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Problems with PMK solution B

olk

Member
Joined
Jul 28, 2020
Messages
107
Location
Germany
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Hi,
I've some problems with solution B of PMK.
Do you have to heat solution B until all Kodalk is dissolved?

What I did:

1.) heat solution B until 300g Kodalk (sodium metaborate tetrahydrate, CAS 10555-76-7) dissolved in water -> 1l
But the solution ‎ precipitate (lot of white crystals) after cooling to room temperatur. Mixing PMK I got the color change but the development times were much longer as expected (30min for Fomapan100@50 for N-development).

2.) as reference I used a older solution B (mixed 1 year ago with different batch of Kodalk) yielding in the correct development times

3.) I mixed solution B without heating. This version of solution B is milky if shaken otherwise half of the 1l bottle contains undissolved Kodalk. With this solution B I don't get a color change.

demineralised water was used

What is going wrong?

Thank you in advance
Oliver
 

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Oliver,

PMK B solution is a saturated solution of Kodalk (sodium metaborate). It is difficult to get it all to dissolve in anything but distilled water. Although, I would imagine that demineralized water would also do...

At any rate, if you're sure that you have the right chemical (Kodalk), then the easy solution (pun intended) is to simply double the volume of the B solution. Everything should dissolve easily in that. Then, just use twice as much B stock solution as normal. You can adjust the total volume of the PMK solution to compensate, but that might not even be necessary.

On the other hand, if the problem is with the chemical itself, then you'll have to get better sodium metaborate. I'm not sure of a way to check the purity of it or to even check if you have the correct reagent.

Maybe one of the chemists here can chime in. Rudi?

Best,

Doremus
 
I got the chemicals from Fototechnik Suvatlar ... never had a problem till now.
 
Not too long ago, I also took from Suvatlar metaborate. It is in rather large, very hard lumps. I have some doubts whether it is not too much impurities or whether it is metaborate at all. Unfortunately, I don't know how to test it...
 

This is exactly what I do. Works great making solution B very easy to mix.
 
lamerko said:
Not too long ago, I also took from Suvatlar metaborate. It is in rather large, very hard lumps. I have some doubts whether it is not too much impurities or whether it is metaborate at all. Unfortunately, I don't know how to test it...
Click to expand...

Yes, the Kodalk I own has large, very hard lumps too.
 
I added 1l of distilled water ro solution B and the chemical did not dissolve.
The pH value is at 8.5 but the pH-meter is a cheap one so I can't coint on it.
 
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The sodium metaborate tetrahydrate, CAS 10555-76-7 I purchased some years ago from Fototechnik Suvatlar worked as expected.
 
lamerko said:
Not too long ago, I also took from Suvatlar metaborate. It is in rather large, very hard lumps. I have some doubts whether it is not too much impurities or whether it is metaborate at all. Unfortunately, I don't know how to test it...
Click to expand...

Did your solution B with the the Kodalk from Suvatlar work?
 
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Instead of mixing up Stock Solution B, why not try dissolving 6 grams of into a liter of distilled water and then adding the 10ml of Stock Solution A to this to make up your working developer. It should make things much easier. Alternately it might be possible to make up a weaker B solution and compensate by just using more solution B when making up the working developer. For example If your solution B was made using 100 grams of water per liter instead of 300 grams you would need to use 3 times as much solution B to make up your working developer. Just make sure to use a little less water to make up the final volume of developer.
 

I've the impression that I don't got Kodalk from Suvatlar ...
 
olk said:
I added 1l of distilled water ro solution B and the chemical did not dissolve.
The pH value is at 8.5 but the pH-meter is a cheap one so I can't coint on it.
Click to expand...

A 30% solution of Sodium Metaborate is supposed to have a pH of around 12 according to borax.com .
A PMK working solution should have a pH of 9.6-9.7.
If it is as low as 8.5, it is not Metaborate and such a pH suggests borax which is a self-buffer around that pH which also explains the solubility issue (less than 100g/L at room temperature)
 
olk said:
Did your solution B with the the Kodalk from Suvatlar work?
Click to expand...

I mixed it with another formula that is only one part. I have only made one attempt to use the resulting PCM18, but the result was disappointing. I'll mix a 0.1% solution with water and I'll measure the pH - it should be around 10.6.
 

Solubility of sodium borate at various temperatures...

16.4 g/100 mL (0 °C)
28.2 g/100 mL (25 °C)
125.2 g/100 mL (100 °C)

You need a warmer darkroom!

Or, as others have suggested, make a more dilute solution and adjust volumes appropriately.
 
I had a call with Mr. Suvatlar - he tested the metaborate and agreed that the metaborate contains unsolvable parts (probably because of some reaction with the moisture). I get a refund + 500g working metaborate.
 
Very good. It's well worth persevering with this.
I use distilled water but start by warming it to about 40°C. It should go into solution but can take a couple of hours.
 
Mark J said:
Very good. It's well worth persevering with this.
I use distilled water but start by warming it to about 40°C. It should go into solution but can take a couple of hours.
Click to expand...

But what would happen when it cools
 
lamerko said:
So... so I don't have a metaborate either
Click to expand...
Probably yes, but Fototechnik Suvatlar gets some new metaborat in April - maybe you ask him for replacing your batch?

I think about to substitute Kodalk with di-sodium tetraborate + sodium hydroxide. But I don't know which tetraborate CAS 1303-96-4 (decahydrat) or 1330-43-4 (anhydrous)?
 
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You need Borax (1303-96-4), but mixing with hydroxide is quite dangerous...
 
lamerko said:
But what would happen when it cools
Click to expand...
If you mean the metaborate which we both own ... Mr. Suvatlar heated the solution to 50°C and added sodium hydroxide. Unfortunately after cooling down the solution went to its original appearance.
 
lamerko said:
You need Borax (1303-96-4), but mixing with hydroxide is quite dangerous...
Click to expand...

Why? I assumed to add first the hydroxide to the water and when the hydroxide was solved the Borax?!
 
olk said:
Why? I assumed to add first the hydroxide to the water and when the hydroxide was solved the Borax?!
Click to expand...

Yup, that'll do it. Not particularly dangerous, nor difficult.
Borax is easy to obtain also for private individuals in Germany. It's used for certain crafts; if you google around, you'll find plenty for sale. Cheap, too.
 
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