borax and sodium hydroxide (approximately a 7:1.5 weight ratio assuming the decahydrate) in water. See http://www.apug.org/forums/forum37/56805-sodium-metaborate-borax-sodium-hydroxide.html for practical formulas.

[kev curry]

Many thanks Sevo.

[IanG]

Only if you add Sodium Hydroxide as well.

10g Sodium Metaborate can be substituted by 7g Borax (sodium Tetraborate) and 1.5g Sodium, that's the recommendation from Kodak in a Databook for DK50

If you want a more accurate sustitution then:


10% Solution Sodium Metaborate

14.5 grams Sodium hydroxide
69 grams Borax (Tetraborate)
Water to make 1 litre.


Some books have an incorrect subtitution, Kodalk is Sodium Metaborate (Octahydrate) which is why the total weight of Borax & Hydroxide is slightly less than the equivalent amount of Kodalk.

Ian

[kev curry]

Thanks Ian thats great. Would that be used at the same dilution as in the PMK Sodium Metaborate solution ie 2 Parts B + 100 Parts of water?

[IanG]

Well PMK Part B uses a 30% stock solution of Sodium Metaborate. So you'd need 43.5 gms Sodium Hydroxide & 207gms Borax per litre of water, you'd have to dissolve the Hydroxide carefully first as it generates heat.

If you used a 10% solution you'd need 1 Part A + 6 Parts B + 100 Parts of water.

Ian

[kev curry]

Thanks Ian thats just great.

[Jarvman]

Thanks also Ian! I was looking for some sodium metaborate tonight for mixing some Rollo Pyro. Do you know if Rollo Pyro also uses a 30% solution as Part B?

I found this on eBay...

http://www.ebay.co.uk/itm/BORAX-Sodium-Tetraborate-Decahydrate-High-Purity-Technical-Grade-/290925810679?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&var=&hash=item43bc8793f7

Part B calls for...

Stock Solution B
Distilled water . . . . . . . . . . . . . . . . . . . . 950 ml
Sodium Metaborate . . . . . . . . . . . . . . . . 150 g

Cheers for the help!

[IanG]

The version in the Darkroom Cookbook 3rd ed uses a 30% Sodium Metaborate solution for Part B

If you use the above version dilute a 30% solution to make a 15% solution.

Ian

[Jarvman]

I think I might've followed the formula in the darkroom Cookbook. In that case use a 30% solution?